Progestin-Only Pills and Injectable Contraceptives
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Direct answer
Progestin-only pills and injectables contain only a progestin, so they suit women who cannot take oestrogen, including breastfeeding mothers. Depot medroxyprogesterone acetate is given as 150 mg every three months, and norethisterone enanthate is given every eight weeks. The main drawbacks are irregular bleeding and, with DMPA, loss of bone mineral density.
What you must remember
- POP mechanism: Mainly thickens cervical mucus and alters the endometrium, with inconsistent ovulation suppression.
- POP timing: Taken at the same time every day, with a grace window of about three hours.
- DMPA dosing: 150 mg intramuscularly every 12 to 13 weeks, reliably suppressing ovulation.
- NET-EN dosing: 200 mg intramuscularly every eight weeks, which may affect bone density less than DMPA, although the evidence is limited.
- Bleeding pattern: Irregular spotting is common early, and amenorrhoea is common with DMPA.
- Bone density: DMPA reduces bone mineral density, which is generally reversible after stopping, so caution applies in adolescents and women at osteoporosis risk.
- Breastfeeding: POP and DMPA are usually started from about six weeks postpartum under the Indian programme.
A stepwise approach to choosing a progestin-only method
Vignettes usually describe a woman with a specific constraint, such as breastfeeding, low bone mass or the need for a long-acting method, and the steps below help choose the right option.
- Check the constraints: Note whether the woman cannot take oestrogen, is breastfeeding, is an adolescent or has low bone mass.
- Choose the duration: Daily pills need strict adherence, while DMPA gives three-monthly cover and NET-EN gives eight-weekly cover.
- Weigh the bone effect: DMPA reduces bone density, so NET-EN or another method may be preferred when bone health is a concern.
- Counsel about bleeding: Irregular bleeding and amenorrhoea are common, and women should be told this before starting.
- Plan the return to fertility: Fertility can take longer to return after DMPA than after other methods, so this matters for women planning pregnancy.
The table below compares the three common options at a glance.
| Method | Dosing | Key concern |
|---|---|---|
| Progestin-only pill | Daily at the same time | Missed pills reduce protection |
| DMPA | 150 mg every 12 to 13 weeks | Bone loss and delayed return of fertility |
| Norethisterone enanthate | 200 mg every eight weeks | Irregular bleeding and shorter interval |
Where the exam tries to catch you
Progestin-only questions often hinge on bone density, missed-pill rules or the safety of breastfeeding.
- Trap: Counting a pill taken several hours late as fully protective. Correct: A late progestin-only pill loses its reliability, so backup contraception and missed-pill advice are needed.
- Trap: Choosing DMPA for an adolescent with low bone mass without caution. Correct: DMPA reduces bone density, so caution applies, and NET-EN or another method may be preferred.
- Trap: Withholding progestin-only methods during breastfeeding. Correct: POP and DMPA are acceptable during breastfeeding and are usually started from about six weeks postpartum.
Frequently asked questions
How do progestin-only pills prevent pregnancy?
Progestin-only pills prevent pregnancy mainly by thickening cervical mucus and altering the endometrium. They inhibit ovulation inconsistently, so the daily timing of the pill matters more than in combined pills.
What is the dosing schedule of DMPA?
Depot medroxyprogesterone acetate is given as 150 mg by intramuscular injection every three months, and it reliably suppresses ovulation. An injection delayed beyond about four weeks after the due date needs pregnancy to be excluded before the next dose is given.
What is the main long-term concern with DMPA?
The main long-term concern with DMPA is loss of bone mineral density, which is generally reversible after stopping. Caution is advised in adolescents and women with osteoporosis risk factors, and norethisterone enanthate may be considered as an alternative.
Can breastfeeding women use progestin-only methods?
Breastfeeding women can use progestin-only pills and DMPA, which are usually started from about six weeks postpartum. Oestrogen-containing methods are avoided in early breastfeeding because of thrombotic risk.