Patients taking certain drugs to treat Parkinson's disease could be damaging their heart valves, new research has suggested.
Two studies in this month's New England Journal of Medicine – one by Italian researchers and another by German doctors – highlight the risk faced by a quarter of Parkinson's patients.
The concerns focus on patients taking pergolide and cabergoline, which are sold under brands including Permax and Dostinex.
"This is an extraordinarily high risk," commented Dr Bryan Roth, a pharmacology professor at the University of North Carolina at Chapel Hill.
"It's a bad side effect. As far as I know, there are no medications that can reverse it and valve replacement surgery is the only solution."
Although Dr Roth was not involved in the study, he was among a group of scientists who warned of the effects of diet drug fen-phen on the heart, which led to it being banned in 1997.
Permax is owned by pharmaceutical company Eli Lilly and Dostinex is owned by Pfizer, which has insisted the benefits of the drug outweigh the risks.
Parkinson's is a degenerative condition affecting the nervous system and can often impair the sufferer's ability to walk, talk and write.
According to the Parkinson's Disease Society, there are around 120,000 individuals with Parkinson's and around 10,000 people are diagnosed in the UK each year.