The most common side effects of the morning-after pill are nausea, headache, and changes to your next period. These effects are temporary, typically resolving within a day or two, and the pill has no impact on your future fertility. There are two types of morning-after pill available, and their side effect profiles differ slightly.
The Most Common Side Effects
Both types of morning-after pill share a core set of side effects. Nausea is the one most people notice first, sometimes hitting within a couple of hours. Headache is equally common. Beyond those two, you may experience fatigue, dizziness, breast tenderness, or lower abdominal cramping. Some people also have light spotting or bleeding between periods.
The prescription version (sold as ella) has more precise data from clinical trials. In those studies, 18% of women reported headache, 12% reported nausea, and 12% reported abdominal pain. Fatigue and dizziness each affected about 5 to 6% of users. Period-like cramping occurred in 7 to 13% of women. These numbers give a reasonable picture of what to expect from either type, since both work through similar hormonal mechanisms.
Most of these side effects fade within 24 to 48 hours. If nausea is severe, an over-the-counter anti-nausea medication can help. One practical concern: if you vomit within two hours of taking the pill, it may not have been fully absorbed. In that case, you likely need another dose. A pharmacist can confirm whether a repeat dose is necessary.
How Your Next Period May Change
The most noticeable aftereffect for many people isn’t nausea or headache. It’s a shift in when their next period arrives. The morning-after pill can push your period earlier or later than expected, sometimes by up to a week. With the prescription version specifically, 7% of women in clinical trials got their period more than seven days early, while 19% experienced a delay of more than seven days. On average, cycles lengthened by about 2.5 days.
About 9% of ella users also experienced spotting or bleeding between periods. These cycle changes are a one-time disruption. Your period typically returns to its normal pattern in the following cycle. If your period is more than a week late, though, take a pregnancy test. A late period doesn’t necessarily mean the pill failed, but it’s worth confirming.
Differences Between the Two Pill Types
The over-the-counter version (Plan B and its generics) contains a synthetic form of progesterone. The prescription version (ella) uses a different compound that blocks progesterone receptors. Both can cause the same general side effects, but there are a few distinctions worth knowing.
Ella tends to cause more pronounced period changes, including the longer delays mentioned above. Some users have also reported acne after taking it, something not typically seen with the over-the-counter version. On the other hand, the over-the-counter version is sometimes associated with heavier or more painful periods in the cycle following use.
One important practical difference: body weight can affect how well each pill works. Both types may be less effective for people with a BMI of 30 or above. The CDC notes that people in this weight range experience a higher risk of pregnancy after using either pill compared to those with a BMI under 25. The pills are still safe to take regardless of weight, but if efficacy is a concern, a copper IUD placed within five days is the most reliable emergency contraception option at any body size.
Symptoms That Need Attention
The vast majority of side effects are mild and short-lived. A few symptoms, however, warrant a call to your doctor:
- Severe abdominal pain. This could be a sign of an ectopic pregnancy (a pregnancy outside the uterus), which is a medical emergency regardless of whether you’ve taken emergency contraception.
- Very heavy bleeding. If you’re soaking through a pad every hour for two hours or more, that level of bleeding needs medical evaluation.
- Persistent vomiting. If you can’t keep the pill down, a doctor can prescribe anti-nausea medication and help you figure out next steps.
These situations are uncommon. They’re listed not to alarm you but so you can recognize them if they happen.
No Effect on Future Fertility
One of the most common concerns people have is whether taking the morning-after pill, especially more than once, could affect their ability to get pregnant later. It does not. The hormonal changes the pill triggers are short-lived, and there is no evidence that single or repeated use causes any lasting impact on fertility. Your normal ovulation pattern resumes in the next cycle.
That said, the morning-after pill is designed as a backup, not a routine method. It’s less effective than regular contraception, and the side effects, while minor, are unpleasant enough that most people prefer not to repeat the experience frequently. If you find yourself reaching for emergency contraception often, a longer-term method will give you better protection with fewer disruptions to how you feel day to day.