Allow me to dumb it down for you: Using weed raises the chance of getting schizophrenia. Light or average use roughly doubles the risk. Heavy use multiplies it by about 4 times. Using strong weed every day multiplies it by nearly 5 times. Older studies found up to a 6-times higher risk with very heavy use. Genetic studies show a smaller increase of about 37%. In Canada after legalization, the share of new schizophrenia cases linked to problem weed use nearly tripled, especially among young men.
Sources:
•Marconi et al., Schizophrenia Bulletin (2016) — meta-analysis on dose-response risk
•Di Forti et al. / EU-GEI study, The Lancet Psychiatry (2019) — high-potency cannabis findings
•Andréasson et al., The Lancet (1987) and follow-up analyses — Swedish conscript cohort
•Vaucher et al., Molecular Psychiatry (2017) — Mendelian randomization study
•Myran et al., JAMA Network Open (2025) — Ontario population study after legalization