Is Cannabis Harmless? Focus on Brain Function

Background: The degree to which cannabis use causes long term harm to mental functioning is contentious. Objective: To determine the evidence for residual and long term effects of cannabis use on mental functions. Method: Comprehensively review human studies addressing detrimental effects on human mental and life functioning. Results: Heavy use causes immediate effects on perception, mood and sedation, but also deficits in cognitive ability. But cessation following heavy use has withdrawal effects and is associated with residual effects on cognition that may last for several weeks. Heavy use also raises the risk of impoverishment of life outcomes and a decline in socioeconomic status as well as the risk of mental health problems. Young age at the start of heavy cannabis use causes a risk of lifelong detrimental effects, and as a worst case together with genetic vulnerability exacerbate a predisposition to schizophrenia. Conclusion: Heavy regular use of cannabis that begins in adolescence heightens the risk of longterm impairment of life and mental functioning.