Sexual Health
taking plan b after unprotected sex can make your period late or irregular

Can Plan B Make Your Period Late? It Might Disrupt Your Cycle

If this happens, don’t worry — but do keep tabs on when it returns to normal.

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Sex can be messy. It can mess up your sheets, your hair, your urinary tract — your heart! (Moment of silence for all those who have been ghosted.) And if you need to take an emergency contraceptive like Plan B afterward, it can even mess with your period.

Among other (mostly minor) side effects, over-the-counter contraceptive pills like Plan B can make your period late, spotty, or just plain irregular. But according to Dr. Kate White, associate professor of OB/GYN at the Boston University School of Medicine, side effects of the morning-after pill are rare and typically resolve themselves in a matter of days or weeks. “Plan B can make your cycle more irregular for a single month,” she tells Elite Daily. “After that, your cycles will return to their baseline.”

A late period might seem like NBD to some people — but if you’re trying to prevent pregnancy, it could be an added source of stress. Still, Dr. Jennifer Dhingra, NHS doctor, sexual health advocate, and youth education expert, says the impact of Plan B on your period shouldn’t discourage you from taking it when needed. For most folks, the benefits of the pill as a reliable form of pregnancy prevention far outweigh any potential side effects — especially after the June 24 Supreme Court ruling overturning the constitutionally protected right to an abortion in the U.S.

“Emergency contraception empowers people to take control over their sexual and reproductive health by helping to prevent unwanted pregnancy,” she says. “It provides an important safety net if you have forgotten [or] have not been able to use contraception, or there is a risk of contraceptive failure, e.g., broken condoms, missed pills, [or] a delay in getting the injection.”

Since Plan B is different from an abortion pill, it’s not currently impacted by the Supreme Court’s decision in Dobbs v. Jackson, meaning it’s still on the table for most people who are trying to prevent pregnancy. If you’re considering taking Plan B but are worried about what effect it will have on your period — or, you know, the rest of your body — read on for everything you should and shouldn’t expect from the morning-after pill.

Why Does Plan B Affect Your Period?

Plan B 101: It’s a pill available over-the-counter (aka without a prescription) that’s meant to prevent a sperm from fertilizing an egg within the 24 to 72 hours following unprotected sex. It works, Dr. Dhingra explains, by delaying ovulation, or the release of an egg, which often leads to changes or disruptions in your menstrual cycle that month. As a result, your cycle might start a couple of days earlier or later than usual.

“Most people will get their period within seven days of the expected time, with less than 10% of people experiencing a delay of over seven days,” she says. “Either way, this should not affect your cycle long-term, and does not affect your long-term fertility.”

If your period is delayed by more than a week, Dr. Dhingra recommends taking a pregnancy test to be sure that the pill worked. You’ll know Plan B did its job when your next normal period comes, or when you receive a negative pregnancy test result.

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What Will Plan B Do To My Period?

In the days after taking Plan B, some people experience spotting before their next period, Dr. Dhingra says. “This is usually not concerning and something to keep an eye on,” she notes. Extra heavy periods or spotting in between periods in subsequent cycles is cause to check in with a healthcare professional, she advises, “as they may want to rule out things such as sexually transmitted infections or other gynecological causes.”

Dr. Dhingra says that while it’s safe to take Plan B multiple times during a cycle as needed, regular use might make your period even harder to predict. To avoid this, Plan B should not become your primary method of contraception. She recommends speaking with your healthcare provider about finding a regular method of contraception that’s a better fit for you.

What Are The Other Side Effects Of Plan B?

Even though Plan B can disrupt or delay your period, Dr. Dhingra says it’s still safe to take the pill even for those with conditions that impact the menstrual cycle, such as PCOS or endometriosis.

In addition to cycle changes, Dr. Dhingra says around 10% of users have reported headaches, nausea, PMS-like cramps, and breast tenderness, but nothing severe or lasting more than a week or two. As with any other medication, it’s best to check in with a healthcare professional if symptoms persist or you have any other cause for concern, like a possible allergic reaction. One very important thing to keep in mind after taking Plan B? If you vomit within three hours, you will need to repeat your dose, as the pill would not yet have had time to enter your system.

For most people, taking Plan B is safe and effective, even if it does mildly impact your period. But there are a few exceptions. “If you have a health condition that requires you to take medications that are known to induce liver enzymes, it may reduce the effectiveness of Plan B,” Dr. Dhingra says. “If this is the case, you should check in with a healthcare professional to discuss the most appropriate method of emergency contraception.”

Dr. White adds that, while it’s extremely rare, some people have known allergies to Plan B, in which case it should be avoided. It’s also not intended for anyone who is already pregnant. And lastly, birth controls that rely on progestin hormones like Levonorgestrel — a synthetic form of progesterone and Plan B’s main ovulation-blocking ingredient — have been linked to breakouts of hormonal acne in some users who are particularly acne-prone. Levonorgestrel has high androgenic properties, sometimes called “male hormones.” When not balanced with estrogen hormones (found in certain other forms of birth control, which have actually been shown to improve hormonal acne), androgen hormones can lead to increased sebum production, a major source of breakouts. Basically, hormones and skin have a very touchy relationship!

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What Else Should I Know About Taking Plan B?

There are three things Dr. White says her patients often don’t understand about Plan B. The first is that it’s more effective the sooner you take it, and the efficacy greatly decreases 72 hours after unprotected sex. For the best results, take it as soon as possible after your sexual encounter.

The second is that it’s less effective for folks who are overweight or obese. In fact, for people with a BMI 26 or higher, it might not work at all, and doubling the dose doesn’t seem to be effective, she explains.

Third, “Plan B isn’t the only emergency contraceptive,” she notes. Ella is a prescription pill that’s considered as effective or more effective than Plan B, and is effective up to a BMI of around 35. “And the most effective [emergency contraceptive] is not a pill at all, it’s an IUD,” she says. “Three different IUDs can be used for [emergency contraception] … and if you don’t want to continue using the IUD as ongoing birth control, it can be removed with your next period.”

In general, Dr. White believes there’s a stigma attached to emergency contraception, as some associate it with being lazy or irresponsible. But she says this characterization is unfair. “There is no moral difference between using contraception before or after sex if you don’t want to get pregnant,” she says. “I don’t want people to ever feel shame for using Plan B or any other ‘emergency’ contraception. It’s great to do everything you can to keep from getting pregnant when you don’t want to be.”

After all, “not all people are able to access or use contraception before they have sex,” she says. “Partners don’t always agree, and sex is not always wanted. So it’s vital for all people who can become pregnant to have access to emergency contraception.”

If you choose to take Plan B, you can feel good about exercising your reproductive freedom — even if it means making some tweaks to your period tracker along the way.

Studies referenced:

Lortscher, D., Admani, S., Satur, N., & Eichenfield, L. (2016). Hormonal Contraceptives and Acne: A Retrospective Analysis of 2147 Patients. Journal of Drugs in Dermatology, 15(6), 670–674.


Dr. Kate White, associate professor of OB/GYN, Boston University School of Medicine

Dr. Jennifer Dhingra, NHS doctor, sexual health advocate, and youth education expert

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