And now - a paradox. Levodopa is the first-line treatment for Parkinson's disease, and it's generally agreed that the drug can reduce some of the distressing symptoms, especially in the earlier stages of the disease. But like any powerful drug, it comes with its own range of side effects, ranging from dyskinesia, infection, headache and nausea.
When researchers from Columbia University, New York tested the drug on 361 patients with early-stage Parkinson's, they got the results they expected. Symptoms improved, compared with those taking a placebo, and those on the more powerful doses of up to 600 mg a day started suffering from the side effects.
But when they scanned the brains of the participants, they discovered the drug was actually causing damage to nerve ends in the brain. Putting it in slightly more scientific speak, the pharmacological effects were accelerating the loss of nigrostriatal dopamine nerve terminals.
So the drug was improving the symptoms while physically damaging the brain. Researchers dismiss the possibility that the drug was having a placebo effect because it was tested against a sugar pill. And even when the researchers monitored the patients for a longer period - up to ten months after the trial period - they found that levodopa was having a positive effect on the disease, even though it might be expected to hasten Parkinson's in line with the brain damage it was causing.
Nobody can yet explain the paradox other than admitting that the brain is far more complex than drug researchers believe.
(Source: New England Journal of Medicine, 2004; 351: 2498-508).
* Another Parkinsons' drug has been under the microscope of late. This time the attention has turned to rivastigmine, usually given to later-stage sufferers with mild to moderate symptoms and who have displayed signs of dementia over the previous two years.
Researchers from Istanbul University tested it on 541 Parkinson's patients, although 131 patients had to drop out of the programme because of a reaction to the group. Those made of sterner stuff completed the trial, but 29 per cent reported nausea attacks, 17 per cent suffered vomiting, and 10 per cent had tremors.
The good news was that the patients reported a 'moderate' improvement in their symptoms - provided you forget about nausea, vomiting and tremor, presumably.