Plan B won't affect your fertility, but it can cause other side effects and isn't an effective long-term form of birth control

plan b taking a pill birth ontrol — Plan B is a type of emergency contraception that can prevent an unintended pregnancy.
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Plan B does not affect your future fertility, no matter how many times you take it.
However, you should not use Plan B as a long-term form of birth control because it can cause irregular bleeding, headaches, and fatigue.
Birth control options that are more effective include the pill, patch, implants, and IUDs.
Visit Insider’s Health Reference library for more advice.

Plan B is a type of emergency contraception that delays or prevents ovulation. It can decrease your chance of getting pregnant immediately after unprotected sex, but does not affect long-term fertility and will not prevent you from becoming pregnant in the future.

Here is what you need to know about how Plan B works and why it doesn’t affect fertility.

No, plan B does not affect fertility

Plan B works by temporarily delaying or preventing ovulation, which is when the ovaries release a mature egg. Plan B affects ovulation for one cycle, but it does not impact future fertility, says Kate White, MD, an associate professor of obstetrics and gynecology at Boston University School of Medicine.

Plan B contains levonorgestrel, a type of progestin hormone also present in birth control pills, that delays or prevents the release of an egg. It may also make vaginal fluid thicker, which can prevent sperm from reaching an egg.

A 2018 very large analysis found contraceptive use, regardless of its duration, does not impact future fertility. Taking plan B multiple times will also not impact your future fertility, White says.

"The contraceptive hormone in plan B, progestin, leaves [your] system within days and doesn't affect ovulation, tubal function, the uterus, or cervix in the future," White says.

You can take Plan B as often as it is necessary

You can take plan B as often as you think necessary, but taking it more than once in the same week does not make it more effective, says Zaher Merhi, MD, founder of the Rejuvenating Fertility Center in New York City.

You can take plan B up to 72 hours after having unprotected sex, but the longer you wait the less effective it is. Because plan B primarily works by preventing or delaying ovulation, taking it more than once in the same week, even if you've had unprotected sex twice, will not make it more effective, Merhi says.

While it's safe to take plan B as often as you think necessary, it can cause some uncomfortable side effects, Merhi says. These include:

Nausea
Headache
Breast tenderness
Dizziness
Fatigue

Because plan B contains a higher dose of levonorgestrel than birth control pills, it causes a more drastic hormonal change in your body, Merhi says. This isn't harmful but it can lead to uncomfortable side effects. Other forms of birth control are more effective and cause fewer side effects than plan B while still ensuring contraception.

Plan B is not an effective long-term form of birth control

Plan B is about 75% to 89% effective in preventing pregnancy when taken within three days of unprotected sex, but it shouldn't be used as a long-term form of birth control, White says.

Although plan B can decrease your chances of becoming pregnant after unprotected sex or if your method of birth control fails, White recommends more effective, and affordable options for long-term contraception, including:

Plan B won't affect your future fertility or lead to harmful long-term health effects, but it can disrupt your period, which is another reason it isn't recommended as a long-term form of contraception, White says.

You're more likely to experience irregular bleeding during a cycle in which you've used plan B, and that irregularity may increase with multiple doses, White says. It may also delay the timing of your next period.

Insider's takeaway

You can take Plan B as often as you think necessary and it will not impact your future fertility. However, Plan B is not recommended as a form of long-term birth control because it is less effective than other forms of birth control, like the pill or an IUD. Talk with your doctor about the best form of long-term contraception for you.