Cocaine and methamphetamine may impair a person’s moral judgment, suggests new research conducted on prison inmates.

The drugs damage the parts of the brain involved in moral processing and evaluating emotions, according to U.S. News & World Report.

The study included 131 prison inmates who regularly used cocaine and meth, as well as 80 inmates who did not use the drugs. Their brains were scanned while they made decisions requiring moral reasoning. The findings are published in Psychopharmacology.

Up to 75 percent of U.S. inmates have substance abuse problems, according to a journal news release.