With recreational marijuana now legal in several states and medical marijuana available in many, my patients are presenting with more questions about cannabis and its disorders. Some smoke marijuana sporadically or regularly, some are clearly addicted, and a few want help to get it under control or stop.
The DSM-5 criteria for cannabis use disorder are the same as for other addictive substances: at least two out of a possible eleven signs or symptoms within a 12-month period. Four have to do with core addiction phenomena (craving, difficulty limiting use, using more than intended, and spending a lot of time on cannabis-related activities); five with adverse consequences (unfulfilled role obligations, use despite social problems, giving up important activities to use, use in dangerous situations, and use despite a cannabis-related medical or psychological problem); tolerance; and withdrawal. (The DSM-IV dependence criteria, on which much of the research now available is based, are similar, but DSM-IV abuse was subsumed into DSM-5 use disorder; the DSM-IV dependence criteria are thus more stringent than DSM-5 use disorder.) DSM-5 includes cannabis withdrawal, requiring at least three of the following for diagnosis: irritability, anxiety, sleep problems, reduced appetite, restlessness, depressed mood, or a physical problem (abdominal pain, tremor, sweating, fever, chills, or headache); a subset of patients with recent heavy use experience these symptoms.
Deborah Hasin and her colleagues at Columbia University and the National Institutes of Health compared data on the prevalence of marijuana use disorders drawn from face-to-face interviews with a large (over 36,000) representative sample of U.S. adults in 2001-2002 and 2012-2013. In that eleven year period, past-year marijuana use increased from 4.1% to 9.5% of adults, and marijuana use disorders increased from 1.5% to 2.9 %. In 2012-2103, 30.6% of past-year users met criteria for DSM-IV marijuana abuse or dependence. The authors note that the doubled prevalence of marijuana use disorders appears to reflect more widespread use.
With such a large sample, the investigators were able to look in some detail at risk factors; here I will focus on psychiatric disorders. Since this was a population-based study, not a treatment sample, the numbers may differ for patients in clinical settings. Cannabis use was six times more common among people with any psychiatric or substance use disorder—31%. Having a mood, anxiety, personality, conduct, psychotic, or attention deficit disorder doubled the likelihood of cannabis use, while nicotine, alcohol, or cocaine dependence tripled the likelihood of use.
Among those who tried cannabis, those with psychiatric and substance use disorders had significantly higher risks of developing dependence—about twice the risk for conduct and psychotic disorders, triple for mood disorders and ADHD, and four times the risk for personality disorders. Having another substance use disorder was even more problematic: nicotine dependence tripled the risk of transition from cannabis use to dependence, alcohol dependence quadrupled it, and people with cocaine dependence had six times the risk. Interestingly, having a first-degree relative with a substance use disorder increased the risk of transition from cannabis use to dependence by a factor of 1.6.
Some may argue that cannabis use and its disorders are relatively benign, since cannabis, like nicotine, does not lead to the acute behavior problems associated with alcohol, cocaine, and opioids. Neuropharmacological addiction by itself is not necessarily a problem—millions of people are addicted to caffeine without problems. The putative benefits of marijuana are widely touted by advocacy groups and commercial advertising, and for some people, marijuana is helpful.
Still, it is important to weight the risks and benefits.
Addiction is a problem when it results in adverse medical, psychological, developmental, or social consequences. Nora Volkow and her colleagues at the National Institute on Drug Abuse looked at the evidence for adverse health effects. They found high quality evidence for reduced life achievement, motor vehicle accidents, and chronic bronchitis; and medium level evidence that marijuana contributes to abnormal adolescent brain development, schizophrenia, depression, anxiety, and progression to use of other addictive drugs.
Volkow and another group of coauthors have examined in more detail the evidence for long-term psychiatric effects of cannabis use, including negative effects on cognition, motivation, and psychosis risk. Nonintoxicated cannabis users show mild but significant decrements in executive functions, attention, learning, memory, motor skills and verbal ability, which may resolve with prolonged abstinence. The degree and persistence of impairment may depend on the age of onset, frequency, and duration of use. Since the endocannabinoid system is involved in regulation of neurodevelopment, there is concern about adolescent marijuana use disrupting brain development. The authors note that some of the observed impairment in learning and educational achievement may be the consequence of reduced motivation, which may result from cannabis itself becoming a major motivator. They found consistent evidence linking adolescent cannabis use to psychosis risk, which may result from cannabis causing psychosis, shared etiology of psychosis and marijuana use, gene-environment interactions, or self-medication of pre-psychotic symptoms. Most people who use cannabis do not develop psychotic disorders, but cannabis appears to trigger the emergence of psychosis in some vulnerable people.
Some of this picture—particularly the comparisons of marijuana with other addictive drugs—may change as marijuana’s legal status and the public perception of its risks continue to evolve. Addictions are, after all, disorders of motivation and stress response, both of which are influenced by beliefs and social interactions.
So it appears that cannabis is somewhat less addictive than nicotine, alcohol, and cocaine. But if 9% of people who try cannabis transition to DSM-IV dependence, and the risk is markedly higher those with psychiatric disorders, and nearly a third of current users are dependent, then psychiatrists can expect to see cannabis disorders in a lot of patients. We will be well advised to ask patients about their marijuana use, to evaluate whether they are addicted, and to guide them in weighing the risks and benefits of continued use. As for other addictions, there is good evidence for modest efficacy of cognitive-behavioral therapy, motivational enhancement therapy, and contingency management, and limited evidence for benefit from various psychiatric drugs.