A daily pill could help to give a good night's sleep to thousands of Britons - and their long-suffering partners - by managing the common disorder which causes heavy snoring, scientists believe.

Researchers have started trials for a pill to help to manage obstructive sleep apnoea syndrome (OSA), a condition that causes people to stop breathing intermittently during sleep, often making them excessively tired and moody.

About one in 20 middle-aged men and one in 50 women lose sleep because of severe forms of OSA, which occurs when the upper airway becomes narrow as the muscles relax naturally during sleep. This reduces oxygen in the blood and impairs restful sleep, although the sufferer may not wake up fully.

The pill, known only by the code-name BGC20-0166, is a combination of two existing drugs that work by affecting areas of the brain associated with increased muscle tone and air-flow in breathing.

In a study involving 39 OSA patients, participants received a placebo, one of the two drugs that make up the new compound, or one or two doses of BGC20-0166 daily for 28 days. The apnoea-hypopnea index - a measure of the frequency and severity of breathing pauses during sleep - was recorded in overnight studies after 14 days and again after 28 days.

These showed that the high-dose combination of the drug reduced the symptoms of OSA by an average of 40 per cent, with patients suffering no obvious side-effects. Three of the ten patients in the high-dose group had a 50 per cent reduction in symptoms and were considered to have responded completely to treatment.

The drug is being developed by BTG, a life sciences company based in London, Philadelphia and Osaka. Thomas Roth, director of the Sleep Disorders and Research Centre at the Henry Ford Hospital in Detroit and an adviser to BTG, said: "The results from this trial demonstrate the potential of this pharmacotherapy to decrease sleep apnoea in some patients and to normalise it in others.

"Future research is needed to more precisely define the role of BGC20-0166." Current treatments for the syndrome include breathing masks worn during sleep, known as continuous positive airway pressure devices (CPAP), which have recently been approved for use on the NHS for sufferers of severe OSA.

Michael Polkey, a specialist in sleep and respiratory medicine at the Royal Brompton Hospital, southwest London, said that the initial results of the drug study were encouraging.

"This the first drug therapy that may have an effect without changing sleep architecture," he said. "A variety of existing drugs reduce the quantity of REM sleep and thus, since OSA is often worse in REM, also reduce symptoms. The magnitude of effect was not enormous so CPAP will remain the first choice but if in larger studies the results are confirmed it may have a place as an adjunctive therapy for milder patients or those who are intolerant of CPAP."

Marianne Davey, director of the British Snoring and Sleep Apnoea Association, said that previous drugs had been found to have similar results but had not helped OSA in the long term. "I believe, at the moment, the consensus is that there is no drug therapy that would be completely successful in treating OSA," she said.