Researchers from a U.N. cancer agency are calling combined estrogen-progestin birth control pills and menopausal hormone replacement "carcinogenic to humans."

However, they don't dismiss either type of drug. For instance, they state that birth control pills may "slightly" raise the risk of some cancers while lowering risks of other cancers.

Women should weigh the drugs' risks and benefits with their doctors, write the researchers.

The report appears in The Lancet Oncology. The researchers included Vincent Cogliano, PhD, of the World Health Organization's International Agency for Research on Cancer (IARC).

They didn't do any new studies. Instead, they reviewed past research on the topic.

The risks are not new and are already noted on drug labels, says Candace Steele, director of global public relations for Wyeth Pharmaceuticals, which makes birth control pills and menopausal hormone therapy drugs.

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Review of Birth Control Pill Studies

The researchers write that combined estrogen-progestin birth control pills may "slightly" raise breast cancer risk in women currently or recently taking those pills. But the risk seems to drop back to normal 10 years after stopping the pill, write the researchers.

The researchers note higher risks of cervical and liver cancers with combined birth control pills.

However, uterine and ovarian cancer risk is lower in women using birth control pills, they write.

Despite the slightly higher risk of some cancers, the overall risk of cancer from the pill is still low.

The IARC's assessment of cancer risk from birth control pills hasn't changed but now includes more types of cancer, write the researchers.

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Net Benefit?

Because use of the pill (forms containing both estrogen and progestin) heightens risk of some cancers and reduces that of others, it is possible that there may be an overall net benefit to public health, write the researchers. More rigorous analysis is needed to show this, they add.

The researchers cite studies showing higher breast cancer risks for women using combined hormone therapy -- containing both estrogen and progestin. They note other studies showing that uterine cancer risk is higher in women taking estrogen-only therapy, compared to those taking estrogen and progestin.

When progestin is taken every day, the risk is much the same as that in women who have never used hormonal treatment, they write.

"There are both beneficial and adverse effects for oral contraceptives and menopausal therapy," states an IARC news release. Each woman who uses these products should discuss the overall risks and benefits with her doctor.

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Drug Company: Nothing New Here

The IARC's change regarding combined hormone therapy "is based on data published since 1999," Steele tells WebMD.

"Estrogen and progestin data from those studies have previously been published in medical literature and have been incorporated into the product labeling for estrogen and progestin therapies," she says.

"I think it's important to note that the information in the IARC's most recent guidelines is consistent with the current clinical practice and all class labeling for our company's estrogen and estrogen-plus-progestin therapies, as well as for our oral contraceptive products," says Steele.

"The IARC last made their report in 1999, so they're just updating [it] based on new information since then. We, of course, have been updating our label all along. So the information that's included in that report is already included in our label," says Steele.

Millions of women use oral contraceptives or hormone therapies, notes Steele. "I really feel that the best source of information is a woman's physician, and that this information should be taken in context with a risk and benefit assessment made with her physician," she says.

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By Miranda Hitti, reviewed by Michael W. Smith, MD

SOURCES: Cogliano, V. The Lancet Oncology; August 2005; vol 6: pp 552-553. Candace Steele, director, global public relations, Wyeth Pharmaceuticals. News release, IARC. Associated Press.