Minneapolis, MN: Residents of states where cannabis is legal do not possess elevated rates of psychosis, and they are also less likely to exhibit symptoms of alcohol abuse, according to longitudinal data published in the journal Psychological Medicine.
A team of researchers affiliated with the University of Minnesota and the University of Colorado assessed the relationship between adult-use cannabis legalization and psychosocial functioning in a cohort of 240 pairs of identical twins. One twin resided in a jurisdiction where adult-use cannabis sales were legally permitted, while the other lived in a state where marijuana was criminally prohibited.
Investigators reported that legalization was associated with a slight uptick in the frequency with which subjects reported consuming cannabis – a finding consistent with prior studies. However, they also reported that those in legalization states were less likely to engage in behaviors associated with problematic alcohol use. That finding is consistent with prior data indicating the use of cannabis is associated with a decrease in the amount of alcohol consumed by individuals seeking alcohol treatment.
Authors further reported that legalization was not positively correlated with increased incidences of psychosis, substance abuse disorder, or other adverse outcomes.
They concluded: “Recreational cannabis legalization causes increases in mean cannabis frequency and residents of recreational states have fewer recent symptoms of AUD [alcohol use disorder]. Broadly speaking, our co-twin control and differential vulnerability results suggest that the impacts of recreational cannabis legalization on psychiatric and psychosocial outcomes are otherwise minimal. … Both sets of results are reassuring with respect to public health concerns around recreational cannabis legalization.”
Although the use of cannabis and other controlled substances tends to be more common among those with psychotic illnesses, studies indicate that lifetime incidences of marijuana-induced psychosis are relatively rare among those who do not already have a prior diagnosis of a psychiatric disease. According to one recently published study, fewer than one-half of one percent of cannabis consumers had ever reported experiencing psychotic symptoms requiring medical intervention – a percentage that is lower than the rate associated with alcohol.
Full text of the study, “Recreational cannabis legalization has had limited effects on a wide range of adult psychiatric and psychosocial outcomes,” appears in Psychological Medicine.