The Psychiatric Consequences of Cannabinoids.

With rising rates of cannabis use in the general population and an increasing number of US states legalizing both recreational and medical cannabis use, it is important to be informed about the adverse consequences of cannabinoids. This Commentary provides an overview of the psychiatric effects of plant-based and synthetic cannabinoids, differentiating acute effects from effects associated with persistent use. Cannabinoids produce multiphasic and dose-dependent effects on anxiety, mood, and perception, in addition to impairing cognition and psychomotor function. Generally, in healthy individuals, the acute negative psychiatric effects of cannabinoids are rated as milder in severity compared with those in individuals with pre-existing psychiatric disorders. With chronic exposure to cannabinoids, the probability of developing tolerance and dependence can increase. A problematic pattern of cannabis use can lead to clinically significant impairment and distress. Cessation of cannabis use in individuals who are tolerant and dependent can lead to a withdrawal syndrome. Studies report long-term cannabis exposure has been linked to psychiatric disorders, such as anxiety, psychotic and mood disorders. Limitations to the existing evidence notwithstanding, the plausibility of a causal relationship between cannabinoid exposure and persistent negative psychiatric outcomes, and the potential for long-term brain changes by regular exposure, especially for adolescents, are sufficient to warrant discussions with clinicians and the public. Implications for clinicians who certify, prescribe, or care for patients receiving cannabinoids are discussed, and a case is made for further research to better understand the impact of legalization on public mental health.