CHICAGO -- There are some warnings that a popular drug used for Parkinson's disease could be linked to compulsive gambling.

Researchers at the Mayo Clinic report in the July issue of Archives of Neurology that some patients using the drug Mirapex or similar medications developed an addiction to gambling.

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"This is a striking effect," said Dr. J. Eric Ahlskog, a Mayo Clinic neurologist who treated most of the patients in the study. "Pathological gambling induced by a drug is really quite unusual."

The main author said 11 Parkinson's disease patients developed the unusual problem between 2002 and 2004, four of whom had never gambled before starting the treatment. Another 14 patients have been identified with the same problem since then.

"Most of the time, the patient came in for a routine exam and would sheepishly admit, 'I've been gambling too much,' or family members would mention that their loved one had been gambling excessively, that this behavior was totally out of character for them, and that the gambling was causing problems in their lives," said Dr. M. Leann Dodd, a Mayo Clinic psychiatrist who led the study.

One patient lost more than $100,000 as well as her first marriage due to her compulsive gambling. She could never drive by a casino without going in, and each time she shopped for groceries, she was compelled to purchase multiple scratch-off lottery tickets.

Six of the patients developed additional behavioral problems simultaneously with the pathological gambling, including compulsive eating, increased alcohol consumption, increased spending and hypersexuality. The problems went away as the gambling subsided.

Doctors who weren't involved in the Mayo study also reported a similar problem with some of their Parkinson's disease patients.

A retired government intelligence worker in California said his gambling problem began when he was on Mirapex and that it stopped when he stopped using the drug.

"It's a very rare side effect and reversible if you get off the drug, but you have to make the association," Ahlskog said in a news release.

"When our neurologists tapered the patients off the medication, several reported a dramatic resolution of their problem," Dodd said. "One patient said it was 'like a light switch going off.'"

The researchers said the the problem does not occur frequently and that most people treated with Mirapex or similar medications experience no such effect. They said the potential gambling side effect would not be a reason to stop prescribing it. Instead, researchers urge Parkinson's disease patients taking the medications to be very candid about gambling problems that may arise after starting the medication.

"I'd want patients to be very forthcoming with their doctors about their gambling," Dodd said. "If you recognize this association early, you can possibly prevent financial ruin or destruction of relationships."

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