The world's first contraceptive pill that frees women from menstruation and its associated stomach pains and mood swings will be launched in Britain early next year.

A woman on the pill normally takes it for 21 days, then takes nothing, or a dummy tablet, for the next seven days. During this time she has a monthly bleed that is usually much lighter than for a woman not on the pill. However, the new pill, Lybrel, is the first designed to be taken all year round without a break.

'The drug has been developed for women who find the current need to stop taking the pill for one week every month inconvenient, and for those who suffer from the hormonal fluctuations to which this can contribute,' said Ginger Constantine, vice-president of Women's Health Care and Bone Repair at Wyeth pharmaceuticals, the pill's US-based manufacturer.

Lybrel is a 'combined pill', which means it contains both oestrogen and progestogen, by far the most common type of oral contraceptive in the UK.

Critics warn that oral contraceptives raise the risk of blood clots and breast cancer. They are also concerned that continuous exposure to hormones might damage women's fertility. But Wyeth claims the new pill is safe. 'Our findings show that 99 per cent of the 187 women in our studies began their periods within three months of stopping taking the pill,' said Constantine.

There is no medical reason why women cannot take any contraceptive pill continuously. But when the oral contraceptive was launched in the Sixties it was thought that retaining a monthly bleed would help to make it more acceptable to women. Surveys in the Seventies reinforced that belief, with women saying it made the process feel normal.

Since then attitudes have changed. Although Lybrel is the first pill designed to be taken continuously, the only difference between it and pills already on the market is that the dose will be varied so it can be taken non-stop.

'It is completely safe to suppress menstruation for years at a time,' said Toni Belford, director of information at the fpa, formerly the Family Planning Association. 'It is not natural for women to have as many periods as they do now. A few generations ago women would have had virtually no periods for years at a time because they would have spent all their child-bearing years either pregnant or breastfeeding.'

Belford said she expected some women would be keen to stop their menstrual cycle, while others would continue to choose the reassurance of a regular bleed.

Wyeth hopes to have its US and European licence applications granted by the end of the year.