Benefits
Unlike oral contraceptive pills which have to be taken at roughly the same time each day (Combined Oral Contraceptive Pill within 12 hours and Progesterone only pill within 3 hours), the effectiveness of Depo Provera is not dependent upon the ability to remember to take daily doses. The only continuing action is to book subsequent follow-up injections every twelve weeks.

Likewise, Depo Provera is not affected by absorption issues (diarrhea, vomiting, bowel disorders) nor by antibiotic effects on the normal gut bacterial flora.

It provides hormonal birth control without the risks associated with estrogen and may in fact reduce the risk of ovarian and endometrial cancers.

Depo Provera, like progestin-only pills, may be used by breast-feeding mothers; this is not the case for combined oral contraceptive pill. Heavy bleeding is possible if given in the immediate postpartum time and is best delayed until six weeks after birth. It may be used within five days if not breast feeding.

Disadvantages & side effects

Recent research has shown that Depo-Provera significantly decreases bone density in women, as compared with others in the same age group . For some women, Depo-Provera may have a number of potentially intolerable side effects, including loss of interest in sexual activity, infertility, severe headaches, constant bleeding (metrorrhagia), weight gain, panic attacks, muscle pain, heart palpitations, pain during sex, and acne. Side effects of Depo-Provera may persist up to 24 months after the last injection.

Those planning a pregnancy after having used Depo-Provera may wish to switch to alternative contraceptive methods some 6-9 months prior. Whilst it only gives consistent contraception for 12 weeks, and pregnancy is possible after 13 weeks if not repeated in time, fertility may be temporarily reduced in some women for up to 24 months with average fertility returning in approximately 9 months.

Depo-Provera is also used with male sex offenders as a form of chemical castration as it has the effect of drastically reducing sex drive in males.

A study of 819 women in one city found an association between using Depo-Provera and higher incidence of chlamydia and gonorrhea.

One side effect (which some consider a benefit) is that many women stop having a regular menstrual cycle while on the drug. One reason for people not choosing this method of contraception is hypodermic needle phobia.

Black box warning
While it has long been known that Depo-Provera causes bone loss, it has recently been discovered that the osteoporotic effects of the injection grow worse the longer Depo-Provera is administered and may last long after the injections are stopped. For this reason, on November 17, 2004 the United States Food and Drug Administration and Pfizer agreed to put a "black box warning" on Depo-Provera's label. However the most recent evidence reviewed by WHO (World Health Organization) has weighed the benefits and risks assoiated with DMPA use and have given it a green signal for long term use. Cohort studies have shown that BMD loss is reversible within 30 months of discontinuation of DMPA and that in adolescents the recovery is much quicker.