Drugs giant SmithKline Beecham revealed on Monday that its drug ropinirole, sold as Requip, was as effective as the standard treatment, levodopa, but was much less likely to cause side effects like shaking.

Doctors say levadopa relieves the symptoms of Parkinson's.

Karen Allen reports: "Those using the alternative were 15 times less likely to suffer side-affects"

But long-term use can cause severe involuntary movements which, for some, are worse than the condition itself.

Parkinson's, which ironically is characterised by shaking as well as muscle stiffness and slowness of movement, is a progressive neurological condition whose sufferers include film star Michael J. Fox and Muhammed Ali.

It can affect all aspects of a person's life and occurs when cells in the part of the brain which controls movement are lost.

It affects one in 500 people in the UK.

Ropinirole was licensed by the US' Food and Drug Administration in 1997.

The BBC's Toby Sealey: "It is hoped doctors will now rethink the way they treat the disease"

SmithKline Beecham said its five-year trials were conducted in the UK, Europe, Israel and Canada.

They involved 268 patients who were in the early stages of Parkinson's.

Actor Michael J Fox also suffers from the disease

They showed that treating patients with Requip at the outset, and using levodopa only when symptoms become bad enough to require the stronger drug, resulted in fewer involuntary body movements than using levodopa from the beginning.

Currently levodopa is initially given to patients, with roprinole offered as an add-on treatment for those with advanced symptoms.

Side effects worse than disease

Parkinson's is believed to be caused by the death of nerve cells that normally produce dopamine, a brain messenger chemical that plays a key role in controlling movement.

Enoch Powell battled Parkinson's for many years

There is no known cure, but drugs such as levodopa - a generic drug developed in the late 1960s which is converted into dopamine in the body - can control the symptoms.

Patients typically get good symptom relief after beginning use of the drug, but then require ever-increasing amounts of the drug to achieve the same benefits, which can lead to side effects.

Requip is one of a new class of drugs called dopamine agonists, which mimic the effects of dopamine without actually creating more of the messenger chemical.