A contraceptive pill that may reduce the risk of breast cancer and heart disease and eliminate periods could be available within the next five to 10 years.
Scientists believe the development could transform the lives of millions of women and would be safer than current forms of oral contraception, which carry a higher risk of breast cancer and heart problems.
The new Pill could also bring an end to the problem of premenstrual syndrome and other painful gynaecological conditions such as endometriosis.
But experts warned that progress on developing the new contraceptive is being hampered by political pressure from pro-life groups and the Bush administration in the US, who object to the fact it works in the same way as the so-called abortion pill.
At a conference to mark the 50th anniversary of the development of the Pill this year, Professor David Baird, emeritus professor of reproductive endocrinology at the University of Edinburgh, revealed that his team was testing the new compound on small groups of women in clinical trials.
Three other teams - in Sweden, Chile and the US - are also working on similar projects involving the same class of compounds.
The current combined Pill, which is taken by more than two million women in the UK, uses oestrogen and progesterone to stop ovulation and prevent pregnancy. But oestrogen can increase the risk of breast cancer and cardiovascular problems such as deep vein thrombosis.
Studies have shown that women who take the Pill have a 24 per cent increased risk of breast cancer, although scientists have pointed out that only a tiny number more will be diagnosed with the disease as a result.
A progesterone-only Pill is available and is used by 1.4 million women in Britain, but is less effective, has to be taken within a more rigid timeframe and, according to some research, may also carry a slightly higher risk of breast cancer because of the hormone it contains.
The new class of Pill that is being developed contains neither hormone but involves compounds called Progesterone Receptor Modulators (PRMs).
PRMs block the production of the progesterone hormone which prepares the body for conception and helps to maintain pregnancy. Because the compound does not contain oestrogen or progesterone and actually blocks the latter hormone, Dr Baird believes the risks of breast cancer and heart problems will be reduced.
The new Pill also stops periods altogether, in contrast to the current versions which mimic menstruation with bleeding each month.
Dr Baird said the compound had been tried on two groups of 90 women with "positive" results and few side effects, although more research was needed.
"If you could develop a pill which significantly reduces the risk of breast cancer, it would be a bestseller," he said. "It is possible that it could also stop PMS (premenstrual syndrome), which affects millions of women and results in a lot of morbidity and time off work.
"Although we have got effective oral contraceptives at the moment, they are not ideal or perfect."
Professor Baird said that a PRM Pill would have completed development within five to 10 years, but that pharmaceutical companies appeared reluctant to manufacture and market the compound as a contraceptive because it was based on the RU486 abortion pill.Reuse content