Doctors treating 120,000 sufferers of Parkinson's disease in Britain may have to change their approach after researchers identified the first drug shown to slow progress of the disease.

One of the world's largest studies of the condition, involving 1,176 patients with early stage Parkinson's in 14 countries including the UK, showed that the drug rasagiline delayed neurological deterioration. Rasagiline, whose brand name is Azilect, is already used to treat the symptoms of Parkinson's but doctors have been reluctant to prescribe it in the early stages of the disease, fearing the effects will wear off.

Research by the Mount Sinai School of Medicine in New York, published in the New England Journal of Medicine, suggests that its early prescription may be the best way to delay progress of the disease. Researchers found that after 18 months, patients who had received early treatment with 1mg of the drug daily had not deteriorated as much as those in whom treatment was delayed by nine months. The difference was small, they said, but clinically significant.