By Ania Lichtarowicz
BBC News health correspondent
The oral contraceptive pill may protect women from heart disease and some cancers, scientists suggest.
Oestrogen in the Pill could offer protective benefits
The research, presented to the American Society for Reproductive Medicine (ASRM) meeting in Philadelphia, involved more than 160,000 women.
It found the risk was lowest for women who had taken the Pill for over a year.
The Wayne State University, Detroit, study contradicts previous research which suggested the Pill increased the risk of those conditions.
However, the Detroit study - one of the largest ever done into the Pill's long term effects - shows the overall risk of developing heart disease was about 10% lower in women who've taken the pill for at least a year.
The research suggests that the Pill is particularly protective against heart attacks, angina and mini strokes and cuts the risk of ovary and womb cancers.
Dr Rahi Victory, who led the research, said it could be the female hormone, found in many types of oral contraceptives, which is having a protective effect.
He said: "It is likely that oestrogen reduces the inflammation in the blood vessels.
"We know that it has an effect on a molecule called nitric oxide which has to do with healing of a blood vessel as well as having to do with stretching open the blood vessel - dilating the blood vessel as we like to call it.
"So those are both beneficial molecular level events that occur in women that take oestrogen that would contribute to preventing improving the incidence of heart disease. "
'Do not ignore risks'
Oestrogen stops blockages from building up in the arteries, which slows down the blood flow. It is these blockages that lead to heart disease,
Cathy Ross, a spokesperson for the British Heart Foundation, said: "Whilst we welcome all research that examines reduction of risk factors associated with CHD, the potentially serious risks associated with taking the contraceptive pill, such a blood clots, should not be ignored.
"It would be unwise to suggest that the pill should be taken on a regular basis to protect against CHD."
However, the protective effect of the Pill against some cancers cannot be explained.
Dr Amy Berrington, of Cancer Research UK, said the link between oral contraceptive use and cancer risk was highly complex, with studies showing that taking the Pill reduced ovarian and endometrial cancer risk, but increased the risk of breast cancer risk and probably also cervical cancer.
She added: "However, once a woman has stopped using the Pill, her risk of breast cancer falls again until, after about 10 years, her risk is the same as if she had not taken the Pill.
"An important outstanding question is how long the reductions in ovarian and endometrial cancer risks remain after women stopping taking the Pill."
A second study at the conference found coming off the Pill appeared to increase a woman's sex drive.
Researchers at the University of California studied 20 women, aged around 34, who stopped taking the Pill after six months.
Their libido increased, and they experienced less sexual dysfunction such as vaginal dryness.
The researchers suggest one in six women who are taking the Pill experience such problems.
They say not taking the Pill is linked to a rise in levels of the sex hormone testosterone and a fall in a hormone that can suppress desire.
It is also suggested that the loss of sexual desire could be linked to the elimination of ovulation, removing a natural trigger for a woman to have sex.
Dr Marian Damewood, president of the ASRM, said: "When a healthy pre-menopausal woman experiences decreased sexual function, hormonal contraception could be considered a possible cause and may be discontinued to determine if it is indeed a factor."
But a spokeswoman for the UK's Family Planning Association said lifestyle factors such as stress, financial worries, how many children you have and alcohol and drug use could all affect a woman's sex drive.