Hassle-free contraceptive pill for men being developed by scientists

Taken every day, the hormone-free contraceptive would also have no long-term effect on a man's fertility.

The tablet will be welcomed by women worried about the hormone-laden female version's links to breast cancer and fatal blood clots.

It could also allow couples to share the responsibility for contraception – a role that traditionally falls to women, who could in future have to decide whether to trust their partners.

Allan Pacey, a male fertility expert at Sheffield University and secretary of the British Fertility Society, said: "Anything that could be taken at home every day as a pill and would change the production or quality of sperm very quickly without changing hormones is a good thing."

Cautioning that the drug would not protect against sexually-transmitted infections such as chlamydia, Dr Pacey said it was most likely to appeal to those in a committed relationship.

He added: "A bigger concern is whether women would trust their men to take it.

"The evidence suggests they would. There are a number of studies that show most women are trusting of their partners when they are in a stable relationship.

"It comes back to this probably only being a contraceptive that is appropriate for men in a relationship."

Some women will be reluctant to trust their partners to take their tablets regularly because men, not being able to get pregnant, will have less motivation.

Rebecca Findlay, of the Family Planning Association, said: "The two choices available for men are the condom and vasectomy.

"The development of a male pill would be very exciting and really useful for a lot of relationships."

So far, the drug, which is known as CDB-4022, has been tested only on animals, but human trials are expected to start soon.

The research, which is funded by the U.S. government, showed that the drug quickly blocks sperm production.

Sperm counts fell sharply within a week of male monkeys being given the contraceptive.

Levels had fallen to such a low level inside three weeks that the animals were considered infertile.

Crucially, sperm levels quickly returned to normal after the drug was stopped, suggesting it does not have a long-lasting effect on fertility.

In addition, hormone levels, and so libido, were not affected and the monkeys did not suffer any visible side-effects.

The development of male contraceptives has been dogged by sideeffects such as hot flushes, moodswings and low sex drive, caused by hormones in the drugs affecting the body's own hormonal balance.

Sheri Hild, a researcher on the project, said: "It was a beautiful study.

"Sperm counts went down to a level considered infertile and came back up on their own.

"And it didn't have any effects on hormones such as testosterone, so we are very excited about it."

Dr Hild, of U.S. research firm Bioqual, now plans to carry out longerterm studies, in which the animals will be mated with females to confirm the drug actually prevents pregnancy.

She envisages the drug being a once-a-day-pill for men.

While it might be possible to formulate it into a weekly tablet, users are less likely to forget a daily pill.

The pill is one of several male contraceptives being developed by companies eager to claim a share of the £21billion spent each year around the world on the female pill.

Many of the drugs being developed, however, are based on hormones and carry the risk of unwanted side-effects.

In addition, they are mainly being developed as injections, implants and patches, rather than pills.

The Bioqual researchers, working with scientists from Pittsburgh and Illinois universities, looked at the effect of CDB-4022 on sperm production in monkeys.

Some of the creatures were given the drug for a week, while others were given a dummy compound.

Tests showed the sperm count quickly dropped among those given the contraceptive, with the animals judged infertile 17 days after the treatment started.

Four months later, the animals' fertility had returned to normal, a U.S. conference on the future of male contraception was told.

It is thought the drug blocks a crucial stage in sperm development, in which immature sperm are 'nursed' and nourished by other cells known as Sertoli cells.

The extensive testing needed to ensure the drug is both safe and effective for use in men means it is several years from the market.

■The one-a-day male pill is made from a synthetic compound originally developed as an antihistamine.

It has never been used to treat allergies and researchers hope it will come into its own as a contraceptive instead.

It is thought to work by blocking an early stage in sperm development in which immature sperm are fed by other cells.

Mature sperm are not affected by the pill and men would have to use an alternative method of contraception for the first few weeks until these sperm were used up or reached the end of their short lifespan.

The compound has fewer side-effects than most contraceptive drugs because it does not alter hormone levels.