Abusing methamphetamine or other stimulant drugs can increase the risk of developing Parkinson’s disease, new research suggests.

Scientists compared three groups: 40,000 people hospitalized because of abuse of methamphetamine or amphetamines, 207,000 people not addicted to drugs who were admitted to the hospital for appendicitis and 35,000 people admitted for cocaine-use disorders. They found patients with methamphetamine or amphetamine-use disorders were 76 percent more likely than the other two groups to develop Parkinson’s disease, HealthDay reports.

According to the article, the findings translate into 21 out of 10,000 people with methamphetamine or amphetamine dependence develop Parkinson’s over 10 years, compared with 12 out of 10,000 people without this drug dependence.

Lead researcher Dr. Russell Callaghan from the Center for Addiction and Mental Health in Toronto, said in a news release, “This study provides evidence of this association for the first time, even though it has been suspected for 30 years.” He said that Parkinson’s disease is a result of low levels of the chemical dopamine in the brain, and that animal studies have shown that methamphetamine damages the brain’s dopamine-producing regions.

The authors emphasized the findings do not apply to people who take amphetamines for medical purposes, such as attention-deficit hyperactivity disorder (ADHD), because these people use much lower doses of amphetamines than those used in the study.

The study appears in the journal Drug and Alcohol Dependence.