Prescription Stimulants and the Risk of Psychosis: A Systematic Review of Observational Studies

Stimulants can cause psychotic symptoms at high doses and with parenteral use, but it remains uncertain whether the clinical use of prescription stimulants (PS) at therapeutic doses precipitates psychosis or influences long-term psychosis risk. Although serious, psychosis is a relatively uncommon event that is difficult to detect in brief randomized controlled trials. There have been several large-scale observational studies of PS and psychosis risk, which have not been reviewed; therefore, we conducted a systematic review of observational studies of PS and psychosis risk in adults and children.

We conducted a systematic review according to Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. The protocol was registered with International Prospective Register of Systematic Reviews (CRD42021243484). Eligible studies were longitudinal observational studies, either cohort or case-control, published in English that reported on PS exposure and risk of psychotic events or disorders. Risk of bias assessments were performed with the ROBINS-I instrument.

There were 10,736 reports screened, and 8 were ultimately included (n = 232,567 patients): 4 retrospective cohort studies, 1 nested case-control study, 2 self-controlled case series, and 1 prospective cohort study. Exposure to methylphenidate (MPH) was more commonly studied than amphetamine (AMPH). In the 3 studies with lowest risk of bias, there was no effect of MPH exposure on psychosis risk, but there was evidence for increased risk with AMPH in 1 study.

We conclude that observational studies do not support a clear-cut effect of prescribed MPH on psychosis risk but that AMPH has been less well studied and may increase psychosis risk.