Parkinson's disease patients who take the drug ropinirole 24-hour prolonged release can extend the time before the drug wears off and symptoms return.
This is a development from the immediate release ropinirole which does not prevent the return of symptoms for as long.
Researchers from the American Academy of Neurology carried out tests of prolonged release ropinirole on 393 Parkinson's sufferers, half of whom were given a placebo. Both groups took levodopa.
It was found that those taking prolonged release ropinirole had an additional 2.1 hours before symptoms returned compared to an extra 0.3 for those who were taking the placebo.
Over half the group taking the drug were classified as much improved or very much improved after the course of testing. They were also able to reduce their levodopa dosage.
Rajesh Pahwa, lead author of the study, said: "Ropinirole 24-hour prolonged release, when taken with levodopa, is effective in reducing daily 'off' time [time after which the drugs have worn off] for Parkinson patients who aren't getting the best results from levodopa.
"We also found the drug helped improve quality of life and motor function."
The 24-hour prolonged release drug is thought to have fewer side effects and be as effective as the immediate release version.