■ Four types of oral contraceptives are available. The constant – dose combination pill contains steady doses of estrogen and progestin. The triphasic pill provides fluctuations of estro­gen and progestin levels throughout the menstrual cycle. The extended-cycle pill reduces menstrual cycles to four per year. The progestin-only pill consists of low-dose progestin.

■ Advantages of oral contraceptives include high effectiveness and lack of interference with sexual activity. Birth control pills are also associated with lower incidences of uterine, ovarian, and colon cancer. An additional advantage is reduc­tion of menstrual flow and cramps. The advantage of the progestin-only pill is the reduced chance of side effects from estrogen. The vaginal ring (NuvaRing), the transdermal patch (Ortho Evra), and the injectable Depo-Provera are hormone-based contraceptives that do not require remem­bering to take a pill each day.

■ Disadvantages of hormone-based contraceptives include possible side effects such as a slight increase in the likeli­hood of blood clots, an increase in migraine headaches, nausea, fluid retention, irregular bleeding, and reduced sexual interest. Disadvantages of the progestin-only pill include irregular bleeding and the possibility of additional side effects. In general, the health risks of oral contraceptives are far lower than those from pregnancy and birth.

■ Depo-Provera is an injectable contraceptive that lasts for 3 months.