How the contraceptive works: graphic

A NEW generation of contraceptive medication that guards against breast cancer as well as pregnancy could be available within five years, scientists predicted yesterday.

Patient trials of a drug that is used in higher doses to cause abortions have shown it to be an effective contraceptive with few side-effects, and animal and cell models have even suggested that it can protect against breast tumours.

Women taking the new Pill, which contains no female hormones, would have no periods and would thus be unlikely to suffer from pre-menstrual syndrome (PMS). The contraceptive is also thought to carry a lower risk of blood clots than existing varieties.

If the early results are confirmed by larger studies, the research, led by the University of Edinburgh, would provide millions of women with a safe, reliable way of controlling fertility. While the Pill is the most effective form of contraception, many are put off by side-effects from the female hormones on which it is based.

About 3.5 million British women — approximately a third of those of reproductive age — take the Pill, more than 90 per cent of whom are on the combined form that contains oestrogen and progesterone, the two female hormones. The rest take the mini-Pill, which contains progesterone only. Its popularity has largely recovered from the 1995 scare that prompted hundreds of thousands to give up oral contraception after “third-generation” Pills that contain different kinds of progesterone were linked to a higher risk of thrombosis.

The combined Pill protects against ovarian and endometrial tumours, but its oestrogen content is thought to contribute to a slightly increased risk of breast cancer. While the mini-Pill does not have this drawback, it is less effective and has other side-effects such as heavy bleeding. The new Pill works on a completely different principle, using a chemical called mifepristone to block the action of progesterone, which the body needs to ovulate and support a pregnancy.

As it contains no oestrogen it should not promote breast cancer, and by inhibiting progesterone it is thought that it may even reduce the risk. It is also unlikely to cause other hormonal side-effects, and has the added benefit of stopping periods, which should prevent PMS.

Mifepristone, also known as RU486, is licensed for use in abortions, though it is used at doses 100 times lower for contraception. David Baird, Professor of Reproductive Endocrinology at the University of Edinburgh, said that this could be the biggest obstacle to bringing it to the market, as anti- abortion activists have vociferously objected to it.

“If it was decided just on scientific grounds, and the pharmaceutical industry did not respond to all sorts of irrational factors, it could be developed within five years,” he said. “As it is, I would expect it to be within five to ten years.”

Mifepristone works by binding to progesterone receptors, so that the body cannot respond to the hormone. If given in high doses when a woman is pregnant, it causes miscarriage, but smaller doses can prevent ovulation and conception. Two trials, each involving about 90 women in Scotland, South Africa, China and Nigeria, have now shown that it is well tolerated with few side-effects, and is at least as effective as conventional Pills.

The effect on breast cancer is predicted because some kinds of breast tumour appear to be sensitive to progesterone, so blocking its action should inhibit their growth. “Certain breast cancer studies suggest that progesterone can promote cancer as well as oestrogen,” Professor Baird said. “There are also some preliminary clinical data on women with advanced breast cancer which suggests that this could be helpful.”

Anna Glasier, Professor of Sexual and Reproductive Health at the University of Edinburgh, said: “If we can come up with a Pill that reduces the risk of breast cancer, we will all be taking it, whether or not we need contraception.”

BIRTH CONTROL

• The Pill was introduced in Britain in 1961 for married women only. It is now used by 3.5 million women in Britain and 85 million worldwide
  
• More than 90 per cent of British users take the combined pill. This works by manipulating hormone levels to prevent ovulation. The mini-pill thickens cervical mucus to prevent sperm from reaching the womb
  
• Oestrogen in the combined pill is thought to account for a slightly higher incidence of breast cancer. Five users in every 100 get breast cancer, compared to four in 100 non-users
  
• Another rare complication is deep-vein thrombosis, at about three deaths per million users. Side-effects are bloating, breast tenderness and, for the mini-pill, excessive bleeding

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