A drug can reduce the disability associated with treatment for Parkinson's disease, research suggests.
Parkinson's is linked to abnormal movement
Doctors at University Hospital, Toulouse, gave the drug, rasagiline, to Parkinson's patients already taking levodopa to control their symptoms.
It helped to reduce the impaired and abnormal movements which develop in most patients who take levodopa over a long period.
The research is published in The Lancet medical journal.
Parkinson's disease is a degenerative disease of the nervous system associated with trembling of the arms and legs, stiffness and rigidity of the muscles and slowness of movement.
Drugs such as levodopa, which boost levels of a brain chemical called dopamine, can improve symptoms and reduce the risk of fatal complications.
But when used over a long period the drug will begin to impair patients' movements.
Several drugs, including pergolide, pramipexole, ropinirole, entacapone and tolcapone, have been shown to reduce this problem - but with only limited success.
The French team compared the effect of using rasagiline and entacapone alongside levodopa in a study of 687 Parkinson's patients recruited from centres in Israel, Argentina and Europe.
Both drugs reduced the length of time each day that patients suffered from impaired movement.
But while entacapone must be given several times a day, rasagiline is effective when administered just once a day.
The drug appeared to be safe, and was particularly well tolerated by older people.
Dr Carl Clarke, from the University of Birmingham, said the fact that rasagiline came as simple oral dose made it easier to use than most other additional therapies for Parkinson's.
He said the drug could also be safely used in combination with other drugs used to treat Parkinson's, called dopamine agonists.
These drugs mimic the effect that dopamine has on the nervous system.
They are often used so people can delay starting to take levodopa, but are not as effective.
Robert Meadowcroft, of the Parkinson's Disease Society, said Parkinson's patients reacted differently to different drugs.
Rasagiline would provide a new option, which may suit some patients better than the alternatives, he said.
He also highlighted fact that the drug was taken as a single daily dose which made the whole process easier.
"The research suggests this is a step forward for patients with positive results in the simplification and increased effectiveness of drugs for them," he said.
"Parkinson's disease is a complex condition necessitating a complex drug regime for many patients, so we welcome the study."