Heavy Methamphetamine, Marijuana Users at Increased Risk of Schizophrenia

People hospitalized for methamphetamine or marijuana use are more likely than those being treated as inpatients for other substance use disorders to develop schizophrenia, according to a new study.

Researchers examined medical records of patients admitted to California hospitals over a 10-year period with a diagnosis of dependence or abuse for methamphetamine, marijuana, cocaine, opioids or alcohol, HealthDay reports. The study included 42,412 people in the methamphetamine group, and 23,335 in the marijuana (cannabis) group.

Patients hospitalized for dependence on methamphetamine and who had never been diagnosed with schizophrenia or psychotic symptoms at the beginning of the study were 1.5 to three times more likely to be diagnosed with schizophrenia over the course of the study, than patients who used cocaine, alcohol or opioids. The risk of schizophrenia in methamphetamine users was similar to the risk seen in heavy marijuana users, the researchers report in the American Journal of Psychiatry.

“We really do not understand how these drugs might increase schizophrenia risk,” researcher Dr. Stephen Kish said in a news release. “Perhaps repeated use of methamphetamine and cannabis in some susceptible individuals can trigger latent schizophrenia by sensitizing the brain to dopamine, a brain chemical thought to be associated with psychosis.”