Jul 16, 2005 Economist Magazine
The Las Vegas Pill
How treatment for Parkinson's disease turned some patients into gamblers
UNEXPECTED side-effects can result from taking medication. When Pfizer tested a new angina drug, male volunteers noted an unusual consequence—they were getting frequent erections. The compound, UK-92,480, was renamed Viagra by the pharmaceutical
giant and the rest, as they say, is history. Now researchers have found that a class of drugs used to treat Parkinson's disease also has side-effects, albeit of a less desirable nature. It causes a small but significant number of patients to become
compulsive gamblers, alcoholics, gluttons and sex pests.
Parkinson's disease occurs when the brain cannot make enough of a neurotransmitter called dopamine. Dopamine carries signals to the parts of the brain that control the initiation and co-ordination of movement. A shortage of dopamine in the brain can lead to tremors, slowness of movement, loss of balance and muscle rigidity. Although there is no cure for the disease, a class of drugs called dopamine agonists mimic the effects of dopamine and bring some relief to patients, particularly in the early stages of the disease.
However, researchers at the Mayo Clinic in Rochester, Minnesota, have discovered that dopamine agonists have the power to change the personality of some patients. In a study published online in the Archives of Neurology, they found that a small but
significant number of patients, most of whom had never or only occasionally gambled before, took up the habit. Others became compulsive eaters or alcoholics, or developed an increased sex drive that their spouses found bothersome. Fortunately for the
patients and their families, the penchant for indulging in compulsive behaviour disappears soon after stopping the medication. Unfortunately, the same is not true for the Parkinson's symptoms.
The drug fingered as having the biggest association with compulsive behaviour is called pramipexole, which strongly stimulates a dopamine receptor located in the part of the brain believed to be involved in the control of emotional matters.
Over-stimulation of this area can cause compulsive behaviour.
In a parallel, retrospective study, it was found that 1.5% of patients taking pramipexole became pathological gamblers. Because of the rarity of the side-effect, the Mayo Clinic researchers say there is no reason to stop prescribing the drug. However, in light of this research, doctors prescribing pramipexole should warn patients of the risk, and patients and their families should be alert to any changes in behaviour. Meanwhile, who wants to bet on how long it will be before a crooked casino boss is caught adding dopamine agonists to the bar drinks?
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