Birth control pills are highly effective at preventing pregnancy. When taken exactly as directed, the effectiveness is about 99% , meaning fewer than 1 in 100 women will become pregnant in a year of perfect use. However, with typical use, which accounts for missed pills or other user errors, effectiveness drops to around 91-93% , meaning about 7 to 9 out of 100 women may become pregnant annually while using the pill typically.
How Effectiveness is Measured
- Perfect use means taking the pill at the same time every day without missing any doses.
- Typical use accounts for human errors such as forgetting to take the pill, vomiting shortly after taking it, or taking certain medications that interfere with absorption.
How Birth Control Pills Work
- They prevent ovulation (the release of an egg).
- They thicken cervical mucus to block sperm from entering the uterus.
- They thin the lining of the uterus to reduce the chance of implantation.
Factors That Affect Effectiveness
- Missing pills or taking them late (more than 24 hours late) can reduce effectiveness.
- Vomiting or severe diarrhea soon after taking the pill.
- Interactions with certain medications or herbal supplements.
Additional Benefits and Risks
- Can improve acne, regulate periods, and reduce menstrual pain.
- Risks of serious side effects like blood clots are very small but slightly increased compared to non-users.
- Fertility returns quickly after stopping the pill.
In summary, birth control pills are very effective when used correctly but slightly less so with typical use due to missed doses or other factors.
