Researchers attempted to assess the global harms associated with marijuana use and potentially define risky marijuana use in a systematic review of systematic reviews. Forty-four systematic reviews including over 1053 diverse studies were analyzed, with an average AMSTAR 2 rating of 60.1%, indicating low to moderate quality. Harm was divided into the following three categories: mental health harm, somatic harm, and physical harm. The authors found that marijuana use, particularly frequent and heavy use, was associated with increased harms in each of the three categories with mental health harms including psychosis, schizophrenia, earlier age at onset of psychosis, bipolar disorder, depression, and anxiety; somatic harms including respiratory effects such as wheezing, shortness of breath, cough, phlegm production, and dyspnea; testicular germ cell tumor development; and various cardiovascular conditions including ischemic strokes, hemorrhagic strokes, ischemic heart disease, and thromboangiitis obliterans; cognitive impairments including memory and learning deficits; reduction in educational attainment; changes in psychomotor, executive function, attention, and concentration; as well as physical harms including increased risk of suicide ideation, suicide attempts, motor vehicle collisions, and being a victim of homicide.

While these harms are numerous and diverse, a paucity exists in the literature on what defines frequent use, quantity of marijuana consumed, and the type of products used in relation to the harms of marijuana consumption, underscoring both the need for sound scientific research and the priority of the population’s health and safety before legalization.