The drug levodopa slows the progression of Parkinson's disease, despite some brain imaging evidence to the contrary.
Levodopa is the most effective treatment for Parkinson's disease, although some studies suggest that the drug might actually worsen the condition. In an attempt to settle this question, researchers for the US-based Parkinson Study Group have done a placebo-controlled trial in group of 361 previously untreated patients with early Parkinson's disease. They received either a placebo or one of three doses of levodopa for 40 weeks and, two weeks after this, had an assessment.

Those on levodopa did better than those on the placebo and the higher the dose, the better they did. This suggests that the drug slows the progression of the disease. But brain imaging studies were contradictory. Those on placebo showed a one per cent decline in dopamine-producing cells - the hallmark of Parkinson's disease - while those on levodopa showed a four to seven per cent decline. Further investigation is now needed to resolve this contradiction, the researchers say.