Researchers at the Mayo Clinic in Rochester, NY, have found a link between drugs used to treat symptoms of Parkinson’s disease and compulsive gambling, eating, drinking and sexual activity in patients with the disease. In a study published online Monday by the Archives of Neurology, researchers said that between 2002 and 2004 they identified 11 Parkinson’s patients at the clinic who reported sudden, inexplicable changes in personality and behavior after starting drug therapy. Since then they have identified an additional 14 patients who were not included in the original study.

Most often the behavior started within months of taking the drug Mirapex, the most commonly prescribed drug for Parkinson’s. Other drugs linked to the behavior include Requip and Permax. Parkinson’s in a slow, degenerative nervous system disorder caused when people do not make enough dopamine, a messenger chemical that carries information through the area of the brain that controls movement.

Many Parkinson’s drugs are dopamine agonists, compounds that mimic the behavior of dopamine in the brain in order to control symptoms. Dopamine plays a key role in the pleasure and reward area of the brain. When it goes awry, people can develop serious addictions.

Compulsive behavior has been seen to stop once the drug is discontinued for a length of time. In one case, a 52-year old man began gambling daily, gained 50 pounds from compulsive eating, and engaged in numerous extramarital affairs. Paul Sanberg, distinguished professor of neurosurgery and director of the University of South Florida Center for Aging and Brain repair, said that the fact that patients were able to reduce the behavior by stopping drug therapy “implies that it was the drug” that caused the compulsive behavior.

Mirapex is manufactured by Boehringer-Ingelheim Pharmaceuticals, Inc., and was approved for sale in the U.S. in 1997. A class-action suit was filed against the company last year because of its link to compulsive behavior in patients. The company insists there is no scientific evidence that Mirapex causes compulsive behavior, but it has revised patient insert literature to include compulsive behavior among the drug’s potential side effects.

Sources: Josephine Marcotty, “Parkinson’s drugs linked to gambling, other compulsions,” Star Tribune, July 12, 2005; “Parkinson’s Treatment Linked to Compulsive Gambling,” ScientificAmerican.com, July 12, 2005; Amanda Gardner, “Some Parkinson’s Drugs May Trigger Compulsive Gambling,” HealthDay, July 11, 2005.