The first trial of a male contraceptive in sexually active couples has shown it was 100 per cent effective in preventing pregnancies.

The hormonal treatment - a combination of an implant under the skin and a three-monthly injection - was used by 55 couples for one year.

The method relieved the men of the need to remember to take a daily pill - and none of their partners became pregnant. The research, by a team from Australia, is published in the Journal of Clinical Endocrinology and Metabolism.

Professor David Baird, of the Centre for Reproductive Biology at Edinburgh University, an expert on the male pill, said the finding was a significant advance.

"We do seem to be making progress to getting a male pill or some form of male contraception. This is a great addition to the literature. There will be slight alterations to the components used but it helps us on our way," he said.

Professor Baird said there were six groups around the world testing versions of a male contraceptive focused on a combination of the male hormone testosterone and the female hormone progestogen.

Trials on volunteers in the UK had shown that the hormonal combination prevented production of sperm in men, but the Australian researchers, from the Anzac Research Institute in Sydney, had been the first to show that it worked in a real situation when used by couples.

Professor David Handelsman, who led the research, said: "This shows the way for a final product to be a single injection containing testosterone and progestogen which will easily be given by local doctors on a three to four-monthly basis and still maintain sexual health."

He said it was now up to the pharmaceutical companies to develop the research into a usable product.

Two companies, Organon and Schering, announced 18 months ago that they were working to develop a male pill. It is likely to be available either as an implant or in an oral form. Professor Beard said: "We will probably get one of them through within five years."

Surveys have shown women are enthusiastic about the prospect of handing over responsibility for contraception to men - especially if protection is guaranteed by an implant.

But experts expect a male pill to find niche markets among couples in stable relationships. One likely period of high demand would be after a woman has had a baby and is still breast feeding, when the female pill is not appropriate.

The reversible treatment works by making use of the body's natural system which is involved in initiating puberty. A combination of testosterone and progestogen temporarily turns off the signals from the brain that stimulate sperm production.

The process also turns off the man's testosterone production - so he needs to be given extra doses of the hormone to keep him healthy and maintain his sex drive.

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