**4.3 Mechanism of action**

There are three primary mechanisms of action that contribute to the efficacy of injectable DMPA in preventing pregnancy:


### **4.4 Effectiveness**

POIs containing DMPA are one of the most effective methods of contraception. Contraceptive efficacy is achieved rapidly (<24 h) and, because there is a grace period of 4 weeks, is non-user-dependent. Nevertheless, it is important that the injections are given consistently and correctly. Pregnancy protection rates reach 99% with perfect use and 96% with typical use, assuming occasional non-use and/or incorrect use for the latter [80, 87]. The risk of pregnancy is higher when a woman misses an injection. The failure rate is up to 6 pregnancies per 100 women in the first year of use [88]. Age, income, desire to prevent or delay pregnancy, and culture affect the consistent and correct usage of any method of contraception [80].

#### **4.5 Advantages**

In general, POIs are a good choice for women who want a reliable, long-lasting, reversible method of contraception without the need for daily action on their part, such as pill-taking. This type of contraceptive can be used by women of any age and parity status and is easily discontinued. Client satisfaction is high, as injections are often considered more convenient compared to other forms of contraception and follow-up injections can be easily given by a nurse. There is no need for a pelvic examination prior to the use of POIs. Furthermore, the injections do not affect breastfeeding or interfere with intercourse. Overall, POIs have a good safety profile and few specific health risks. They have minimal drug interactions.

#### *4.5.1 Non-contraceptive uses*

Since its introduction into the market in the 1960s, DMPA has been used for a variety of gynecological conditions, including endometriosis and abnormal menstrual bleeding [81]. Because it decreases menstrual blood loss by 50% at 1 year of use and by 70% after 2 years of use, DMPA improves iron deficiency anemia and amenorrhea [83]. The mechanism of action of progestin with regards to endometrial thinning and atrophy contributes to its use in the treatment of endometriosis, plus its direct effect on endometrial lesions [86]. DMPA can also be used in the treatment of abnormal uterine bleeding associated with uterine fibroids, adenomyosis, or coagulopathies [39]. In addition, it protects against endometrial cancer and symptomatic PID.

DMPA also improves cyclical menstrual symptoms, such as pain, mood changes, headaches, and breast tenderness, and decreases the incidence of benign breast disease, ovarian cysts, and ectopic pregnancy. Furthermore, women with sickle cell disease will have fewer sickle cell crises, while those with epilepsy will have fewer *grand mal* seizures [79, 81, 82].
