A handful of drugs that are commonly prescribed for Parkinson's disease can convert a tiny fraction of patients into compulsive gamblers in as little as a month, according to a study published today in the journal Archives of Neurology.
The study is one of several to show the link and confirms that the drug pramipexole -- widely prescribed under the brand name Mirapex -- is the most likely to cause the rare side effect.
Dr. M. Leann Dodd, a psychiatrist at the Mayo Clinic in Rochester, Minn., and her colleagues studied 11 patients who became compulsive gamblers -- nine of whom were taking pramipexole. Two others took a similar drug, ropinirole.
Some of the patients gambled away up to $1,500 a day, the study found. Losses over a six-month period ranged from $2,500 to $200,000.
Dodd emphasized that pramipexole and other drugs were beneficial for improving mobility and alleviating the uncontrolled trembling associated with Parkinson's disease.
"People need to understand that this is a pretty unusual condition," she said. "These are still very effective treatments for Parkinson's disease."
Dr. Mark Stacy, a neurologist at Duke University Medical Center in Durham, N.C., who previously studied a different group of compulsive gamblers, noted that researchers had studied compulsive gambling in fewer than 30 patients and cautioned against raising unnecessary alarm.
About 30% of Parkinson's patients take the drugs that have been linked to compulsive gambling, Stacy said.
"These drugs have helped hundreds of thousands of patients," said Stacy, who estimated that 1% of Parkinson's patients develop problems with compulsive gambling.
But Dodd said the research highlighted the need for patients to overcome their embarrassment and flag early signs of destructive behavior.
"We want people to talk to their neurologist in the event they experience strange behavior," she said.
Dodd's study found that when patients were started on pramipexole or ropinirole, or when their dosages were increased, uncontrollable gambling followed within three months in most cases.
When dosages were decreased or discontinued, behavior typically returned to normal at least as quickly, the study showed.
One patient in the study described the effect as being "like a light switch being turned off."
Parkinson's disease is a neurological disorder that impairs physical mobility, typically producing uncontrolled trembling, stiffness and slowness of movement.
The main cause is believed to be a shortage of the chemical dopamine in the part of the brain known as the substantia nigra. There is no known cure.
The drugs linked to gambling are dopamine agonists and work by mimicking the function of dopamine in the brain.
While they can alleviate Parkinson's symptoms, the drugs also appear to affect parts of the brain that are crucial for regulating behavior.
Some patients also exhibited abnormally increased appetites for food, alcohol and sex, the study found.
The drug levodopa, the "gold standard" for treating Parkinson's disease, was not linked to any compulsive behaviors. It is not a dopamine agonist and works by prompting the brain to create natural dopamine.
The National Institute of Neurological Disorders and Stroke estimates roughly half a million Americans have Parkinson's disease.
The National Parkinson Foundation estimates three times that number.