Birth control methods that can be injected may contain two hormones, a progestin and an estrogen. These combined injectable contraceptives (CICs) are effective in preventing pregnancy and can be stopped when a woman wants to get pregnant. This review looked at CICs for how well they prevented pregnancy and for the bleeding patterns and other side effects that may occur. We also studied whether women stopped using them early and whether women liked them.
We did computer searches to find randomized trials of CICs. We included studies that compared a CIC with another birth control method. The other method could be another injectable contraceptive, either combined or having only a progestin. The CIC could also be compared to another hormonal method (like the pill) or to condoms, the diaphragm, or a placebo (or 'dummy').
We found 12 trials that studied 4 types of CICs. The combined methods required monthly injections. Four trials compared a CIC to 'depo', which has only a progestin. 'Depo' injections should be taken every three months. Five trials compared a CIC with a different combined injectable. Three trials compared a combined injectable with a different dose of the same hormones, with a progestin-only injectable, or with an intrauterine device (IUD).
More women using combined injectables had normal bleeding than women using progestin-only injectables like 'depo.' Also, fewer women using CICs stopped using them because of bleeding reasons than progestin-only users. However, users of combined injectables were more likely to stop using them overall and to stop for other medical reasons. Many factors can affect whether women keep using the method, including whether the women liked it.