Oral contraceptives. Latest research.

Ever since oral contraceptives came on the market 35 years ago, questions have lingered over their safety: Do they increase the risk of stroke and breast cancer? Do they decrease libido? Two new studies and a survey have provided some answers--most of it encouraging.

Stroke is rare among reproductive-age women, and today's oral contraceptives which contain a low dose of estrogen do not appear to increase the risk. When the birth control pill first went on the market, it was associated with the risk of stroke because it contained very high doses of estrogen. Women today can choose among more than 50 brands of the birth control pill, which contain about one-fifth the estrogen of the earlier versions.

A slightly increased risk of breast cancer was found among women currently using combined oral contraceptives and those who had used them in the past ten years. This is the conclusion of a British team of researchers who analyzed 54 studies conducted in 25 countries. The combined number of participants included over 53,000 women with breast cancer and over 100,000 without the disease.

The researchers found no evidence of an increased risk of breast cancer diagnosed ten or more years after stopping the use oral contraceptives. Age appears to be a factor. The older a woman is at last use of oral contraceptives, the higher her odds of developing breast cancer. However, the cancers diagnosed among pill users tended to be less advanced than the cancers diagnosed among women who never used birth control pills.

When the birth control pill first came on the market, some researchers thought it might decrease sexual desire, but a new survey found that libido and sexual satisfaction are enhanced by one type of oral contraceptive known as the triphasic pills. Questionnaires were filled out by 364 women, aged 18 to 26 years, all sexually active and users of oral contraceptives.

Doctors not expected to find sexual desire and satisfaction increased by any version of oral contraceptives. They theorized that the reason the triphasic pills had this effect was its varying levels of one hormone, progestin. Monophasic pills, on the other hand, provide the same level of estrogen and progestin per dose for 21 days of each menstrual cycle.

The two brands used by most women in this survey, which was conducted between 1989 and 1990, were Ortho-novum 7/7/7 triphasic pills or Ortho-novum 1/35 monophasic pills.

Earlier research has shown that oral contraceptives lower the rates of ovarian and uterine cancers and slightly increase the incidence of cervical cancer.