It had been feared the Pill's known tendency to increase slightly the risk of blood clots (causing strokes) and certain cancers, including those of the breast and cervix, might persist long after women had given up and reached middle or old age. The increased risk would then be more serious, because these diseases are more common at older ages.
Yesterday Valerie Beral, leader of the 25-year study, conducted among 46,000 women and published in the British Medical Journal, said: "This is good news for women. We have known for a long time that the risk of developing certain conditions is slightly increased in women taking the Pill.
"Our new figures show that by the time women who have used the Pill have been off it for 10 years, their risk of developing these conditions is similar to what it would have been if they had never taken the Pill at all."
About 3 million women are current users of the Pill in Britain and 300 million have used it worldwide. Introduced to the UK in 1961, it ushered in an era of sexual freedom for women but from the start there were fears about side-effects.
The first scare, linking it with blood clots in the legs, came in 1969 and the most recent in October 1995, also involving blood clots. In the nine months after this latest scare there were 10,000 extra abortions, taking the total number to its highest level since records began in 1969.
The current study was begun in 1968 by Clifford Kay, a Manchester GP, who collected information on all aspects of the health of women on the Pill from 1,400 general practitioners. Yesterday he said: "There are few other studies which have involved quite so many people for so long. Its findings must be reassuring. We have known for a long time about the effects of the Pill but there has always been a lurking fear that something dreadful might pop out of the woodwork after 15, 20 or even 25 years, and this study shows clearly that it hasn't."
During the study, 1,600 of the 46,000 women died. They were on average 25 when the study started and half were on the Pill. By the end, two-thirds had taken the Pill for an average of five years. The results show that among current and recent users of the Pill, deaths from stroke were 90 per cent higher and deaths from cervical cancer were 150 per cent higher than among non-users, but deaths from ovarian cancer were 80 per cent lower.
However, the actual increase or decrease in risk was small because of the small number of deaths involved - 38 from cervical cancer among women who had used the Pill compared with 13 who had never used it, and 87 deaths from cerebrovascular disease (mainly stroke) among those who had used it compared with 38 among non-users. Women who smoked as well as taking the Pill were at highest risk of stroke.
Professor Beral, director of the Imperial Cancer Research Fund's Cancer Epidemiology Unit in Oxford, said: "Because deaths in this age group are low, these excess deaths are really very small indeed."
Most of the women had used a combined Pill containing 50 micrograms of oestrogen, higher than the low-dose pills common today. Professor Beral said it was likely the introduction of the low-dose pills meant the risks had fallen even lower.
Anne Weyman, chief executive of the Family Planning Association, said it was important GPs obtained an accurate picture of women's health, so that they could prescribe the correct type of Pill. "The study is reassuring, as it supports other findings which show the risks of the Pill, when correctly prescribed, are negligible."
Toni Bellfield, the association's director of information added: "There is a widespread lack of confidence about the Pill. There's always a desire to say the Pill is bad news, and it isn't. It's a good method of contraceptive when a woman wants to use it and is properly selected. Anyone thinking of using the Pill should have their blood pressure and a good family history taken."
Deborah Orr, Review page 5