Cannabis-induced psychotic symptoms (CIPSs) have both similarities and differences with positive symptoms of schizophrenia, and it remains unclear whether CIPSs result from dopaminergic mechanisms and can be treated with antipsychotics. We report the case of a 22-year-old male patient with ultrahigh risk criteria for psychosis, who reported cannabis addiction and recurrent CIPSs. Aripiprazole 10 mg/d could totally and durably suppress CIPSs in the patient, but had no effect on the smoking level. Treating CIPSs in ultrahigh risk individuals who cannot stop or refuse stopping cannabis might fit a harm-reduction strategy by preventing transition into psychosis.