In a widely cited 2014 article, Nora Volkow and her colleagues at the National Institute on Drug Abuse highlighted the evidence that connects marijuana use with psychosis, anxiety, depression, and addiction.1 A second article examined its harmful effects on cognition, psychosis, and motivation.2 The American Psychiatric Association’s position statement begins, “There is no current scientific evidence that marijuana is in any way beneficial for the treatment of any psychiatric disorder.”3[PDF]
Despite near-unanimous medical warnings, marijuana use is widespread among psychiatric patients,4 including those with psychotic disorders.5 Advocates tout its benefits for anxiety, depression, and bipolar disorder6; and medical marijuana regulations in 9 states include PTSD as a qualifying condition. Psychiatry’s apprehension plainly disagrees with more favorable attitudes in patients and the public. How can psychiatrists best address their patients’ marijuana use in this contentious environment?
What follows is a critical summary of the evidence now available that connects marijuana with cognitive problems, psychosis, anxiety, PTSD, depression, and addiction. I have relied on published reviews, supplemented by PubMed searches for more recent data. Be forewarned—this is an evolving picture, since credible research about the psychiatric effects of cannabis is only now emerging after decades of legal constraint. I argue that patients benefit when psychiatrists attend to their marijuana use—a hands-off approach is likely to miss an important influence on their symptoms—and that a collaborative approach can steer between the Scylla of harsh admonition and the Charybdis of naive acceptance.
The psychopharmacology of marijuana is complex. Delta-9 tetrahydrocannabinol (THC), the most psychoactive of its many cannabinoid constituents, acts on endogenous cannabinoid receptors, which, like those for monoamines and endogenous opioids, are found in brain areas subserving memory, cognition, emotions, and motivation. Cannabidiol (CBD), another cannabinoid found in marijuana, appears to counteract the psychedelic effects of THC; it is being investigated as a treatment for a number of medical and psychiatric conditions.7 Samples of illegal marijuana these days have very low CBD:THC ratios, which maximizes psychedelic effects, while medical marijuana is advertised with CBD:THC ratios as high as 20:1.8 Thus, it may be important to understand the source and purported characteristics of the marijuana a patient is using.
Extensive laboratory, clinical, and epidemiological evidence connects marijuana use to cognitive impairment, and both clinical and epidemiological data link it to psychosis. The correlations with addiction, anxiety, and depression, however, are based mainly on interviews of national population samples, which are likely to differ from patients who present for treatment. The evidence that marijuana benefits PTSD comes mostly from animal data. Table 1 summarizes this evidence, along with treatment recommendations.
Non-intoxicated regular cannabis users perform worse on global neuropsychological tests by a third of a standard deviation or less. Some evidence suggests this cognitive impairment may be short-term, with recovery occurring over days to months after cessation of use. Its extent and persistence are worse with early age of onset, high frequency, and long duration of use.2 Marijuana-induced cognitive dysfunction may account for its association with motor vehicle accidents at a level approaching that of alcohol, as well as with reduced life achievement.1 Discussing patients’ marijuana use in high-risk situations, including driving and sexual activity, may be lifesaving, and exploring its effects on academic and work performance may improve outcomes.
For decades, marijuana has been associated with the emergence of schizophrenia and other psychotic disorders. Recent data show that in genetically vulnerable individuals, psychotic disorders are more likely to emerge and to emerge earlier if marijuana is used.2 Ongoing marijuana use by patients with schizophrenia is associated with worse outcomes.5 Thus, patients with individual or family histories of psychosis can be counseled that marijuana use puts them at greater risk for the development or exacerbation of a psychotic illness.
Dr. Woodward is Assistant Clinical Professor of Psychiatry at Boston University School of Medicine. He is in private practice in Newton, MA.
Dr. Woodward reports no conflicts of interest concerning the subject matter of this article.
1. Volkow ND, Baler RD, Compton WM, Weiss SRB. Adverse health effects of marijuana use. N Engl J Med. 2014;370:2219-2227.
2. Volkow ND, Swanson JM, Evins AE, et al. Effects of cannabis use on human behavior, including cognition, motivation, and psychosis: a review. JAMA Psychiatry. 2016;73:292-297.
3. American Psychiatric Association. Position Statement on Marijuana as Medicine. December 2013. https://www.psychiatry.org/File%20Library/Learn/Archives/Position-2013-Marijuana-As-Medicine. Accessed February 10, 2017.
4. Lopez-Quintero C, Perez de los Cobos J, Hasin DS, et al. Probability and predictors of transition from first use to dependence on nicotine, alcohol, cannabis, and cocaine: results of the National Epidemiologic Survey on Alcohol and Related Conditions (NESARC). Drug Alcohol Depend. 2011;115:120-130.
5. Foti DJ, Kotov R, Guey LT, Bromet EJ. Cannabis use and the course of schizophrenia: 10-year follow-up after first hospitalization. Am J Psychiatry. 2010;167:987-993.
6. Smoker J. Top 5 Mental Conditions Treated With Marijuana. The Weed Blog. August 12, 2011. https://www.theweedblog.com/top-5-mental-conditions-treated-with-marijuana. Accessed February 10, 2017.
7. Welty TE, Luebke A, Gidal BE. Cannabidiol: promise and pitfalls. Epilepsy Curr. 2014;14:250-252.
8. How to interpret the CBD & THC ratio results? Alpha-Cat. http://www.alpha-cat.org/resources/understand-and-interpret-the-cbd-thc-ratios. Accessed February 10, 2017.
9. Twomey CD. Association of cannabis use with the development of elevated anxiety symptoms in the general population: a meta-analysis. J Epidemiol Community Health. 2017 Jan 4. [Epub ahead of print].
10. Mizrachi Zer-Aviv T, Segev A, Akirav I. Cannabinoids and post-traumatic stress disorder: clinical and preclinical evidence for treatment and prevention. Behav Pharmacol. 2016;27:561-569.
11. Degenhardt L, Hall W, Lynskey M. Exploring the association between cannabis use and depression. Addiction . 2003;98:1493-1504.
12. Blanco C, Hasin DS, Wall MM, et al. Cannabis use and risk of psychiatric disorders: prospective evidence from a US national longitudinal study. JAMA Psychiatry. 2016;73:388-395.
13. Copeland J, Pokorski I. Progress toward pharmacotherapies for cannabis-use disorder: an evidence-based review. Subst Abuse Rehabil. 2016;7:41-53.
14. Gates PJ, Sabioni P, Copeland J, et al. Psychosocial interventions for cannabis use disorder. Cochrane Database Syst Rev. 2016;5:CD005336. ❒