Cannabis products with high concentrations of delta-9-tetrahydrocannabinol (THC) are associated with users developing cannabis use disorder (CUD) and schizophrenia, according to a new systematic review published in Annals of Internal Medicine.

Researchers reviewed the effects of highly concentrated products containing at least 5 mg THC or more than 10% of the chemical per serving. High-concentration THC products were positively associated with people developing psychosis or schizophrenia (70%) and CUD (75%) in studies that did not investigate the potential of the drug for treatment of medical conditions.

“The findings are concerning and warrant a precautionary approach to using cannabis products, particularly for those with preexisting psychosis,” said Jonathan Samet, MD, professor of epidemiology and environmental and occupational health at the Colorado School of Public Health in Aurora, Colorado, and an author of the study.