"These patients identified these behaviors as being uncharacteristic of their baseline behavior," said Maryellen Dodd, the Mayo Clinic psychiatrist who led the research. "Nearly all the patients who came to our attention had never gambled or gambled very infrequently."
All 11 patients were taking a dopamine agonist drug. In nine cases the drug was pramipexole, sold under the brand name Mirapex. In two cases, it was ropinirole, sold as Requip.
"This may be happening because pramipexole is highly selective for the receptors in the brain called the dopamine D3 receptors," Dodd said. "Those D3 receptors are highly concentrated in the limbic areas of the brain associated with emotions, behavior, reward, pleasure, and mood."
Seven patients developed pathological gambling habits within one to three months of treatment. Four others began compulsive gambling 12 to 30 months after starting the therapy.
At least six patients also developed other problems, including compulsive eating, increased alcohol use, and hypersexuality. At least one patient developed an obsession with pornography and engaged in extramarital affairs.
The drug levodopa, which is used more commonly than dopamine agonists to treat Parkinson's, was not linked to any compulsive behaviors. It works by prompting the brain to create natural dopamine.
An estimated 30 percent of Parkinson's patients take dopamine agonists. Researchers say that the gambling side effect occurs in only a small number of those patients.
Discontinuing or reducing the dose of the drug appears to curb the compulsions. It took most patients less time to return to normal than to develop the gambling habits.
"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."
However, scientists emphasize that the dopamine agonists improve mobility and alleviate the trembling associated with Parkinson's disease.
"These are unusual cases," Dodd said. "Many patients are being nicely treated with these medications, so we would not want them to discontinue the medication without discussing this with their neurologists."
Instead, the scientists say, the research highlights the need for patients to identify early signs of gambling and other destructive behavior.
"The gambling was reversible, sometimes with dramatic resolution after stopping the drug," Dodd said. "This is an unusual problem but important to publicize, because recognition of this [problem] is crucial, since it is reversible."
"Patients are encouraged to be very open with their physicians regarding behaviors that may be out of character for them," she added. "And physicians are encouraged to adequately inform patients of the possibility of these problems when prescribing the medications."
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