I've heard it before: The pill protects against ovarian cancer. And here the news presents itself again, this time in the form of a study revealing birth control pills can protect women from this disease even decades after they stop taking it.

British researchers have found that women taking the pill for 15 years cut their chances of developing ovarian cancer by half. The risk remained low more than 30 years later, although protection did weaken over time, according to study findings that were published Friday in The Lancet.

Overall, this is good news. Not only do you get to prevent pregnancy, you get to prevent ovarian cancer at the same time (long-term protection against endometrial cancer is a bonus too). But there's a downside to this hopeful news: The pill also slightly increases the chances of breast and cervical cancer. The risk seems to disappear once a woman stops taking the oral contraceptive but still, the gamble remains for as long as the medication is used.

Why the discrepancy? "It may have something to do with the hormones in the contraceptives," says Dr. Debbie Saslow, director of breast and gynecologic cancer at the American Cancer Society. "Hormones such as estrogen can be growth-promoting in some body parts and have the opposite effect in other body parts."

So what's a girl to do? Because there is no early test for ovarian cancer -- which is often diagnosed late with a bad prognosis -- doctors say that the pill's protective effects against ovarian cancer outweigh the small increased risks of breast and cervical cancer, unless women already have a history of those cancers.

Doctors don't recommend taking the pill just for its anti-cancer properties, but they are pretty excited that this is the first medication we know of with the power to cut ovarian cancer risk.