PIP: In this article, Dr. Andrew M. Kaunitz, associate professor of obstetrics and gynecology at the University of Florida Health Sciences Center in Jacksonville, gives suggestions for prescribing Depo-Provera. While Depo-Provera works as a contraceptive primarily by inhibiting ovulation, it has other antifertility effects, such as endometrial atrophy and cervical mucus thickening, which help prevent pregnancy in case ovulation does occur. A usual dose of Depo-Provera, 150 mg given intramuscularly every 3 months, has a contraceptive efficacy rate of 99.6%--the highest rate for any hormonal method. Kaunitz explains that the initial injection of the drug should take place within 7 days of the beginning of menses to ensure that there is no pregnancy. Efficacy is highest up to 12 weeks after injection, even though ovulation does not take place 14 weeks after the drug is administered. In the event that the patient is more than 2 weeks late in receiving her second or subsequent injection, Kaunitz recommends obtaining a pregnancy test. Because of possible adverse effects on carbohydrate metabolism and lipoprotein levels, Kaunitz suggests that women at high risk of cardiovascular disease or diabetes receive a lower dose of the drug, 100 mg. Similarly, very small women (those weighing under 100 lbs) may also require a smaller dose. Even at a lower dose, says Kaunitz, Depo-Provera remains highly effective, with a failure rate of 1%. Kaunitz also emphasizes prescribing Depo-Provera only to women who want a long-term contraceptive (at least 2 years), since although it does not affect fertility permanently, it does take longer for fertility to return than with oral contraceptives or Norplant.