The possible relationship between marijuana use and mental health is complicated. The most recent meta-analysis found that there’s a significant connection between heavy marijuana use and a diagnosis of psychosis, specifically schizophrenia. This mirrored the findings of previous reviews that sought to cover only high-quality studies. Another systematic review highlighted a potentially small but statistically significant link between marijuana use and the development of bipolar disorder. Heavy users of pot are also more likely to say they have suicidal thoughts.
What makes this complicated is that it’s hard to establish the arrow of causality. Are people who smoke pot more likely to develop mental health problems? Or are people with mental health problems more likely to smoke pot?
There’s a similar issue when talking about the relationship between using pot and other substances. Some see marijuana as a “gateway” drug, leading to other substance use or abuse. Others see this as only a correlation in which people who are likely to use or abuse substances are more likely to use pot as well.