Pathological behaviors provoked by dopamine agonist therapy of Parkinson's disease.

The dopamine agonist medications, pramipexole and ropinirole, are commonly used to treat Parkinson's disease. These two drugs have a highly specific affinity for cerebral D3 receptors, known to be localized to the mesolimbic system. Herein is described a common side effect of these drugs, encountered in our routine clinical practice: pathological behaviors. This includes excessive gambling, hypersexuality, shopping, hyperphagia or obsessive hobbying, which may develop in up to 30% of people taking higher agonist doses. In contrast, treatment with the dopamine precursor, levodopa, in the absence of D3 agonist therapy very rarely provokes such behavioral syndromes. Although these agonist-induced behaviors have been called "impulse control disorders", the problem is not simply loss of impulse control, but rather a novel obsessive-compulsion directed at one or a few behaviors, often taking on pathological proportions. This experience points to the dopamine D3 receptor as a potential therapeutic target for gambling, sex or other addictions occurring spontaneously in the general population.