TORONTO - Abuse of methamphetamines and other amphetamine-like stimulants is associated with a greater risk of developing Parkinson's disease, Canadian scientists said Tuesday.
Meth users can end up in hospital for a range of health issues, including heart problems, stroke and drug overdoses, and researchers at the Centre for Addiction and Mental Health in Toronto made use of the medical records of these patients in California for their study.
They wanted to see if they had a higher risk of Parkinson's disease compared to a control group -- in this case, people hospitalized for appendicitis.
After two years of working on the project, they did indeed find an association -- a 76 per cent higher risk of developing the degenerative disease characterized by tremors, rigidity and difficulty with movement.
"The bottom line is that methamphetamine users have an increased risk of Parkinson's disease in comparison to a population proxy control group," said Russell Callaghan, co-author of the study appearing in the journal Drug and Alcohol Dependence.
"People with appendicitis can be from all walks of life and they can all have different health statuses, so we just chose that one condition as a proxy, as a control group for normal."
The results suggest that if 10,000 people with meth dependence were followed for a decade, 21 would develop Parkinson's disease compared with 12 out of 10,000 from the general population.
The team used medical records for 40,472 people in California who had been hospitalized for abusing meth- or amphetamine-like stimulants from 1990 to 2005.
They were compared to records for 207,831 people admitted for appendicitis.
In addition, they were compared to 35,335 patients diagnosed with cocaine use disorders because of similar drug-using lifestyles.
"We were concerned that there may be environmental factors other than drug use that might play a role in Parkinson's disease. So Parkinson's disease, we don't really know what the cause is. We know that there are environmental factors involved. There's some genetic factors.
"So we needed to match methamphetamine users with other drug users -- with other stimulant users -- and so we chose cocaine users and we found that methamphetamine users had much higher risk of developing Parkinson's disease in comparison to cocaine users."
Diagnoses of Parkinson's disease were identified using hospital records or death certificates.
Meth and other amphetamine-type stimulants are believed to be the second most widely used class of illicit drugs in the world. They speed up the mind, there's a euphoria and a rush and a feeling of pleasure when using them, Callaghan said. During withdrawal, there can be a negative mood and tiredness.
Researchers have long suspected that abuse of these drugs could predispose users to develop Parkinson's disease, which is a dopamine deficiency neurological disorder.
"It's been known for many years that in animals, methamphetamine is associated with damage to the dopamine-producing cells. So what's been less clear is how important that is in humans," said Dr. Jon Stoessl, director of the Pacific Parkinson's Research Centre.
Commenting on the new research, he said that for the overwhelming majority of people with Parkinson's, there's no evidence that they've been exposed to illegal drugs.
"However, it does raise the point that maybe they're exposed to other toxins in the environment unwittingly," Stoessl, a neurologist, said from Vancouver.
"If one drug can do it, or two drugs can do it, maybe there are other things out there that could cause damage to the dopamine cells, so it is still an important issue."
Callaghan and his co-author made a point of saying their research is not applicable to people taking amphetamine-type prescriptions.
"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, also a CAMH scientist, said in a statement.
