Information from the Nurses' Health Study indicated that the combination of estrogen and androgen used to treat hypoandrogenism could increase breast cancer risk. However, other studies indicated androgens may decrease breast cancer risk. Follow-up studies on the Women's Health Initiative found women who received estrogen and no progestogen showed a significant decrease in cardiovascular disease (CVD) and breast cancer. This has caused a reconsideration of androgens added to estrogens. Still, the FDA requires demonstration of CVD and breast cancer safety for any product containing androgens or estrogen plus an androgen; that has not been done.
Most oral contraceptives (birth control pills) combine estrogen and progestin (natural or synthetic progesterone), but some contain only progestin. Examples of progestin-only contraceptives include the Norplant implant and the Depo-Provera contraceptive device. Progestin aids in preventing ovulation, alters the lining of the uterus, and thickens cervical mucus -- processes that help to prevent conception and implantation. The estrogen in birth control pills prevents egg production. Oral contraceptives have many side effects, so their use should be discussed with a physician.