Making best guesses about pot.
One essential question about state marijuana legalization continues to dog the debate: Namely, as marijuana becomes gradually legal, how do we estimate how many people will become dependent? How can we estimate the number of cannabis users who will become addicted under legalization, and who otherwise would not have succumbed?
Back in 2011, neuroscientist Michael Taffe of the Scripps Research Institute in San Diego, writing on the blog TL neuro, referenced this common question, noting that “the specific estimate of dependence rate will quite likely vary depending on what is used as the population of interest… Obviously, changing the size of the underlying population is going to change the estimated rate….”
But change it how, and by how much? The truth is, we don’t know. We can’t know in advance. There are sound arguments for both positions: Legal marijuana will lead to increased rates of cannabis addiction because of lower price and greater availability. On the other hand, almost everybody likely to become addicted to marijuana has probably already been exposed to it, including teens.
What we can start attempting to find out with greater rigor, however, is this: How many chronically addicted marijuana users are out there right now?
In The Pathophysiology of Addiction by George Koob, Denise Kandel, and Nora Volkow (2008), the base rate of cannabis dependence was estimated to be 10.3% for male users and 8.7% for female users. Their data came from the National Survey on Drug Use and Health, and the rate is similar to common estimates for prescription stimulant addiction. The dependence rate for cigarettes is at least three times as high. However, an overall dependence rate of 9.7%, when men and women smokers are combined, is the origin of the highly contested figure of 10%.
Since then, other databases have been tapped for estimates of existing cannabis dependence. In October of 2013, using the Global Burden of Disease database maintained by the World Bank, British and Australian researchers, along with collaborators at the University of Washington in the U.S., published revised estimates in the open-access journal PLOS ONE, based on numbers from 2010. The scientists culled and pooled a series of epidemiological estimates and concluded that roughly 11 million cases of cannabis dependence existed worldwide in 1990, compared to 13 million cases in 2010. This boost can be accounted for in part by population increases.
Are these dependent users distributed evenly across the globe? They are not. The PLOS ONE paper demonstrates that marijuana use is markedly more prevalent in certain regions: “Levels of cannabis dependence were significantly higher in a number of high income countries including Australia, New Zealand, the United States, Canada, and a number of Western European countries including the United Kingdom.” High income equals high marijuana usage and dependence—“Cannabis dependence in Australasia was about 8 times higher than prevalence in Sub-Saharan Africa West.” But there may be major holes in the epidemiological database: “This is particularly the case for low income countries, where there is typically limited information on use occurring, even less on levels of use, and usually no data on prevalence of dependence.”
In conclusion, the researchers found an age and sex-standardized cannabis addiction prevalence of 0.2%. “Prevalence was not estimated to have changed significantly from 1990, although increased population size produced an increase in the number of cases of cannabis dependence over the period.”
In another 2008 study, this one published in the Journal of Clinical Psychiatry, scientists at Columbia University and the New York State Psychiatric Institute looked at a set of 2,613 frequent cannabis users, using the development of significant withdrawal symptoms as the leading indicator. About 44% of regular dope smokers experienced two or more cannabis withdrawal symptoms, while about 35% reported three or more symptoms. The most prevalent symptoms in this study were fatigue, weakness, anxiety, and depressed mood. “Over two-thirds smoked more than 1 joint/day on days they smoked during their period of heaviest use; mean joints smoked/day was 3.9. About one-fifth had primary major depression….”
Age of onset was not predictive of withdrawal symptoms in this large study. The investigators suggest that “irritability and anxiety may receive great clinical consensus as regular features of cannabis withdrawal because they are subjectively and clinically striking compared to fatigue and related symptoms.” The researchers also speculate that somatic symptoms of weakness and fatigue might be attributed to varying levels of THC, compared to the presence of other cannabinoids such as CBD. The study is further evidence supporting an “association of primary panic disorder or major depression with cannabis depression/anxiety withdrawal symptoms,” suggesting a “possible common vulnerability, meriting further investigation.”
One of the reasons this matters is because of the very tight relationship between marijuana addiction and major depressive disorder. A 2008 study of young adults in the journal Addictive Behaviors found that participants with comorbid cannabis dependence and major depressive disorder, the most commonly dependence symptom was withdrawal, reported by more than 90% of the subjects in the study. 73% of the subjects experienced four symptoms or more. After that, the most common symptoms were irritability (an underreported but significant behavioral problem), restlessness, anxiety, and a variety of somatic symptoms, including gastrointestinal problems, loss of appetite, and sleep disturbances, including night sweats and vivid dreaming. The authors, affiliated with University of Pittsburgh School of Medicine, concur with the conclusion of earlier researchers: “Given the weight of evidence now supporting the clinical significance of a cannabis withdrawal syndrome, the burden of proof must rest with those who would exclude the syndrome….”
Clearly, cannabis does not contribute to the world disease burden in the same way that alcohol, nicotine, and opiods do. However, it’s fair to say that for a minority of users, cannabis dependence causes disabilities and liabilities that are not always trivial.
Mark A. R. Kleiman, a Professor of Public Policy at UCLA and a consultant to the state of Washington on marijuana legalization, told PBS:
The couple of million who stay stoned all day, every day, account for the vast bulk of the total marijuana consumed, and thus the total revenues of the illicit marijuana industry. That's typical. The money in any drug, including alcohol, is in the addicts, not the casual users. There was a big fuss during the 80s about how much casual middle-class drug use there was and how respectable folks were supporting the markets. It's certainly true that most people who are illicit drug users are employed, stable respectable citizens. But it doesn't follow that if we could get the employed, stable respectable citizens to stop using illicit drugs, the problem would mostly go away.
