The major difference between monthly injectables and the progestin-only injectables DMPA or NET-EN is that the monthly injectables contain an estrogen as well as these progestins, making them a combined method. Also, monthly injectables contain less progestin. These differences result in more regular bleeding and fewer bleeding disturbances than with progestin-only injectables. Monthly injectables require a monthly injection, whereas NET-EN is injected every 2 months and DMPA, every 3 months. (See the job aid Comparing Injectables.)
Largely, yes. Monthly injectables (also called combined injectable contraceptives) are similar to combined oral contraceptives (COCs). There are few long-term studies done on monthly injectables, but researchers assume that most of the findings about COCs also apply to monthly injectables. Monthly injectables, however, do not pass through the liver first because they are not taken by mouth like COCs. Short-term studies have shown that monthly injectables have less effect than COCs on blood pressure, blood clotting, the breakdown of fatty substances (lipid metabolism), and liver function. Long-term studies of the health risks and benefits of monthly injectables are under way.
No. Good evidence from studies on other hormonal methods shows that hormonal contraception will not cause birth defects and will not otherwise harm the fetus if a woman becomes pregnant while using monthly injectables or accidentally starts injectables when she is already pregnant.
No. Research on combined contraceptives finds that they do not disrupt an existing pregnancy. They should not be used to try to cause an abortion. They will not do so.
No. Some providers think that the next injection should be given only when the next monthly bleeding begins. Bleeding episodes should not guide the injection schedule, however. A woman should receive the injection every 4 weeks. The timing of injections should not be based on her monthly bleeding.
No. A woman may experience some vaginal bleeding (a “withdrawal bleed”) as a result of an injection, but there is no evidence that giving a woman who has irregular bleeding a single injection of a monthly injectable will cause her monthly bleeding to begin properly about one month later. Also, giving a pregnant woman an injection will not cause an abortion.
Women younger than age 35 who smoke any number of cigarettes and women 35 and older who smoke fewer than 15 cigarettes a day can safely use monthly injectables. (In contrast, women 35 and older who smoke any number of cigarettes should not use combined oral contraceptives.) Women 35 and older who smoke more than 15 cigarettes a day should choose a method without estrogen such as progestin-only injectables, if available. All women who smoke should be urged to stop smoking.
Generally, no. Some women using monthly injectables report these complaints. The great majority of injectables users do not report any such changes, however, and some report that both mood and sex drive improve. It is difficult to tell whether such changes are due to monthly injectables or to other reasons. There is no evidence that monthly injectables affect women’s sexual behavior.
Yes. Monthly injectables are safe for women with varicose veins. Varicose veins are enlarged blood vessels close to the surface of the skin. They are not dangerous. They are not blood clots, nor are these veins the deep veins in the legs where a blood clot can be dangerous (deep vein thrombosis). A woman who has or has had deep vein thrombosis should not use monthly injectables.
No. There may be a delay in regaining fertility after stopping monthly injectables, but in time the woman will be able to become pregnant as before, although fertility decreases as women get older. The bleeding pattern a woman had before she used monthly injectables generally returns a few months after the last injection.
Women who stop using monthly injectables wait about one month longer on average to become pregnant than women who have used other methods. This means they become pregnant on average 5 months after their last injection. These are averages. A woman should not be worried if she has not become pregnant even as much as 12 months after stopping use. After stopping monthly injectables, a woman may ovulate before her monthly bleeding returns—and thus can become pregnant. If she wants to continue avoiding pregnancy, she should start another method before monthly bleeding returns.