Common Progestin-Only Contraceptive Pills
Norethindrone (0.35 mg) is the most common progestin-only contraceptive pill available in the United States, marketed under brand names like Micronor, Nor-QD, and Camila. This progestin-only pill (POP), also known as the "mini-pill," is an effective contraceptive option for women who cannot or should not use estrogen-containing contraceptives 1.
Mechanism of Action and Effectiveness
Progestin-only pills work primarily by:
- Thickening cervical mucus to prevent sperm penetration
- Not primarily by inhibiting ovulation (unlike combined hormonal contraceptives) 1
The effectiveness of POPs:
- Typical use failure rate: 7-9%
- Perfect use failure rate is lower, but requires very stringent adherence 1
- Must be taken at the same time every day for maximum effectiveness
Indications for Use
POPs are particularly suitable for:
- Women who cannot use estrogen-containing contraceptives
- Breastfeeding women (Category 1 - no restrictions) 1
- Women with cardiovascular risk factors like hypertension 2
- Women in the immediate postpartum period (can be started immediately) 1
- Women with medical conditions that contraindicate estrogen use
Administration Guidelines
- Must be taken at the same time every day (within a 3-hour window)
- No pill-free interval (continuous use)
- If a pill is taken more than 3 hours late, backup contraception should be used for 48 hours
- New packs should be started immediately after finishing the previous pack
Side Effects and Considerations
Common side effects include:
- Irregular menstrual bleeding patterns
- Spotting between periods
- Amenorrhea in some users
Important considerations:
- POPs have a more limited margin of error than combined pills
- Effectiveness may be reduced by certain medications, particularly rifampicin and rifabutin (Category 3) 1
- Depot medroxyprogesterone acetate (DMPA) injections may be preferred for women on these medications as effectiveness is not decreased (Category 1) 1
Advantages of Progestin-Only Pills
- Safe for women with contraindications to estrogen
- Can be used immediately postpartum, even in breastfeeding women 1
- No increased risk of venous thromboembolism
- No significant effect on blood pressure 2
- May be suitable for women with certain medical conditions where combined pills are contraindicated
Other Available Progestin-Only Contraceptives
While not pills, other progestin-only contraceptive options include:
- Depot medroxyprogesterone acetate (DMPA) injections (Depo-Provera)
- Etonogestrel implant (Nexplanon/Implanon)
- Levonorgestrel intrauterine system (Mirena) 3
Clinical Pearls
- Always confirm the patient is not pregnant before initiating POPs
- Counsel patients on the importance of taking the pill at the same time every day
- Advise on backup methods if a pill is missed or significantly delayed
- Inform patients that irregular bleeding patterns are common and usually not harmful
- Consider drug interactions that may reduce effectiveness, particularly antibiotics like rifampicin 1
For women who cannot remember to take a pill at the same time daily, consider recommending longer-acting progestin-only methods like DMPA injections, implants, or IUDs, which have higher effectiveness rates with typical use 3.