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Birth control pills are a popular and effective method of contraception. However, some factors, such as missing pill days, vomiting, and taking certain medications, can reduce the effectiveness of the pill and may result in unintended pregnancies.
How effective is the pill?
The combined pill contains hormones that prevent ovulation, which is when the ovaries release an egg for fertilization. Another type of pill, known as the minipill, causes a person’s cervical mucus to thicken and the uterine lining to thin, which reduces the likelihood of sperm reaching an egg.
The birth control pill is very effective if a person takes it correctly and does not miss any pill days. According to the Centers for Disease Control and Prevention (CDC)Trusted Source, the pill is 99.7% effective with perfect use. This means that less than 1 out of 100 women who take the pill would become pregnant in 1 year.
However, with typical use, the effectiveness of the pill is 91%. This means that around 9 out of 100 women would become pregnant in a year of taking the pill.
Five reasons for pill failure
Although the birth control pill is generally very effective, some situations can reduce its effectiveness and may sometimes result in unintended pregnancies. These include:
Missing a day
Manufacturers intend for people to take the pill daily for it to be most effective. If a person misses a day, their hormone levels may not remain at consistent enough levels to prevent pregnancy.
If a person finds it difficult to take the pill on a daily basis, other birth control methods may better suit their needs. A doctor or gynaecologist can advise on the range of alternative contraceptives.
Vomiting
Sometimes a person may be ill when they take the pill. When a person vomits, the pill can come back up, or they may not fully absorb it into their body.
Anyone who experiences vomiting shortly after taking the pill should take another pill as soon as possible and then take their next pill as usual.
Not taking the pills at the same time each day.
In addition to taking birth control pills daily, a person should also take the pills at around the same time each day. This can maintain their hormone levels more consistently.
A person should always take the mini pill within the same 3-hour time window every day. Someone who misses their window should use a backup birth control method for the next 2 days or avoid having sex.
Many people set a daily alarm reminding them to take their pill at the correct time each day.
Not starting a new pack right away
It is essential to start a new pack of pills the day after finishing the previous one. However, sometimes a person may not have their new package yet. Missing a few days between packs can make the pill less effective at preventing pregnancy.
According to the CDCTrusted Source, anyone who misses two or more pills in a row should use a backup contraceptive method or avoid sexual intercourse until they have taken the birth control pill for 7 consecutive days.
Medications that interfere with the pill
Some medications can make the pill less effective. Medications include certain antibiotics, such as rifampicin, and anti-fungal drugs, such as griseofulvin.
A person should use backup contraception while taking these medications and for 48 hours after finishing the course.
Other more long-term medications and supplements may also affect how well birth control pills work. These can include:
- epilepsy drugs, such as phenobarbital, phenytoin, and carbamazepine
- anti-viral medications used to treat HIV
