Progesterone Only Hormonal Contraception

Summary

Progestin-only contraceptives, including pills, injectables, and implants, prevent pregnancy by thickening cervical mucus, suppressing ovulation, and inducing endometrial atrophy, making them ideal for women who cannot use estrogen. Pills require strict daily timing, injectables provide long-term coverage but may delay fertility return, and implants offer up to three years of highly effective protection. Common side effects include irregular bleeding, and contraindications include breast cancer, severe liver disease, and certain cardiovascular conditions.

Overview

Progestin-only contraceptives are hormonal methods that rely solely on synthetic progesterone analogues (progestins) without the addition of estrogen. They are highly effective in preventing pregnancy, offering an alternative for individuals in whom estrogen-containing contraceptives are contraindicated, such as breastfeeding women, those with hypertension, migraine with aura, or high risk of thromboembolic disease. Their contraceptive efficacy surpasses that of barrier methods when used correctly.

The primary mechanisms of action across all progestin-only modalities include:

• Thickening of cervical mucus to inhibit sperm penetration (principal mechanism).

• Suppression of ovulation to varying degrees, depending on formulation.

• Induction of endometrial atrophy, rendering the uterine lining unsuitable for implantation.

• Reduction of tubal motility, limiting gamete transport.

Progestin-Only Oral Contraceptive Pills (POPs, “Mini-Pill”)

Composition:

Contain a low dose of progestin, such as norethisterone (350 µg), levonorgestrel (30 µg), etynodiol diacetate (500 µg), or desogestrel (75 µg). No estrogen is included.

Mechanism of Action:

• Thickens cervical mucus (primary effect).

• Suppresses ovulation in 60% of cycles with levonorgestrel-containing pills and up to 97% with desogestrel.

• Causes thinning of the endometrium.

• Reduces tubal motility.

Administration:

Taken daily at the same time without interruption; a delay of more than 3 hours (12 hours for desogestrel) can reduce efficacy.

Advantages:

• Safe during lactation; does not reduce milk supply.

• Suitable for women with estrogen contraindications.

• Fertility returns immediately after cessation.

• May reduce menstrual blood loss and risk of pelvic inflammatory disease (PID).

Disadvantages and Side Effects:

• Irregular bleeding or amenorrhea.

• Headache, acne, breast tenderness, ovarian cyst formation.

• Slightly increased risk of ectopic pregnancy due to reduced tubal motility.

• User-dependent compliance.

Efficacy:

• >3-hour delay reduces efficacy.

• Perfect use failure rate: ~0.3%

• Typical use failure rate: ~9%

Contraindications:

• Current or past breast cancer.

• Severe liver disease or tumors.

• Stroke or coronary artery disease.

• Weight >70 kg may reduce efficacy in certain formulations.

Progestin-Only Injectable Contraceptives

Depot medroxyprogesterone acetate (DMPA) every 3 months

Examples: 

• Depo-Provera® – 150 mg medroxyprogesterone acetate (IM, every 12 weeks).

• Sayana Press® – 104 mg medroxyprogesterone acetate (SC, every 13 weeks).

• Noristerat® – 200 mg norethisterone enantate (IM, every 8 weeks; short-term use).

Mechanism of Action:

• Potent inhibition of ovulation.

• Thickening of cervical mucus.

• Endometrial thinning to prevent implantation.

Advantages:

• Highly effective.

• No need for daily dosing.

• Safe in breastfeeding women and in those unable to use estrogen-containing methods.

• May reduce risk of endometrial cancer.

Disadvantages and Side Effects:

• Altered bleeding patterns (including persistent or irregular bleeding).

• Weight gain (2–3 kg in the first year).

• Loss of bone mineral density with prolonged use (usually reversible; no clear fracture risk).

• Delayed return to fertility (up to 6–12 months).

• Slightly increased risk of breast cancer.

Efficacy:

• Perfect use failure rate: ~0.2–0.3%

• Typical use failure rate: ~6%

Contraindications:

• Current breast cancer or history within 5 years.

• Severe arterial disease or high vascular risk.

• Severe liver disease or tumors.

• Planned near-future pregnancy.

Progestin-Only Subdermal Implants

Example:

• Nexplanon® – 68 mg etonogestrel rod inserted into the upper arm, effective for 3 years. Contains barium for X-ray visibility.

Mechanism of Action:

• Continuous inhibition of ovulation.

• Thickening of cervical mucus.

• Endometrial atrophy.

Advantages:

• Extremely effective and long-acting (failure rate ~0.05%).

• Immediate return of fertility after removal.

• Safe for breastfeeding women and those with estrogen contraindications.

• Efficacy unaffected by body weight, although early replacement may be considered in women with high BMI.

• May reduce endometrial cancer risk.

Disadvantages and Side Effects:

• Frequent or irregular bleeding (affects ~50% of users).

• Local irritation, bruising, or pain at insertion/removal site.

• Rarely, implant bending or breakage.

• Slightly increased breast cancer risk.

Contraindications:

• Pregnancy.

• Unexplained vaginal bleeding.

• Severe liver disease or tumors.

• Current or past breast cancer.

• Stroke or transient ischemic attack during use

Effectiveness Summary (Failure Rate %)