Combination pills contain estrogen and progestin, a synthetic form of the hormone progesterone, whereas progestin-only pills only contain progestin. Progestin-only pills (also known as the minipill) have a lower progestin content than combination pills. Because the minipill doesn’t contain estrogen, it isn’t quite as effective at preventing pregnancy, and it’s a little harder to use. However, because it doesn’t contain estrogen, it doesn’t come with any estrogen-related side effects.
The minipill is typically recommended to breastfeeding women, as, a) combination pills were long thought to harm lactation (though this has since been proven false), and b) the minipill can actually improve milk production. The minipill is also recommended to women with estrogen-sensitive health problems, such as high blood pressure, a history of blood clots, or extreme migraines. The minipill might be a good choice for you if you’ve experienced heavy side effects on a combination pill.
Because the minipill only possesses enough progestin to regulate the uterus for 24-hours, it must be taken every day within the same three-hour time window (unlike the combination pill, which allows for more wiggle room in dosage timing). The minipill starts protecting you from pregnancy 48 hours after it’s ingested, no matter where you are in your cycle. When accounting for human error, it’s about 87% effective, as opposed to the combination pill’s 91% effectiveness. The minipill also differs from the combination pill in its effect on your period. Every pill in the 28-day minipill pack is active, even the last week. Only 50% of women on the minipill ovulate regularly, so the minipill is not as effective as the combination pill at regulating your period. You may also find you miss your period entirely on the minipill, which is a normal side effect.
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