A study published in The Lancet Psychiatry has found that cannabis use is associated with higher rates of psychiatric disorders, psychosis, and addiction, particularly among young people. The research indicates that daily cannabis users who develop cannabis use disorder face a significantly elevated risk of mental health issues.
Study Findings on Cannabis and Mental Health
The study, conducted by researchers from the United States, United Kingdom, Germany, and Australia, reviewed observational and epidemiological studies, clinical trials, and experimental tests. They found a consistent association between cannabis use and increased incidence of anxiety, depression, psychosis, bipolar disorder, and suicidal behaviors.
"Cannabis use often begins in adolescence and young adulthood, when anxiety, depression, psychosis, and bipolar disorder typically first develop," the authors stated. "Young people aged in their mid-teens to mid-twenties who engage in daily cannabis use and develop a cannabis use disorder have a higher prevalence of these mental disorders."
Three-Fold Increase in Psychosis Risk
A 2024 analysis cited in the study found that cannabis users, regardless of frequency, had a three-fold increase in the incidence of psychosis. The authors noted that past research suggests THC, the psychoactive compound in cannabis, can exacerbate psychotic symptoms and may induce psychosis in susceptible individuals.
"There is a consistent association between the frequency and duration of cannabis use and psychosis risk, and a causal relationship is biologically plausible," the researchers wrote. However, they noted that evidence for anxiety and depressive disorders was less clear.
Impact of Legalization on Addiction Rates
A separate review in The Lancet examined international cannabis policies over the past 25 years, finding that legalization in Canada and the U.S. led to increased rates of cannabis use disorder. "Commercialized legal markets for non-medical use in Canada and the USA were associated with increased prevalence of cannabis use and cannabis use disorder in adults and increases in cannabis potency since legalization," those authors reported.
The review also linked widespread cannabis availability to higher hospital admissions for psychosis and psychotic disorders, particularly when patients had a cannabis use disorder. "Poorly regulated legal access to medical cannabis, in the absence of efficacy and safety data, could increase risk of harm," the researchers warned.
Evidence from Canada and the U.S. showed that legalization of non-medical cannabis led to an increase in hospital visits related to psychosis and psychotic events, according to the study.
