Marijuana Dependence and Legalization

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.

Who Smokes Dope, And How Much?

Marijuana stats skew perceptions of use.

Most statistical surveys of marijuana focus on a single quantitative measurement: How many people are using? But there’s a problem: More marijuana use does not necessarily translate into more marijuana users. And that’s because a clear majority of the consumption, and black market dollars, come from the heaviest smokers.

Drug policy researchers at the RAND corporation decided that frequency of use and amount of consumption were valuable parameters gone missing in most policy discussions. So they put the focus not just on use, but also on “use-days,” and pulled a number of buried tidbits from a very big data pile. If you zero in on consumption, and not just consumers, they insist, you will find a wholly different set of inferences.

For example: “Although daily/near-daily users represented less than one-quarter of past-month cannabis users in 2002 and roughly one-third of past-month users in 2011, they account for the vast majority of use-days and are thus presumably responsible for the majority of consumption,” write Rachel M. Burns and her RAND colleagues in Frontiers of Psychiatry. As with alcohol, the majority of cannabis consumption can be accounted for by a minority of users. The heaviest users, the upper 20 percent, consume 88 percent of the U.S. marijuana supply, say the RAND researchers. “Furthermore, if over time there were no change in the number of cannabis users, but the ratio of light vs. heavy users switched from 80/20 to 20/80, then consumption would increase by 250% even though there was no change whatsoever in the number of users.”

The RAND group used two data sets on cannabis consumption—the National Survey on Drug Use and Health (NSDUH) in the U.S., and the EU Drugs Markets II (EUMII) in Europe. Data included figures for past-year and past-month use, past-month use days, and past-month purchases.

Other intriguing figures come to light when you study cannabis use, as opposed to cannabis users. The researchers declared that “only 14% of past-year cannabis users [primarily males] meet the criteria for cannabis abuse or dependence, but they account for 26% of past-month days of use and 37% of past-month purchases.”

Happen to smoke blunts? That turns out to be very telling, according to the RAND study. “Perhaps the most striking contrast concerns blunts. Only 27% of past-year cannabis users report using a blunt within the last month, but those individuals account for 73% of cannabis purchases.” Casual users, it seems, don’t do blunts.

Clearly, it takes a lot of casual users to smoke as much marijuana as one heavy user. But exactly how many? The RAND researchers ran the numbers and concluded that, in terms of grams consumed per month, it would take more than 40 casual smokers to equal the intake of a single heavy user. The share of the market represented by daily/near-daily users is clearly the motive force in their analysis.

The study in Frontiers in Psychiatry also found patterns of interest on the buy side. General use took an upswing beginning in 2007. While the probability of arrest per marijuana smoking episode hovers somewhere in the neighborhood of 1 in 3,000, everything changes if you are purchasing cannabis. RAND reported that young people collectively make more purchases per day of reported use than do older users. Therefore, “statistics indicating that the burden of arrest falls disproportionately on youth relative to their share of all users may not be prima facie evidence of discrimination if making more purchases per day of use increases the risk of arrests per year of use.” Once again, those aging Baby Boomer potheads get the best deal. They have more money with which to buy bigger amounts less often, thereby greatly lessening their chances of arrest and prosecution.

This also applies to minority arrests for marijuana offenses. “Non-Hispanic blacks represent 13% of past-year cannabis users vs. 23% of drug arrests reported by those users, but they report making 24% of the buys. Thus, some of their higher arrest rate may be a consequence of purchase patterns… African-Americans may not only make more buys but also make riskier buys (e.g., more likely to buy outdoors).”

The researchers were able to draw some conclusions about the growth in marijuana usage from 2002 through 2011, based on the NSDUH data. Their main conclusion, after exploring the demographics of this 10-year record of use, is that “consumption grew primarily because of an increase in the average frequency of use, not just because of an increase in the overall number of users.”  The driver of consumption turns out to be… greater consumption. And that increased consumption is coming from… older adults. Those older adults, it turns out, are smoking more weed.

The shift is dramatic: “In 2002, there were more than three times as many youth as older adults using cannabis on a daily/near-daily basis; in 2011 there were 2.5 times more older adults than youth using on a daily/near-daily basis.” The record of alcohol and cigarette use over the same period showed no such inversion of use patterns.  And the tweeners? “In 2002, 12-17-year-olds represented 13% of daily/near-daily users; in 2011, that had dwindled to 7%.” These trends are not just the obvious result of an increase in the proportion of older adults in the population at large. Increases in the proportion of older heavy cannabis users were much greater than the general population drift.

Among the questions raised by the RAND analysis:

— Are older marijuana smokers primarily recreational, or medicinal?

—Do increased use days among older, college-educated marijuana smokers indicate greater social acceptance, or something else?

—Are younger people replacing traditional cannabis use with other substances?

—Why did Hispanic use increase more over the study period than other ethnic groups?

Burns R.M., Caulkins J.P., Everingham S.S. & Kilmer B. (2013). Statistics on Cannabis Users Skew Perceptions of Cannabis Use, Frontiers in Psychiatry, 4   DOI: 10.3389/fpsyt.2013.00138

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