People who use meth and similar drugs have a far greater risk of developing Parkinson's disease, according to new Canadian research that seems to confirm a long-held suspicion in the medical community.

Over the course of 16 years, Toronto's Centre for Addiction and Mental Health pored over nearly 300,000 California hospital records. The research showed that patients who were hospitalized for conditions linked to the use of methamphetamine or amphetamine had a 76 per cent greater chance of developing Parkinson's.

The neurodegenerative disease causes tremors, slowness and stiffness and impairs balance.
Lead researcher Dr. Russell Callaghan, from the Centre for Addiction and Mental Health, said the link has been suspected for decades, but the new data offers confirmation.

"This study provides evidence of this association for the first time, even though it has been suspected for 30 years," Callaghan said in a statement.

Parkinson's disease occurs when not enough dopamine — a chemical produced by the brain — is generated. Previous animal-based studies have shown amphetamine use causes damage to the part of the brain responsible for dopamine production.

According to the California hospital records, which accounted for data between 1990 and 2005, nearly 40,500 people who were at least 30 years old were admitted to hospital for disorders linked to meth or other amphetamine use.

That group was compared to a group of nearly 208,000 who were hospitalized for appendicitis and no documented addictions and with a second group of more than 35,000 who were admitted for conditions linked to cocaine use.

The research found only the amphetamine group had an increased chance of developing Parkinson's.

Methamphetamine and other stimulants in its category are the second most common group of illicit drugs.

Establishing the link between Parkinson's and amphetamines has been a difficult task, the researchers said, because the disease typically sets in during a patient's middle age or later years, and finding evidence would require tracking those with amphetamine addiction over the course of many years.

Researchers stressed that the controlled use of amphetamines, under the watch of a medical professional, was not included in the study as the amount used to treat many conditions is typically less than the amount involved in recreational drug use.

"It is important for the public to know that our findings do not apply to patients who take amphetamines for medical purposes, such as attention deficit hyperactivity disorder (ADHD), since these patients use much lower doses of amphetamines than those taken by patients in our study," Dr. Stephen Kish, a co-author, said in a news release.