ABSTRACT ~ Purpose of Review: This is a comprehensive review of the association between cannabis use and psychological disorders. It reviews the latest and seminal evidence that is available and attempts to conclude the strength of such association. Recent Findings: Cannabis is a flowering plant with psychoactive properties, attributed to cannabinoids that naturally occur within the plant. These act through the CB1 and CB2 receptors to inhibit GABA and glutamate release, as well through other forms of neuromodulation through the modulation of the endocannabinoid system (eCBs); a system that is otherwise involved in different pathways, including reward, memory, learning, and pain. Recent societal changes have increased the use of both medical and recreational cannabis. Patients with mental illness are considered more vulnerable and are prone to reward-seeking behavior. Cannabis use disorder (CUD) has been shown to have an increased prevalence in individuals with mental illness, creating an explosive cocktail. Approximately 1 in 4 patients with schizophrenia are also diagnosed with CUD. Cannabis use is associated with 2–4 times the likelihood of developing psychosis in healthy individuals. It has also been associated with multiple poor prognostic factors in schizophrenia, as well as in patients with a history of psychosis who do not meet diagnostic criteria for schizophrenia. Cannabis has been linked with anxiety; THC has been shown to elicit anxiety; however, anxiety is also a trigger for cannabis use. However, a recent large meta-analysis did not find a convincing link between cannabis and anxiety. This was reiterated in a recent epidemiological study that did not f ind such a correlation; however, it did identify a link between cannabis use, substance disorder, alcohol use disorder, drug use disorder, and nicotine dependence. Similarly, contradicting data exists regarding the link of depression and cannabis use.

SUMMARY: Cannabis use is increasing with recent societal shifts; however, its interaction with mental health is less well understood. CUD is highly prevalent in individuals with mental health disorders, especially those with other substance abuse disorders. There is evidence to support that cannabis use may trigger and worsen psychosis and schizophrenia. The link with depression and anxiety is less clear and needs further investigation. Personality disorder is linked with substance use disorder and shares similar risk factors with CUD. Psychopharmacology Bulletin. 2020;50(2):56–67.