Importance: Despite evidence that individuals with a cannabis use disorder (CUD) are at elevated risk of psychosis and that the neurotransmitter dopamine has a role in psychosis, the mechanism linking cannabis use and psychosis remains unclear.

Question: Is cannabis associated with the same midbrain dopamine pathway involved in psychosis?

Findings: In this cohort study including 61 individuals, participants with cannabis use disorder exhibited increased neuromelanin–magnetic resonance imaging signals in specific voxels of the substantia nigra/ventral tegmental area (SN/VTA). This subregion has previously shown elevated signals associated with untreated psychotic symptoms.

Meaning: Increased dopamine functioning in the SN/VTA may be associated with the risk of psychosis in people with cannabis use disorder.