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Drug and Alcohol Review (March 2015), 34, 141–146 DOI: 10.1111/dar.12207
Prevalence of medical marijuana use in California, 2012 SUZANNE RYAN-IBARRA*, MARTA INDUNI* & DANIELLE EWING Survey Research Group, Public Health Institute, Sacramento, California, USA
Abstract Introduction and Aims. The US Drug Enforcement Agency classifies marijuana as an illegal substance, yet in 22 states marijuana is legal for medicinal use. In 1996, California legalised the use of marijuana for medicinal purposes, but population-based data describing medical marijuana users in the state has not been available. Our aim was to examine the demographic differences between users and non-users of medical marijuana in California utilising population-based data. Design and Methods. We used data from the California Behavioral Risk Factor Surveillance System 2012, an annual, random-digit-dial state-wide telephone survey that collects health data from a representative adult sample (n = 7525). Age-adjusted prevalence rates were estimated. Results. Five percent of adults in California reported ever using medical marijuana, and most users believed that medical marijuana helped alleviate symptoms or treat a serious medical condition. Prevalence was similar when compared by gender, education and region. Prevalence of ever using medical marijuana was highest among white adults and younger adults ages 18–24 years, although use was reported by every racial/ethnic and age group examined in our study and ranged from 2% to 9%. Conclusions. Our study’s results lend support to the idea that medical marijuana is used equally by many groups of people and is not exclusively used by any one specific group.As more states approve marijuana use for medical purposes, it is important to track medical marijuana use as a health-related behaviour and risk factor. [Ryan-Ibarra S, Induni M, Ewing D. Prevalence of medical marijuana use in California, 2012. Drug Alcohol Rev 2015;34:141–6] Key words: epidemiology, cannabis, harm reduction.
Introduction The US Drug Enforcement Agency classifies marijuana as an illegal Schedule 1 substance with no accepted medical use. However, a statement from the American College of Physicians and an Institute of Medicine report recommend that cannabis continue to be studied and used to treat patients who do not respond to conventional treatments for certain medical conditions [1]. In the USA, 22 states and the District of Columbia have legalised herbal medical marijuana from dried parts of the plant, Cannabis sativa. California was the first state in the nation to legalise medical marijuana. The Compassionate Use Act of 1996 (Proposition 215) added a section to California’s Health and Safety Code approving the use of herbal medical marijuana when recommended by a physician for a serious medical condition or ‘for any other illness for which marijuana provides relief’.
Marijuana contains over 400 compounds, and 66 compounds are defined as cannabinoids due to their carbon structure. Tetrahydrocannabinol and cannabidiol are the most commonly studied cannabinoids and have pharmacological effects, such as appetite stimulation, muscle relaxation and anti-inflammatory effects [2,3]. Evidence from randomised controlled trials suggests that cannabinoids can improve quality of life by improving sleep, increasing appetite and reducing chronic pain for people with chronic conditions [4,5], especially when these conditions do not respond to conventional treatments [1]. Some evidence indicates an enhanced quality of life, including improved well-being, for users of medical marijuana with chronic diseases [6,7]. In spite of the evidence that marijuana can be a useful medicine, it also carries physical and mental health risks. Regular or habitual marijuana smoking can have deleterious effects on lung health and is positively
Suzanne Ryan-Ibarra MPH, MS, Research Scientist, Marta Induni PhD, Research Program Director, Danielle Ewing MPH, Research Associate. Correspondence to Ms Suzanne Ryan-Ibarra, Survey Research Group, Public Health Institute, 1825 Bell Street, Suite 102, Sacramento, CA 95825, USA. Tel: 916 779 0115; Fax: 916 779 0265; E-mail: [email protected] *SRI and MI contributed equally towards this work. Received 10 February 2014; accepted for publication 14 August 2014. © 2014 Australasian Professional Society on Alcohol and other Drugs
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associated with chronic bronchitis and airway inflammation [8]. Previous studies have found that marijuana use is positively associated with depression, panic attacks, psychosis, schizophrenia and suicidal ideation [9–15]. One recent study using data from the US National Vital Statistics System’s Mortality Detail Files observed that states where medical marijuana was legal had lower rates of suicide among young men [16]. It is unclear what mechanism explains the observed lower rates of suicide, although the authors speculate that prior studies that found positive associations between suicidal ideation and marijuana use could reflect reverse causation due to self-medication [16]. Prior studies have described characteristics of medical marijuana users in California who have applied for medical marijuana licenses, but none have used population-based surveillance data to describe users [17]. This report summarises results from populationbased health surveillance of medical marijuana use among adults in California. To our knowledge, population-based surveillance data on medical marijuana use among adults in California has not been available before. Methods The California Behavioral Risk Factor Surveillance System (CA BRFSS) is part of the BRFSS, which is an ongoing, cross-sectional telephone survey of the noninstitutionalized US civilian population age 18 years and older. In 2012, CA BRFSS data were collected from a random sample of California adults with landline and cellular telephones, and interviews were conducted in English and Spanish (n = 7525). Medical marijuana use was assessed by asking, ‘Have you ever used medical marijuana for a serious medical condition?’ Participants who answered ‘yes’ were defined as having ever used medical marijuana. Those who answered ‘don’t know’ or ‘refused’ were excluded from analyses. If a participant needed more information about what was considered a serious medical condition, interviewers provided a list of conditions as defined by California Senate Bill 420 [18]. This study was approved by the California Department of Public Health’s Institutional Review Board and conforms to the provisions of the Declaration of Helsinki (as revised in Tokyo 2004). Overall prevalence of medical marijuana use was estimated. Prevalence of satisfaction with medical marijuana for treatment and reasons for use was estimated. Prevalence of medical marijuana use according to demographic and social factors was estimated using the following factors: age group, sex, race-ethnicity (nonHispanic white; non-Hispanic black or African American; Hispanic or Latino; non-Hispanic Asian, Pacific © 2014 Australasian Professional Society on Alcohol and other Drugs
Islander, American Indian, Alaska Native, or other), education and region. Age-adjusted prevalence estimates, standardised to the 2010 California standard population, are presented. Prevalence estimates were weighted and represent the California adult population according to 2010 California Department of Finance figures. Results Five percent of adults in California reported ever using medical marijuana (Table 1). Of these, most reported that medical marijuana helped treat a serious medical condition (92%), and the most commonly reported conditions were chronic pain (31%), arthritis (11%), migraine (8%) and cancer (7%). Other conditions reported include: AIDS, glaucoma, muscle spasms, nausea, stress and depression. Prevalence of medical marijuana use was higher among white adults (7%), compared with other race or ethnicity groups. Prevalence of medical marijuana use was higher among younger adults ages 18–24 years (9%), compared with middle-aged and older adults, although middle-aged and older adults still reported some medical marijuana use. Prevalence of medical marijuana use was similar for men and women (6% vs. 5%). Medical marijuana use was similar by region, with similar prevalence rates reported for those living in the Greater Northern California region (6%), compared with the San Francisco Bay Area (4%) or Southern California (4%). Adults with a high school degree or GED were more likely to have ever used medical marijuana use than adults who had completed at least some college or more (7% vs. 5%). Discussion We found that nearly one in 20 adults in California has used medical marijuana at least once, and most users believed that medical marijuana helped alleviate symptoms or treat a serious medical condition. Our results are from a large dataset that is representative of the California adult population. To our knowledge, our study is the first to publish population-based prevalence estimates of medical marijuana use in California. Our sampling strategy allows population comparisons of medical marijuana use by age, race/ethnicity and other demographic variables that previous studies have examined. Our study found that adults in California who had ever used medical marijuana were overwhelmingly satisfied with its ability to treat and manage their serious medical conditions. The most commonly reported reasons for use were chronic pain, arthritis, migraine and cancer. Similarly, other studies conducted in
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Table 1. Prevalence of medical marijuana use among adults in California (California Behavioral Risk Factor Surveillance System, 2012) Total, Ever used medical Ever used medical Age-adjusted n marijuana, n marijuana, weighted n weighted percenta Total Demographic characteristics Age 18–24 years 25–34 years 35–44 years 45–54 years 55–64 years 65+ years Sex Male Female Race White Hispanic or Latinob African American Asian, Pacific Islander or otherc Educational level Less than high school diploma or GED test High school diploma or GED test At least some college Region San Francisco Bay Area, Californiad Greater Northern Californiae Southern California Marijuana-related characteristics Did marijuana help your serious medical condition(s)? Yes Medical marijuana used for: Chronic pain Arthritis Migraine Cancer
(95% CI)
7525
350
1 078 795
5.15
(4.56–5.83)
415 824 1101 1304 1505 2376
41 50 44 76 85 54
271 674 212 171 171 897 205 569 145 653 71 831
9.28 5.52 4.39 5.20 4.64 2.19
(6.32–12.23) (3.88–7.17) (2.95–5.83) (3.82–6.57) (3.50–5.77) (1.52–2.86)
3135 4390
179 171
597 524 481 272
5.73 4.61
(4.69–6.76) (3.68–5.53)
4876 1733 342 574
251 52 21 26
623 942 235 973 61 171 157 709
7.41 3.33 5.12 4.18
(6.13–8.69) (2.34–4.31) (2.35–7.89) (2.38–5.97)
845
43
142 196
5.38
(3.31–7.46)
1373 5302
83 224
311 055 625 543
6.58 4.57
(4.96–8.20) (3.72–5.42)
1541 1508 4141
72 78 163
186 883 251 686 532 152
4.27 6.38 4.48
(2.92–5.61) (4.66–8.10) (3.62–5.35)
350
320
995 306
92.03
(88.76–95.30)
350 350 350 350
115 38 25 26
300 872 96 917 99 408 64 194
31.12 10.70 8.43 6.75
(25.28–36.96) (6.84–14.55) (4.74–12.11) (3.31–10.19)
a Weighted estimates were age-adjusted using California Department of Finance 2010 population estimates. bHispanic or Latino participants might be of any race. cAsian, Pacific Islander and Other includes Alaska Native and American Indian. dSan Francisco Bay Area includes Alameda, Contra Costa, Marin, Napa, San Francisco, San Mateo, Santa Clara, Solano and Sonoma Counties. e Greater Northern California excludes San Francisco Bay Area. CI, confidence interval; GED, General Educational Development test.
California and Canada have found that medical marijuana is frequently used to relieve pain (including chronic pain), headaches and arthritis [19–21]. In contrast to our findings, other studies have reported that cancer was one of the least common reasons for use among Canadians who use cannabis for therapeutic purposes [20]. When comparing prevalence of medical marijuana use by demographic factors, some findings were similar to prior studies, whereas others were different. Similar to previous studies, we found that those who had completed high school were more likely to report ever using medical marijuana, compared with those who had completed less or more education [17,19,20]. Our study
found similar rates of medical marijuana use among men and women (5.73% and 4.61%, respectively).This contrasts with previous studies who recruited participants at clinics and medical cannabis dispensaries, which found much higher rates of medical marijuana use among men as compared with women [17,19,20]. We found that medical marijuana has been used by adults of all ages in California, but younger adults aged 18- to 24-years-old have the highest prevalence of ever using medical marijuana. Because older age generally increases one’s risk for experiencing disease, it is surprising that those who are older do not have higher rates of ever using medical marijuana. It may be that medical marijuana is still not an accepted way to cope with © 2014 Australasian Professional Society on Alcohol and other Drugs
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diseases, such as cancer among older adults. Analyses using the National Survey on Drug Use and Health data have found that those born after 1950 have much higher rates of illicit drug use, including marijuana, as young adults [22]. Those born after 1950 were age 62 years and older in our sample, which may partly explain the very low rates of ever using medical marijuana in our study’s for those age 65 years and older in our study. As those who were born after 1950 become older, rates of ever using medical marijuana may rise due to increased acceptance of using illicit drugs, including marijuana, among this group. We found that non-Hispanic whites were more likely to report ever using medical marijuana, as compared with other racial/ethnic groups, including African Americans.This is similar to other studies conducted in California and Canada [17,20] but contrasts with others, which have found that African Americans were overrepresented [19]. Although we found that whites were more likely to report ever using medical marijuana compared with other racial/ethnic groups, we urge that this finding be interpreted cautiously. The absolute difference in prevalence between the racial/ethnic groups is less than three percentage points, which may not have much importance in practical terms. Medical marijuana use to treat serious medical conditions and recreational marijuana use are motivated by different factors. However, some medical marijuana use among California adults may be measured in surveys of drug use because the US federal government classifies it as an illegal Schedule 1 substance. Survey participants who are medical marijuana users may answer ‘yes’ to questions about using marijuana in these surveys. National Survey on Drug Use and Health 2010–2011 estimates that 10% of adults ages 26 and older in California used marijuana in the past year, which is double our overall estimate of medical marijuana use. Among young adults age 18–25 years old in California, 33% reported using marijuana at least once in the previous year [23]. This is more than three times the rate of ever using medical marijuana our study observed among young adults age 18 to 24 years old. Why are these results important? Our study contradicts commonly held beliefs that medical marijuana is being overused by healthy individuals by collecting data from a representative, population-based sample of users and asking them why they use medical marijuana. The CA BRFSS is a random-digit-dial telephone survey of a populationbased, representative sample of non-institutionalised adults ages 18 and older. In 2012, this survey became more inclusive and began to include a sample of cellphone only households.This is important because more © 2014 Australasian Professional Society on Alcohol and other Drugs
than one-third of adults in CA live in a household that relies on cellular phones for most or all of telephone communication [24]. The results from this survey are well-recognised as accurately measuring health-related behaviours, and data from this survey have been used for the past three decades to provide information on prevalence of health-related behaviours among population groups in states and the nation [25]. Self-reported data from the BRFSS describing health behaviours benchmark to other data sources, including national surveys that collect data via in-person interview [25]. Weighting techniques adjust for non-response so that prevalence estimates accurately reflect the population of the state [25,26]. Unlike other studies that have described characteristics of users using purposive samples of users at clinics or cannabis-focused organisations [17,20,21], our study’s population-based, representative sample of California adults allows us to generate prevalence estimates of medical marijuana use according to demographics and describe the perceived benefits and reasons for use. The most common reasons for use include medical conditions for which mainstream treatments may not exist, such as for migraines, or may not be effective, including for chronic pain and cancer. A limitation of our study is that we did not ask which symptoms medical cannabis helped users manage; for example, other studies of characteristics of medical cannabis users have asked which symptoms medical cannabis helped treat, including increasing appetite and improving sleep disturbances [19–21]. How can these results be used, and by whom? Our study’s results lend support to the idea that medical marijuana is used equally by many groups of people and is not exclusively used by any one specific group. Rather, medical marijuana is used at similar rates by men and women, young and old, high and low educated and in diverse regions throughout California. First, it is clear that Proposition 215 is helping people who are sick and use medical marijuana to treat serious medical conditions, including cancer, migraines and chronic pain, to manage their symptoms. Medical marijuana is not solely being used by young men who are accessing medical marijuana under the pretence that they have a serious medical condition and that they ‘need’ medical marijuana to treat it. A perception persists that medical marijuana users may not ‘need’ to use it to treat a serious medical condition [27]. Our study found evidence via anonymous, self-reported data that users commonly employed medical marijuana to treat serious medical conditions. Second, some people who access medical marijuana in California may not truly be using it to treat a serious medical condition. Our data
Medical marijuana in California
did not allow us to verify the self-reported diagnoses reported by medical marijuana users, but the similar prevalence rates of use among men and women, as well as by most age groups, suggest that medical marijuana is used by many groups of people. Nearly all of the people in our study who used medical marijuana reported that it helped them treat a serious medical condition. Limitations This report has limitations. First, the CA BRFSS is a telephone survey that includes only the noninstitutionalised population, so results might not apply to groups living in institutions, such as nursing homes and long-term care facilities [26]. Second, the CA BRFSS is conducted only in English and Spanish and excludes those who do not speak those languages well enough to participate in a survey [26]. Third, participating in the CA BRFSS is voluntary, and response rates for telephone surveys, including the BRFSS, have been steadily declining over the past few decades [28,29]. However, the CA BRFSS attempts to mitigate this by using weighting to adjust for non-response and adding a random-digit-dial cell phone sample to the random-digit-dial landline sample [25,26]. Fourth, CA BRFSS data are self-reported [26] and subject to social desirability bias. Social desirability bias occurs when people respond to questions in a socially acceptable manner and tends to occur for questions that are socially sensitive [30]. Even though medical marijuana is legal in California, questions about ever using medical marijuana may qualify as socially sensitive due to the stigma around using it [27] and because it is classified as an illegal Schedule I substance by the US federal government. If this bias affected responses to our study’s question, responses to ever using medical marijuana would be underreported and therefore, our reported prevalence estimates would be biased towards the null. Conclusions Our results highlight that medical marijuana is commonly used to treat serious medical conditions, including cancer, migraines and chronic pain, among California adults. Our study points out that Proposition 215 allows legal access to medical marijuana among California adults, and the group that reports ever using medical marijuana is diverse and composed of many age, gender, education and racial/ethnic groups. Therefore, it is surprising that stigma continues to be experienced by those that utilise medical marijuana. Even though those who are younger and white are more likely to report ever using medical marijuana than their older
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or non-white counterparts, our study shows that medical marijuana is used by a diverse population and is not limited to any specific age, gender, racial/ethnic or education group. Proposition 215 allows access to medical marijuana for many people, some of whom may not truly need medical marijuana, but many of whom probably do. The law benefits the sick, but also may allow for expanded legal use among young people, as observed in the higher prevalence of ever using medical marijuana among young adults in our study. Additional research should be conducted to determine predictors or correlates of medical marijuana use using population-based data. Furthermore, future research should evaluate whether rates of use according to condition vary according to demographic characteristics. Such research could be used to target medical marijuana use by demographics and serious medical condition, particularly when medical marijuana is known to be an effective treatment for certain serious medical conditions. Acknowledgements We would like to recognise and thank the participants in the 2012 CA BRFSS. This study would not have been possible without their valuable time and willingness to share personal information. References [1] American College of Physicians. Supporting research into the therapeutic role of marijuana. American College of Physicians Position Paper [Internet]. 2008. Available at: http:// www.acponline.org/advocacy/where_we_stand/other _issues/medmarijuana.pdf (accessed October 2012). [2] Grant I, Cahn BR. Cannabis and endocannabinoid modulators: therapeutic promises and challenges. Clin Neurosci Res 2005;5:185–99. [3] Pertwee RG. The diverse CB1 and CB2 receptor pharmacology of three plant cannabinoids: delta9tetrahydrocannabinol, cannabidiol and delta9tetrahydrocannabivarin. Br J Pharmacol 2008;153: 199–215. [4] Lynch ME, Campbell F. Cannabinoids for treatment of chronic non-cancer pain; a systematic review of randomized trials. Br J Clin Pharmacol 2011;72:735–44. [5] Zajicek JP, Hobart JC, Slade A, Barnes D, Mattison PG, on behalf of the MUSEC Research Group. Multiple sclerosis and extract of cannabis: results of the MUSEC trial. J Neurol Neurosurg Psychiatry 2012;83:1125–32. [6] Aggarwal SK, Carter GT, Sullivan MD, et al. Characteristics of patients with chronic pain accessing treatment with medical cannabis in Washington State. J Opioid Manag 2009;5:257–86. [7] Fiz J, Durán M, Capellà D, Carbonell J, Farré M. Cannabis use in patients with fibromyalgia: effect on symptoms relief and health-related quality of life. PLoS ONE 2011; 6:e18440. García AV, editor. [8] Joshi M, Joshi A, Bartter T. Marijuana and lung diseases. Curr Opin Pulm Med 2014;20:173–9. © 2014 Australasian Professional Society on Alcohol and other Drugs
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[9] Bovasso GB. Cannabis abuse as a risk factor for depressive symptoms. Am J Psychiatry 2001;158:2033–7. [10] Fergusson DM, Horwood LJ, Swain-Campbell N. Cannabis use and psychosocial adjustment in adolescence and young adulthood. Addiction 2002;97:1123–35. [11] Zammit S, Allebeck P, Andreasson S, Lundberg I, Lewis G. Self reported cannabis use as a risk factor for schizophrenia in Swedish conscripts of 1969: historical cohort study. BMJ 2002;325:1199. [12] Henquet C, Krabbendam L, Spauwen J, et al. Prospective cohort study of cannabis use, predisposition for psychosis, and psychotic symptoms in young people. BMJ 2005; 330:11. [13] Zvolensky MJ, Bernstein A, Sachs-Ericsson N, Schmidt NB, Buckner JD, Bonn-Miller MO. Lifetime associations between cannabis, use, abuse, and dependence and panic attacks in a representative sample. J Psychiatr Res 2006;40:477–86. [14] Rey JM, Sawyer MG, Raphael B, Patton GC, Lynskey M. Mental health of teenagers who use cannabis. Results of an Australian survey. Br J Psychiatry 2002;180:216–21. [15] Moore THM, Zammit S, Lingford-Hughes A, et al. Cannabis use and risk of psychotic or affective mental health outcomes: a systematic review. Lancet 2007;370:319–28. [16] Anderson DM, Rees DI, Sabia JJ. Medical marijuana laws and suicides by gender and age. Am J Public Health 2014;e1–8. doi: 10.2105/AJPH.2013.301612. [17] O’Connell TJ, Bou-Matar CB. Long term marijuana users seeking medical cannabis in California (2001–2007): demographics, social characteristics, patterns of cannabis and other drug use of 4117 applicants. Harm Reduct J 2007;4:16. [18] California Department of Public Health. Compassionate Use Act—Medical Marijuana Program [Internet]. Available at: http://www.cdph.ca.gov/programs/MMP/Pages/Compas sionateUseact.aspx (accessed October 2012). [19] Reinarman C, Nunberg H, Lanthier F, Heddleston T. Who are medical marijuana patients? Population characteristics from nine California assessment clinics. J Psychoactive Drugs 2011;43:128–35. [20] Walsh Z, Callaway R, Belle-Isle L, et al. Cannabis for therapeutic purposes: patient characteristics, access, and reasons for use. Int J Drug Policy 2013;24:511–6.
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[21] Lucas P. It can’t hurt to ask; a patient-centered quality of service assessment of Health Canada’s medical cannabis policy and program. Harm Reduct J 2012;9:2. [22] Substance Abuse and Mental Health Services Administration. Results from the 2012 National Survey on Drug Use and Health: Summary of National Findings. Rockville, MD: Substance Abuse and Mental Health Services Administration. Report No.: 13-4795, 2013. [23] Substance Abuse and Mental Health Services Administration. 2010–2011 National Survey on Drug Use and Health: Model-Based Prevalence Estimates (50 States and the District of Columbia). Rockville, MD: Substance Abuse and Mental Health Services Administration, March 2012. [24] Blumberg SJ, Ganesh N, Luke JV, Gilbert Gonzales MHA. Wireless Substitution: State-level Estimates from the National Health Interview Survey, 2012. Methods [Internet]. 2011. 2013. Available at: http://198.246.124.29/nchs/ data/nhsr/nhsr070.pdf (accessed May 2014). [25] Pierannunzi C, Hu SS, Balluz L. A systematic review of publications assessing reliability and validity of the Behavioral Risk Factor Surveillance System (BRFSS), 2004–2011. BMC Med Res Methodol 2013;13:49. [26] Ryan-Ibarra S, Induni M, Zuniga M, Ewing D. California Behavioral Risk Factor Surveillance System SAS Dataset Documentation and Technical Report: 1984–2012. Survey Research Group, Public Health Institute, 2013. [27] Bottorff JL, Bissell LJL, Balneaves LG, Oliffe JL, Capler NR, Buxton J. Perceptions of cannabis as a stigmatized medicine: a qualitative descriptive study. Harm Reduct J 2013;10:2. doi: 10.1186/1477-7517-10-2. [28] Mokdad AH. The Behavioral Risk Factors Surveillance System: past, present, and future. Annu Rev Public Health 2009;30:43–54. [29] Link MW, Battaglia MP, Frankel MR, Osborn L, Mokdad AH. Address-based versus random-digit-dial surveys: comparison of key health and risk indicators. Am J Epidemiol 2006;164:1019–25. [30] Spector P. Social desirability bias. In: Michael S. LewisBeck, Alan Bryman, Tim Futing Liao, eds. The SAGE encyclopedia of social science research methods. Thousand Oaks, CA: Sage Publications, 2004. http://srmo.sagepub .com/view/the-sage-encyclopedia-of-social-science-research -methods/n932.xml
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R E V I E W
Drug and Alcohol Review (March 2015), 34, 141–146 DOI: 10.1111/dar.12207
Prevalence of medical marijuana use in California, 2012 SUZANNE RYAN-IBARRA*, MARTA INDUNI* & DANIELLE EWING Survey Research Group, Public Health Institute, Sacramento, California, USA
Abstract Introduction and Aims. The US Drug Enforcement Agency classifies marijuana as an illegal substance, yet in 22 states marijuana is legal for medicinal use. In 1996, California legalised the use of marijuana for medicinal purposes, but population-based data describing medical marijuana users in the state has not been available. Our aim was to examine the demographic differences between users and non-users of medical marijuana in California utilising population-based data. Design and Methods. We used data from the California Behavioral Risk Factor Surveillance System 2012, an annual, random-digit-dial state-wide telephone survey that collects health data from a representative adult sample (n = 7525). Age-adjusted prevalence rates were estimated. Results. Five percent of adults in California reported ever using medical marijuana, and most users believed that medical marijuana helped alleviate symptoms or treat a serious medical condition. Prevalence was similar when compared by gender, education and region. Prevalence of ever using medical marijuana was highest among white adults and younger adults ages 18–24 years, although use was reported by every racial/ethnic and age group examined in our study and ranged from 2% to 9%. Conclusions. Our study’s results lend support to the idea that medical marijuana is used equally by many groups of people and is not exclusively used by any one specific group.As more states approve marijuana use for medical purposes, it is important to track medical marijuana use as a health-related behaviour and risk factor. [Ryan-Ibarra S, Induni M, Ewing D. Prevalence of medical marijuana use in California, 2012. Drug Alcohol Rev 2015;34:141–6] Key words: epidemiology, cannabis, harm reduction.
Introduction The US Drug Enforcement Agency classifies marijuana as an illegal Schedule 1 substance with no accepted medical use. However, a statement from the American College of Physicians and an Institute of Medicine report recommend that cannabis continue to be studied and used to treat patients who do not respond to conventional treatments for certain medical conditions [1]. In the USA, 22 states and the District of Columbia have legalised herbal medical marijuana from dried parts of the plant, Cannabis sativa. California was the first state in the nation to legalise medical marijuana. The Compassionate Use Act of 1996 (Proposition 215) added a section to California’s Health and Safety Code approving the use of herbal medical marijuana when recommended by a physician for a serious medical condition or ‘for any other illness for which marijuana provides relief’.
Marijuana contains over 400 compounds, and 66 compounds are defined as cannabinoids due to their carbon structure. Tetrahydrocannabinol and cannabidiol are the most commonly studied cannabinoids and have pharmacological effects, such as appetite stimulation, muscle relaxation and anti-inflammatory effects [2,3]. Evidence from randomised controlled trials suggests that cannabinoids can improve quality of life by improving sleep, increasing appetite and reducing chronic pain for people with chronic conditions [4,5], especially when these conditions do not respond to conventional treatments [1]. Some evidence indicates an enhanced quality of life, including improved well-being, for users of medical marijuana with chronic diseases [6,7]. In spite of the evidence that marijuana can be a useful medicine, it also carries physical and mental health risks. Regular or habitual marijuana smoking can have deleterious effects on lung health and is positively
Suzanne Ryan-Ibarra MPH, MS, Research Scientist, Marta Induni PhD, Research Program Director, Danielle Ewing MPH, Research Associate. Correspondence to Ms Suzanne Ryan-Ibarra, Survey Research Group, Public Health Institute, 1825 Bell Street, Suite 102, Sacramento, CA 95825, USA. Tel: 916 779 0115; Fax: 916 779 0265; E-mail: [email protected] *SRI and MI contributed equally towards this work. Received 10 February 2014; accepted for publication 14 August 2014. © 2014 Australasian Professional Society on Alcohol and other Drugs
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associated with chronic bronchitis and airway inflammation [8]. Previous studies have found that marijuana use is positively associated with depression, panic attacks, psychosis, schizophrenia and suicidal ideation [9–15]. One recent study using data from the US National Vital Statistics System’s Mortality Detail Files observed that states where medical marijuana was legal had lower rates of suicide among young men [16]. It is unclear what mechanism explains the observed lower rates of suicide, although the authors speculate that prior studies that found positive associations between suicidal ideation and marijuana use could reflect reverse causation due to self-medication [16]. Prior studies have described characteristics of medical marijuana users in California who have applied for medical marijuana licenses, but none have used population-based surveillance data to describe users [17]. This report summarises results from populationbased health surveillance of medical marijuana use among adults in California. To our knowledge, population-based surveillance data on medical marijuana use among adults in California has not been available before. Methods The California Behavioral Risk Factor Surveillance System (CA BRFSS) is part of the BRFSS, which is an ongoing, cross-sectional telephone survey of the noninstitutionalized US civilian population age 18 years and older. In 2012, CA BRFSS data were collected from a random sample of California adults with landline and cellular telephones, and interviews were conducted in English and Spanish (n = 7525). Medical marijuana use was assessed by asking, ‘Have you ever used medical marijuana for a serious medical condition?’ Participants who answered ‘yes’ were defined as having ever used medical marijuana. Those who answered ‘don’t know’ or ‘refused’ were excluded from analyses. If a participant needed more information about what was considered a serious medical condition, interviewers provided a list of conditions as defined by California Senate Bill 420 [18]. This study was approved by the California Department of Public Health’s Institutional Review Board and conforms to the provisions of the Declaration of Helsinki (as revised in Tokyo 2004). Overall prevalence of medical marijuana use was estimated. Prevalence of satisfaction with medical marijuana for treatment and reasons for use was estimated. Prevalence of medical marijuana use according to demographic and social factors was estimated using the following factors: age group, sex, race-ethnicity (nonHispanic white; non-Hispanic black or African American; Hispanic or Latino; non-Hispanic Asian, Pacific © 2014 Australasian Professional Society on Alcohol and other Drugs
Islander, American Indian, Alaska Native, or other), education and region. Age-adjusted prevalence estimates, standardised to the 2010 California standard population, are presented. Prevalence estimates were weighted and represent the California adult population according to 2010 California Department of Finance figures. Results Five percent of adults in California reported ever using medical marijuana (Table 1). Of these, most reported that medical marijuana helped treat a serious medical condition (92%), and the most commonly reported conditions were chronic pain (31%), arthritis (11%), migraine (8%) and cancer (7%). Other conditions reported include: AIDS, glaucoma, muscle spasms, nausea, stress and depression. Prevalence of medical marijuana use was higher among white adults (7%), compared with other race or ethnicity groups. Prevalence of medical marijuana use was higher among younger adults ages 18–24 years (9%), compared with middle-aged and older adults, although middle-aged and older adults still reported some medical marijuana use. Prevalence of medical marijuana use was similar for men and women (6% vs. 5%). Medical marijuana use was similar by region, with similar prevalence rates reported for those living in the Greater Northern California region (6%), compared with the San Francisco Bay Area (4%) or Southern California (4%). Adults with a high school degree or GED were more likely to have ever used medical marijuana use than adults who had completed at least some college or more (7% vs. 5%). Discussion We found that nearly one in 20 adults in California has used medical marijuana at least once, and most users believed that medical marijuana helped alleviate symptoms or treat a serious medical condition. Our results are from a large dataset that is representative of the California adult population. To our knowledge, our study is the first to publish population-based prevalence estimates of medical marijuana use in California. Our sampling strategy allows population comparisons of medical marijuana use by age, race/ethnicity and other demographic variables that previous studies have examined. Our study found that adults in California who had ever used medical marijuana were overwhelmingly satisfied with its ability to treat and manage their serious medical conditions. The most commonly reported reasons for use were chronic pain, arthritis, migraine and cancer. Similarly, other studies conducted in
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Table 1. Prevalence of medical marijuana use among adults in California (California Behavioral Risk Factor Surveillance System, 2012) Total, Ever used medical Ever used medical Age-adjusted n marijuana, n marijuana, weighted n weighted percenta Total Demographic characteristics Age 18–24 years 25–34 years 35–44 years 45–54 years 55–64 years 65+ years Sex Male Female Race White Hispanic or Latinob African American Asian, Pacific Islander or otherc Educational level Less than high school diploma or GED test High school diploma or GED test At least some college Region San Francisco Bay Area, Californiad Greater Northern Californiae Southern California Marijuana-related characteristics Did marijuana help your serious medical condition(s)? Yes Medical marijuana used for: Chronic pain Arthritis Migraine Cancer
(95% CI)
7525
350
1 078 795
5.15
(4.56–5.83)
415 824 1101 1304 1505 2376
41 50 44 76 85 54
271 674 212 171 171 897 205 569 145 653 71 831
9.28 5.52 4.39 5.20 4.64 2.19
(6.32–12.23) (3.88–7.17) (2.95–5.83) (3.82–6.57) (3.50–5.77) (1.52–2.86)
3135 4390
179 171
597 524 481 272
5.73 4.61
(4.69–6.76) (3.68–5.53)
4876 1733 342 574
251 52 21 26
623 942 235 973 61 171 157 709
7.41 3.33 5.12 4.18
(6.13–8.69) (2.34–4.31) (2.35–7.89) (2.38–5.97)
845
43
142 196
5.38
(3.31–7.46)
1373 5302
83 224
311 055 625 543
6.58 4.57
(4.96–8.20) (3.72–5.42)
1541 1508 4141
72 78 163
186 883 251 686 532 152
4.27 6.38 4.48
(2.92–5.61) (4.66–8.10) (3.62–5.35)
350
320
995 306
92.03
(88.76–95.30)
350 350 350 350
115 38 25 26
300 872 96 917 99 408 64 194
31.12 10.70 8.43 6.75
(25.28–36.96) (6.84–14.55) (4.74–12.11) (3.31–10.19)
a Weighted estimates were age-adjusted using California Department of Finance 2010 population estimates. bHispanic or Latino participants might be of any race. cAsian, Pacific Islander and Other includes Alaska Native and American Indian. dSan Francisco Bay Area includes Alameda, Contra Costa, Marin, Napa, San Francisco, San Mateo, Santa Clara, Solano and Sonoma Counties. e Greater Northern California excludes San Francisco Bay Area. CI, confidence interval; GED, General Educational Development test.
California and Canada have found that medical marijuana is frequently used to relieve pain (including chronic pain), headaches and arthritis [19–21]. In contrast to our findings, other studies have reported that cancer was one of the least common reasons for use among Canadians who use cannabis for therapeutic purposes [20]. When comparing prevalence of medical marijuana use by demographic factors, some findings were similar to prior studies, whereas others were different. Similar to previous studies, we found that those who had completed high school were more likely to report ever using medical marijuana, compared with those who had completed less or more education [17,19,20]. Our study
found similar rates of medical marijuana use among men and women (5.73% and 4.61%, respectively).This contrasts with previous studies who recruited participants at clinics and medical cannabis dispensaries, which found much higher rates of medical marijuana use among men as compared with women [17,19,20]. We found that medical marijuana has been used by adults of all ages in California, but younger adults aged 18- to 24-years-old have the highest prevalence of ever using medical marijuana. Because older age generally increases one’s risk for experiencing disease, it is surprising that those who are older do not have higher rates of ever using medical marijuana. It may be that medical marijuana is still not an accepted way to cope with © 2014 Australasian Professional Society on Alcohol and other Drugs
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diseases, such as cancer among older adults. Analyses using the National Survey on Drug Use and Health data have found that those born after 1950 have much higher rates of illicit drug use, including marijuana, as young adults [22]. Those born after 1950 were age 62 years and older in our sample, which may partly explain the very low rates of ever using medical marijuana in our study’s for those age 65 years and older in our study. As those who were born after 1950 become older, rates of ever using medical marijuana may rise due to increased acceptance of using illicit drugs, including marijuana, among this group. We found that non-Hispanic whites were more likely to report ever using medical marijuana, as compared with other racial/ethnic groups, including African Americans.This is similar to other studies conducted in California and Canada [17,20] but contrasts with others, which have found that African Americans were overrepresented [19]. Although we found that whites were more likely to report ever using medical marijuana compared with other racial/ethnic groups, we urge that this finding be interpreted cautiously. The absolute difference in prevalence between the racial/ethnic groups is less than three percentage points, which may not have much importance in practical terms. Medical marijuana use to treat serious medical conditions and recreational marijuana use are motivated by different factors. However, some medical marijuana use among California adults may be measured in surveys of drug use because the US federal government classifies it as an illegal Schedule 1 substance. Survey participants who are medical marijuana users may answer ‘yes’ to questions about using marijuana in these surveys. National Survey on Drug Use and Health 2010–2011 estimates that 10% of adults ages 26 and older in California used marijuana in the past year, which is double our overall estimate of medical marijuana use. Among young adults age 18–25 years old in California, 33% reported using marijuana at least once in the previous year [23]. This is more than three times the rate of ever using medical marijuana our study observed among young adults age 18 to 24 years old. Why are these results important? Our study contradicts commonly held beliefs that medical marijuana is being overused by healthy individuals by collecting data from a representative, population-based sample of users and asking them why they use medical marijuana. The CA BRFSS is a random-digit-dial telephone survey of a populationbased, representative sample of non-institutionalised adults ages 18 and older. In 2012, this survey became more inclusive and began to include a sample of cellphone only households.This is important because more © 2014 Australasian Professional Society on Alcohol and other Drugs
than one-third of adults in CA live in a household that relies on cellular phones for most or all of telephone communication [24]. The results from this survey are well-recognised as accurately measuring health-related behaviours, and data from this survey have been used for the past three decades to provide information on prevalence of health-related behaviours among population groups in states and the nation [25]. Self-reported data from the BRFSS describing health behaviours benchmark to other data sources, including national surveys that collect data via in-person interview [25]. Weighting techniques adjust for non-response so that prevalence estimates accurately reflect the population of the state [25,26]. Unlike other studies that have described characteristics of users using purposive samples of users at clinics or cannabis-focused organisations [17,20,21], our study’s population-based, representative sample of California adults allows us to generate prevalence estimates of medical marijuana use according to demographics and describe the perceived benefits and reasons for use. The most common reasons for use include medical conditions for which mainstream treatments may not exist, such as for migraines, or may not be effective, including for chronic pain and cancer. A limitation of our study is that we did not ask which symptoms medical cannabis helped users manage; for example, other studies of characteristics of medical cannabis users have asked which symptoms medical cannabis helped treat, including increasing appetite and improving sleep disturbances [19–21]. How can these results be used, and by whom? Our study’s results lend support to the idea that medical marijuana is used equally by many groups of people and is not exclusively used by any one specific group. Rather, medical marijuana is used at similar rates by men and women, young and old, high and low educated and in diverse regions throughout California. First, it is clear that Proposition 215 is helping people who are sick and use medical marijuana to treat serious medical conditions, including cancer, migraines and chronic pain, to manage their symptoms. Medical marijuana is not solely being used by young men who are accessing medical marijuana under the pretence that they have a serious medical condition and that they ‘need’ medical marijuana to treat it. A perception persists that medical marijuana users may not ‘need’ to use it to treat a serious medical condition [27]. Our study found evidence via anonymous, self-reported data that users commonly employed medical marijuana to treat serious medical conditions. Second, some people who access medical marijuana in California may not truly be using it to treat a serious medical condition. Our data
Medical marijuana in California
did not allow us to verify the self-reported diagnoses reported by medical marijuana users, but the similar prevalence rates of use among men and women, as well as by most age groups, suggest that medical marijuana is used by many groups of people. Nearly all of the people in our study who used medical marijuana reported that it helped them treat a serious medical condition. Limitations This report has limitations. First, the CA BRFSS is a telephone survey that includes only the noninstitutionalised population, so results might not apply to groups living in institutions, such as nursing homes and long-term care facilities [26]. Second, the CA BRFSS is conducted only in English and Spanish and excludes those who do not speak those languages well enough to participate in a survey [26]. Third, participating in the CA BRFSS is voluntary, and response rates for telephone surveys, including the BRFSS, have been steadily declining over the past few decades [28,29]. However, the CA BRFSS attempts to mitigate this by using weighting to adjust for non-response and adding a random-digit-dial cell phone sample to the random-digit-dial landline sample [25,26]. Fourth, CA BRFSS data are self-reported [26] and subject to social desirability bias. Social desirability bias occurs when people respond to questions in a socially acceptable manner and tends to occur for questions that are socially sensitive [30]. Even though medical marijuana is legal in California, questions about ever using medical marijuana may qualify as socially sensitive due to the stigma around using it [27] and because it is classified as an illegal Schedule I substance by the US federal government. If this bias affected responses to our study’s question, responses to ever using medical marijuana would be underreported and therefore, our reported prevalence estimates would be biased towards the null. Conclusions Our results highlight that medical marijuana is commonly used to treat serious medical conditions, including cancer, migraines and chronic pain, among California adults. Our study points out that Proposition 215 allows legal access to medical marijuana among California adults, and the group that reports ever using medical marijuana is diverse and composed of many age, gender, education and racial/ethnic groups. Therefore, it is surprising that stigma continues to be experienced by those that utilise medical marijuana. Even though those who are younger and white are more likely to report ever using medical marijuana than their older
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or non-white counterparts, our study shows that medical marijuana is used by a diverse population and is not limited to any specific age, gender, racial/ethnic or education group. Proposition 215 allows access to medical marijuana for many people, some of whom may not truly need medical marijuana, but many of whom probably do. The law benefits the sick, but also may allow for expanded legal use among young people, as observed in the higher prevalence of ever using medical marijuana among young adults in our study. Additional research should be conducted to determine predictors or correlates of medical marijuana use using population-based data. Furthermore, future research should evaluate whether rates of use according to condition vary according to demographic characteristics. Such research could be used to target medical marijuana use by demographics and serious medical condition, particularly when medical marijuana is known to be an effective treatment for certain serious medical conditions. Acknowledgements We would like to recognise and thank the participants in the 2012 CA BRFSS. This study would not have been possible without their valuable time and willingness to share personal information. References [1] American College of Physicians. Supporting research into the therapeutic role of marijuana. American College of Physicians Position Paper [Internet]. 2008. Available at: http:// www.acponline.org/advocacy/where_we_stand/other _issues/medmarijuana.pdf (accessed October 2012). [2] Grant I, Cahn BR. Cannabis and endocannabinoid modulators: therapeutic promises and challenges. Clin Neurosci Res 2005;5:185–99. [3] Pertwee RG. The diverse CB1 and CB2 receptor pharmacology of three plant cannabinoids: delta9tetrahydrocannabinol, cannabidiol and delta9tetrahydrocannabivarin. Br J Pharmacol 2008;153: 199–215. [4] Lynch ME, Campbell F. Cannabinoids for treatment of chronic non-cancer pain; a systematic review of randomized trials. Br J Clin Pharmacol 2011;72:735–44. [5] Zajicek JP, Hobart JC, Slade A, Barnes D, Mattison PG, on behalf of the MUSEC Research Group. Multiple sclerosis and extract of cannabis: results of the MUSEC trial. J Neurol Neurosurg Psychiatry 2012;83:1125–32. [6] Aggarwal SK, Carter GT, Sullivan MD, et al. Characteristics of patients with chronic pain accessing treatment with medical cannabis in Washington State. J Opioid Manag 2009;5:257–86. [7] Fiz J, Durán M, Capellà D, Carbonell J, Farré M. Cannabis use in patients with fibromyalgia: effect on symptoms relief and health-related quality of life. PLoS ONE 2011; 6:e18440. García AV, editor. [8] Joshi M, Joshi A, Bartter T. Marijuana and lung diseases. Curr Opin Pulm Med 2014;20:173–9. © 2014 Australasian Professional Society on Alcohol and other Drugs
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[9] Bovasso GB. Cannabis abuse as a risk factor for depressive symptoms. Am J Psychiatry 2001;158:2033–7. [10] Fergusson DM, Horwood LJ, Swain-Campbell N. Cannabis use and psychosocial adjustment in adolescence and young adulthood. Addiction 2002;97:1123–35. [11] Zammit S, Allebeck P, Andreasson S, Lundberg I, Lewis G. Self reported cannabis use as a risk factor for schizophrenia in Swedish conscripts of 1969: historical cohort study. BMJ 2002;325:1199. [12] Henquet C, Krabbendam L, Spauwen J, et al. Prospective cohort study of cannabis use, predisposition for psychosis, and psychotic symptoms in young people. BMJ 2005; 330:11. [13] Zvolensky MJ, Bernstein A, Sachs-Ericsson N, Schmidt NB, Buckner JD, Bonn-Miller MO. Lifetime associations between cannabis, use, abuse, and dependence and panic attacks in a representative sample. J Psychiatr Res 2006;40:477–86. [14] Rey JM, Sawyer MG, Raphael B, Patton GC, Lynskey M. Mental health of teenagers who use cannabis. Results of an Australian survey. Br J Psychiatry 2002;180:216–21. [15] Moore THM, Zammit S, Lingford-Hughes A, et al. Cannabis use and risk of psychotic or affective mental health outcomes: a systematic review. Lancet 2007;370:319–28. [16] Anderson DM, Rees DI, Sabia JJ. Medical marijuana laws and suicides by gender and age. Am J Public Health 2014;e1–8. doi: 10.2105/AJPH.2013.301612. [17] O’Connell TJ, Bou-Matar CB. Long term marijuana users seeking medical cannabis in California (2001–2007): demographics, social characteristics, patterns of cannabis and other drug use of 4117 applicants. Harm Reduct J 2007;4:16. [18] California Department of Public Health. Compassionate Use Act—Medical Marijuana Program [Internet]. Available at: http://www.cdph.ca.gov/programs/MMP/Pages/Compas sionateUseact.aspx (accessed October 2012). [19] Reinarman C, Nunberg H, Lanthier F, Heddleston T. Who are medical marijuana patients? Population characteristics from nine California assessment clinics. J Psychoactive Drugs 2011;43:128–35. [20] Walsh Z, Callaway R, Belle-Isle L, et al. Cannabis for therapeutic purposes: patient characteristics, access, and reasons for use. Int J Drug Policy 2013;24:511–6.
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[21] Lucas P. It can’t hurt to ask; a patient-centered quality of service assessment of Health Canada’s medical cannabis policy and program. Harm Reduct J 2012;9:2. [22] Substance Abuse and Mental Health Services Administration. Results from the 2012 National Survey on Drug Use and Health: Summary of National Findings. Rockville, MD: Substance Abuse and Mental Health Services Administration. Report No.: 13-4795, 2013. [23] Substance Abuse and Mental Health Services Administration. 2010–2011 National Survey on Drug Use and Health: Model-Based Prevalence Estimates (50 States and the District of Columbia). Rockville, MD: Substance Abuse and Mental Health Services Administration, March 2012. [24] Blumberg SJ, Ganesh N, Luke JV, Gilbert Gonzales MHA. Wireless Substitution: State-level Estimates from the National Health Interview Survey, 2012. Methods [Internet]. 2011. 2013. Available at: http://198.246.124.29/nchs/ data/nhsr/nhsr070.pdf (accessed May 2014). [25] Pierannunzi C, Hu SS, Balluz L. A systematic review of publications assessing reliability and validity of the Behavioral Risk Factor Surveillance System (BRFSS), 2004–2011. BMC Med Res Methodol 2013;13:49. [26] Ryan-Ibarra S, Induni M, Zuniga M, Ewing D. California Behavioral Risk Factor Surveillance System SAS Dataset Documentation and Technical Report: 1984–2012. Survey Research Group, Public Health Institute, 2013. [27] Bottorff JL, Bissell LJL, Balneaves LG, Oliffe JL, Capler NR, Buxton J. Perceptions of cannabis as a stigmatized medicine: a qualitative descriptive study. Harm Reduct J 2013;10:2. doi: 10.1186/1477-7517-10-2. [28] Mokdad AH. The Behavioral Risk Factors Surveillance System: past, present, and future. Annu Rev Public Health 2009;30:43–54. [29] Link MW, Battaglia MP, Frankel MR, Osborn L, Mokdad AH. Address-based versus random-digit-dial surveys: comparison of key health and risk indicators. Am J Epidemiol 2006;164:1019–25. [30] Spector P. Social desirability bias. In: Michael S. LewisBeck, Alan Bryman, Tim Futing Liao, eds. The SAGE encyclopedia of social science research methods. Thousand Oaks, CA: Sage Publications, 2004. http://srmo.sagepub .com/view/the-sage-encyclopedia-of-social-science-research -methods/n932.xml
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