Researchers have identified a strange side effect to a treatment for Parkinson's disease: excessive gambling. Some patients taking medications known as dopamine agonists developed the problem within three months of starting treatment, even though they had previously gambled only occasionally or never at all. "This is a striking effect," remarks J. Eric Ahlskog of the Mayo Clinic, a co-author of the new study. "Pathological gambling induced by a drug is really quite unusual."

Ahlskog and his colleagues identified gambling problems during routine clinic visits for 11 patients who suffer from Parkinson's disease, a degenerative disorder in which neurons in the brain region called the substantia nigra slowly die off. The neurotransmitter dopamine helps regulate movement and balance. In addition, it is active in the brain's reward system and helps mediate the rewards brought on by gambling. All of the patients in the new study were using dopamine agonists, compounds that mimic the behavior of the neurotransmitter in the brain, as part of their treatment regimes. In addition, eight of the patients were also taking the medication carbidopa/levodopa, which is a standard therapy for Parkinson's that replenishes dopamine levels in the brain. The researchers report in the current issue of the Archives of Neurology that their newly-developed gambling problems cost patients upwards of $100,000 and, in the case of one patient, led to the break-up of her marriage.

The scientists report that the good news is that only a small number of patients exhibit the compulsive gambling side effect. In addition, it is reversible and thus poses no reason to avoid these therapies, they say. When the patients tapered off use of the troubling medications, the desire to gamble compulsively also disappeared. "I'd want patients to be very forthcoming with their doctors about their gambling," says study co-author M. Leann Dodd. "If you recognize this association early, you can possibly prevent financial ruin or destruction of relationships."