Examples of Progestin-Only Pills
Progestin-only pills (POPs) available in the United States include norethindrone-containing formulations (traditional POPs) and drospirenone-containing formulations (newer generation POPs). 1
Traditional First-Generation POPs
- Norethindrone is the most common first-generation progestin used in traditional POPs, which require strict timing and must be taken at the same time each day 1, 2
- Traditional norethindrone POPs must be taken within a 3-hour window; if taken more than 3 hours late, backup contraception should be used for 48 hours 1
- These formulations work primarily by thickening cervical mucus rather than consistently inhibiting ovulation 3
Fourth-Generation POPs
- Drospirenone 4 mg is a newer fourth-generation progestin-only pill that has antiandrogenic and anti-mineralocorticoid properties 1, 4
- Drospirenone POPs have a significantly longer window for missed pills compared to norethindrone formulations due to the longer half-life (30-34 hours) of drospirenone 1, 4
- The drospirenone formulation uses a 24-day active pill regimen followed by a 4-day hormone-free interval, which improves bleeding control compared to traditional POPs 4
- Studies have demonstrated that ovulation inhibition is maintained even if a single drospirenone pill is missed for 24 hours 4
Other Progestin-Only Formulations (Not Available in US)
- Desogestrel 75 mcg is available in some countries outside the United States and provides more consistent ovulation inhibition than traditional POPs, with a Pearl index of 0.14-0.41 5
- Levonorgestrel 30 mcg is another formulation used internationally as a progestin-only pill 5
Clinical Considerations
- All POPs are associated with irregular bleeding patterns as a common side effect, which is the most frequently cited reason for discontinuation in up to 25% of users 6
- POPs do not protect against sexually transmitted infections; condoms must be used concurrently for STI protection 1, 2
- POPs are particularly suitable for women with contraindications to estrogen, including those who are breastfeeding, have cardiovascular risk factors, hypertension, history of venous thromboembolism, or migraine with aura 1, 2