Research has suggested that drugs used to treat Parkinson's disease could lead to compulsive mental health disorders.
Scientists noted "impulse control disorders" in 13.6% of more than 3,000 patients who are being treated in the US and Canada for Parkinson's.
Some 5% of patients had problems with gambling, while 5.7% engaged in compulsive buying and 4.3% in binge eating. Sex addiction was identified in 3.5% of the group.
These disorders were more common in individuals taking drugs that enhanced the effects of the brain chemical dopamine, according to the findings published in the journal Archives of Neurology.
Low levels of dopamine affect muscle control and can cause to the tremors and rigidity that are a characteristic of Parkinson's. But dopamine is also linked to addictive or compulsive behaviour.
Some drugs are "agonists", which stimulate dopamine responses in the brain.
The study authors, led by Dr Daniel Weintraub from the University of Pennsylvania in the US, wrote: "Dopamine agonist treatment in Parkinson's disease is associated with a two to 3.5-fold increased odds of having an impulse control disorder.
"This association represents a drug class relationship across impulse control disorders."