Introduction: Cannabis is the most widely used illicit drug worldwide. As societies reconsider the legal status of cannabis, policy makers and clinicians require sound knowledge of the acute and chronic effects of cannabis. This review focuses on the latter.
Methods: A systematic review of Medline, PubMed, PsychInfo, and Google Scholar using the search terms "cannabis," "marijuana," "marihuana," "toxicity," "complications," and "mechanisms" identified 5,198 papers. This list was screened by hand, and papers describing mechanisms and those published in more recent years were chosen preferentially for inclusion in this review.
Findings: There is evidence of psychiatric, respiratory, cardiovascular, and bone toxicity associated with chronic cannabis use. Cannabis has now been implicated in the etiology of many major long-term psychiatric conditions including depression, anxiety, psychosis, bipolar disorder, and an amotivational state. Respiratory conditions linked with cannabis include reduced lung density, lung cysts, and chronic bronchitis. Cannabis has been linked in a dose-dependent manner with elevated rates of myocardial infarction and cardiac arrythmias. It is known to affect bone metabolism and also has teratogenic effects on the developing brain following perinatal exposure. Cannabis has been linked to cancers at eight sites, including children after in utero maternal exposure, and multiple molecular pathways to oncogenesis exist.
Conclusion: Chronic cannabis use is associated with psychiatric, respiratory, cardiovascular, and bone effects. It also has oncogenic, teratogenic, and mutagenic effects all of which depend upon dose and duration of use.