SYDNEY, Oct. 28 -- Medications given to patients with Parkinson's disease are behind an increase in impulsive behaviours, including problem gambling, binge eating and hypersexuality, experienced by some sufferers, an Australian study revealed on Monday.

Medicines which treat the symptoms of Parkinson's disease do so by increasing dopamine levels in the brain -- however roughly 1 in 6 patients will develop impulse-control behaviours, an outcome which previously had doctors baffled.

Now, by conducting MRI testing on 57 Parkinson's patients, researchers from the QIMR Berghofer Medical Research Institute in the Australian State of Queensland have shown that it is the brain chemistry of some of those undergoing dopamine replacement therapy which is responsible for altering their behaviour.

"We found people who developed these addictive behaviours differed in the way their brain structure interacted with dopamine-containing medication, which gave rise to the impulsive behaviour," lead researcher and St Andrews Hospital neuropsychiatrist Dr Phil Mosley said.

"None of these people had a history of addictive behaviours before diagnosis and only developed them after they began treatment with dopamine-replacement medications."

To conduct their study, Mosley and his team asked study participants to gamble in a virtual casino while they were in the MRI, giving researchers a real time readout of impulsive and risk-taking behaviour.

"By combining data from brain imaging, behaviour in the virtual casino, and the effect of dopamine-replacement medication, we were able to identify people who were susceptible to impulse-control behaviours," Mosley said.

According to Mosley there is still no way to predict which patients will develop these impulse control side effects before taking the medication, however he hopes that the findings will be adapted to better identify those who are susceptible to behavioural changes in the future.

"These disorders are often a second blow to people and their families living with Parkinson's disease. Some individuals suffer financial problems or relationship breakdowns because of these harmful behaviours," Mosley said.

By predicting the onset of such complications, "we could offer targeted education to at-risk individuals, or adapt their treatment regimen to minimise the potential harms from these therapies."