From the Guidelines
The progesterone-only pill (POP) has a time window of only 3 hours for effectiveness, and if taken more than 3 hours late, a missed pill should be taken immediately and backup contraception used for the next 2 days. This strict timing is necessary because POPs work primarily by thickening cervical mucus to prevent sperm entry and sometimes by preventing ovulation, effects that diminish more quickly than with combined pills 1. The POP is taken continuously without breaks, meaning one pill is taken every day of the month with no hormone-free interval.
Key Considerations
- If a pill is missed and it has been more than 3 hours since the usual time, the missed pill should be taken as soon as possible, and the next pill should be taken at the usual time, which may mean taking two pills in one day 1.
- Backup contraception, such as condoms, should be used for 2 consecutive days after a missed pill to ensure protection against pregnancy 1.
- Newer progestin formulations like desogestrel (Cerazette) may offer a slightly longer window of 12 hours, but traditional POPs like Micronor, Noriday, or Nora-BE have a 3-hour window 1.
Clinical Implications
- The importance of taking the POP at the same time every day cannot be overstated, as missing a pill or taking it late can significantly reduce its effectiveness.
- Patients who frequently struggle with taking pills at the same time daily may want to discuss longer-acting progesterone methods with their healthcare provider, such as the implant or hormonal IUD, which don't require daily attention.
- Healthcare providers should emphasize the need for strict adherence to the dosing schedule and provide guidance on what to do in case of a missed pill to minimize the risk of unintended pregnancy.
From the Research
Progesterone Only Pill Window
- The progesterone only pill (POP) has a recommended "three-hour window" of tolerance before back-up contraception should be used if a pill is taken late 2.
- However, studies have found that different progestins have different properties that determine the effect of delayed or missed pills on effectiveness at preventing pregnancy, suggesting that there may be more margin for error for some POPs than guidelines suggest 2.
- A review of randomized controlled trials of progestin-only pills found that evidence is insufficient to compare progestin-only pills to each other or to combined oral contraceptives in terms of efficacy, acceptability, and continuation rates 3.
- The review also found that different progestin-only pills have different effects on bleeding patterns and pregnancy rates, but the evidence is limited by the small number of studies and the variability in study designs and outcomes 3.
- The "three-hour window" recommendation for POPs should be re-evaluated in light of these findings, as it may not be applicable to all types of progestin-only pills 2.