Birth control pills are commonly used to regulate menstrual periods in women whose periods are irregular (coming too often or not often enough). The pill can also reduce the length of the period and the amount of bleeding and can help decrease menstrual cramps. Menstruation is hormonally regulated, but it can be thrown off by stress, too much exercise, a poor diet, or weight gain or loss. It is also important to remember that "regular" is relative – the typical cycle is 28 days but cycles ranging from 22 to 45 days are still considered normal.
The pill is very popular among high school and college girls as a treatment for both irregular periods and acne, but my colleague Victoria Maizes, M.D., notes that a request for the pill may be an indirect way of asking for protection from pregnancy and suggests that this may be the time for a candid conversation about sexuality.
Sexually active young women should know that while the pill is a very effective contraceptive when used as directed, it won't protect them against sexually transmitted diseases, including herpes, gonorrhea, chlamydia, syphilis, genital warts, and HIV. For that, they need to make sure that their partners are using condoms.
Your daughter should also be aware of the potential side-effects of the pill. These may include nausea (it helps to take the pill with a meal or with a snack at bedtime), breast tenderness, dizziness and headaches (women who have severe migraines should NOT take it). These side effects may disappear after a few months of use, but some girls also experience mood changes and gain weight (some may actually lose weight, but I wouldn't count on this effect).
The more serious risks are high blood pressure, blood clots, heart attack and stroke, but these are rare. Problems occur most often among women who smoke, particularly those over the age of 35, who are 40 times more likely to have a heart attack or stroke than nonsmokers.
Although today's pills are safer than ever, I favor non-pharmacological methods of contraception, but that's another issue. If your daughter's periods are irregular enough to be disturbing, the pill may be the best treatment available, although there's no guarantee that they will remain regular if she stops taking it. And be sure to have that talk about sex.
Andrew Weil, M.D.