Cannabis and development of dual diagnoses: A literature review

Background: The use of cannabis has garnered more attention recently with ongoing efforts at marijuana legalization. The consequences of cannabis use are not clearly understood and remain a concern. Objectives: To review the acute and persistent effects of cannabis use and associations with psychiatric disorders. Methods: Using Pubmed and PsychInfo, we conducted a narrative review of the literature on cannabis and psychiatric comorbidity using the keywords cannab*, marijuana, schizo*, psychosis, mood, depression, mania, bipolar, and anxiety. Results: There is substantial evidence of cannabis use leading to other illicit drug use and of an association between cannabis use and psychosis. A few reports suggest an association with bipolar disorder while the association with depression and anxiety disorders is mixed. Conclusions: Whenever an association is observed between cannabis use and psychiatric disorders, the relationship is generally an adverse one. Age at the time of cannabis use appears to be an important factor with stronger associations observed between adolescent onset cannabis use and later onset of psychiatric disorders. Additional studies taking into account potential confounds (such as withdrawal symptoms, periods of abstinence, and other substance use) and moderators (such as age of initiation of cannabis use, the amount and frequency of drug use, prior history of childhood maltreatment, and gender) are needed to better understand the psychiatric consequences of cannabis use.