Methamphetamine Abuse Linked to Parkinson's Disease

Deborah Brauser

July 29, 2011

July 29, 2011 — Abuse of methamphetamine or other amphetamine-type drugs (meth/amphetamine) significantly increases the risk of developing Parkinson's disease (PD), new research suggests.

In a new retrospective cohort study of more than 280,000 patients, those hospitalized for meth/amphetamine dependence or abuse had a significantly higher risk for a PD outcome than did 2 matched control groups, including one consisting of cocaine users.

"We found that meth/amphetamine users had a 76% increased risk of developing PD," write lead study author Russell C. Callaghan, PhD, from the Dalla Lana School of Public Health at the University of Toronto, Ontario, Canada, and the Center for Addiction and Mental Health, and colleagues.

The investigators note, however, that the findings "might not at all relate to those individuals who take much lower doses of amphetamine drugs for therapeutic purposes," including attention-deficit/hyperactivity disorder.

Dr. Nora D. Volkow

Commenting for Medscape Medical News, Nora D. Volkow, MD, director of the National Institute on Drug Abuse, said that until recently, no studies have given any preliminary evidence that individuals taking methamphetamines were at this greater risk for PD.

"This study is important because this information needs to go to the public so they are aware of the potential adverse effects of drugs that they may be exposed to. The findings are relevant as a message on prevention to try to protect people from something that is very toxic," said Dr. Volkow.

"For clinicians, I think they should screen for past history of methamphetamine use, especially when they are evaluating for the early stages of [PD]," she added.

The study was published online July 26 in Drug and Alcohol Dependence.

Widespread Use

The investigators note that meth/amphetamine stimulants are the second most widely used class of illicit drugs worldwide.

Previous animal research, dating back 30 years, has shown these agents damage dopaminergic neurons. As a result, "researchers have long speculated that these drugs may predispose users to develop PD, a dopamine deficiency neurological disorder."

Last year, as reported by Medscape Medical News, the same group of investigators published a study suggesting that a small number of meth/amphetamine users older than 50 years may be at risk of developing PD.

For this study, linked data from California inpatient episodes and death records from January 1990 to December 2005 were assessed for patients older than 30 years admitted for meth/amphetamine abuse (n = 40,472), as well as for 2 age- and sex-matched comparison groups: 1 made up of appendicitis patients (n = 207,831) and the other of cocaine abusers (n = 35,335).

An appendicitis-based cohort was chosen because the condition is a relatively frequent reason for inpatient admission and can yield a sufficiently large sample, whereas the other comparison cohort was selected because both cocaine and methamphetamine users experience similar health effects, explain the researchers.

Subjects were followed up for up to 16 years.

Results showed a significantly increased risk for PD for the meth/amphetamine group compared with both the appendicitis (hazard ratio [HR], 1.76; P = .014) and cocaine groups (HR, 2.41; P = .004).

There was no significant PD risk found for patients in the cocaine group vs those in appendicitis group.

"The findings of our epidemiological study might seem to be at variance with the apparent absence of any 'epidemic' of PD in methamphetamine users that is obvious to the public or to caregivers," write the investigators.

"This could be explained in part by the relatively low incidence of both conditions in the population and also by the likelihood that prior use, such as a young adult, would not typically be considered by treating physicians as a possible cause of PD in the late middle-aged patient," they add.

Screening Essential

Dr. Volkow, who was not involved in the research, noted that clinicians are often uncomfortable asking about substance use in their patients.

"This is true for alcohol or nicotine and even less probable for these other substances. But without that screening, we'll never be able to really understand how drugs can impact other diseases."

The limitations of the study included its retrospective nature and the fact that history and severity of abuse were not reported.

"It would have been valuable to know if someone had been taking methamphetamines for 2 months vs 5 or 10 years. I would hope that that important variable would be examined in future studies."

She also noted that it would have been interesting if the investigators had examined nicotine use.

"Nicotine has been shown to be neuroprotective for [PD] in some studies. I would have liked for the investigators to have looked at that interaction to see if the risk was greater in patients who consumed less nicotine but were taking methamphetamines," said Dr. Volkow.

"Between this and their earlier study, along with a new one by other investigators that has not been published yet with similar findings, it makes me believe that indeed there is an increased risk associated with Parkinson's and methamphetamine abuse. But we need others to look at this in greater detail so we can get an idea about how significant this risk is."

The study was funded indirectly by an institutional grant from the Ontario Ministry of Health and Long-Term Care to the Center for Addiction and Mental Health. The study authors and Dr. Volkow have disclosed no relevant financial relationships.

Drug Alcohol Depend. Published online July 26. Abstract

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