The most common side effects of the morning-after pill are nausea, headache, fatigue, and irregular bleeding, and they typically resolve within a day or two. No serious adverse events have been reported with the dedicated emergency contraceptive pills widely available today, which sets them apart from the older estrogen-containing regimens that earned emergency contraception its reputation for rough side effects. But the experience varies depending on which type of pill you take, your body weight, and where you are in your cycle.
The Most Common Side Effects
Emergency contraceptive pills come in two main hormonal varieties: levonorgestrel (sold as Plan B and generics) and ulipristal acetate (sold as ella). Both cause a similar set of mild, short-lived side effects, though the specific rates differ slightly between them.
With levonorgestrel, roughly one in four users experiences nausea, and about one in twenty vomits. Headache, dizziness, fatigue, and breast tenderness can also show up in the first day or two but rarely linger beyond 48 hours.1PubMed Central. Emergency contraception: dispelling the myths and misperceptions A study focused on adolescent users found the same pattern of mild, expected side effects with no serious adverse events and no difference in side-effect rates by age.2PubMed. Tolerability of levonorgestrel emergency contraception in adolescents
Ulipristal acetate has a similar side-effect profile. The most commonly reported effects include headache (about 18%), nausea (about 12%), and abdominal pain (about 12%).3Pediatrics. Emergency Contraception – Section: Adverse Effects and Contraindications Because ulipristal works through a different receptor mechanism than levonorgestrel, some people assume its side effects would be noticeably different, but the evidence shows they are mild and broadly comparable.4PubMed. Update on emergency contraception
How the Older Method Compares
Before dedicated emergency contraceptive pills existed, the standard method was the Yuzpe regimen, which combined regular birth control pills containing both estrogen and progestin at high doses. This older approach was substantially harder on the stomach. Around half of women using it experienced nausea, and about one in five vomited.3Pediatrics. Emergency Contraception – Section: Adverse Effects and Contraindications A direct comparison found that the levonorgestrel-only regimen cut nausea rates roughly in half and reduced vomiting by about two-thirds relative to the Yuzpe method.1PubMed Central. Emergency contraception: dispelling the myths and misperceptions
The Yuzpe regimen is rarely used today in countries where dedicated pills are available, but it still matters for two reasons. First, it’s the fallback option in places where Plan B or ella aren’t stocked, because any combined oral contraceptive pill can technically be used at the right dose. Second, much of the lingering reputation that emergency contraception “makes you really sick” traces back to Yuzpe-era experiences. If you’ve heard horror stories from someone who took it in the 1990s, they were probably dealing with the estrogen component that modern pills don’t include.
What to Do If You Vomit
This is one of the most practical questions about emergency contraception, because vomiting can actually undermine its effectiveness. For both levonorgestrel and ulipristal acetate, the standard guidance is that if you throw up within three hours of taking the pill, you should take another dose.3Pediatrics. Emergency Contraception – Section: Adverse Effects and Contraindications The pill needs time to be absorbed, and vomiting too soon can mean the active drug didn’t get into your bloodstream in sufficient amounts.
If nausea is a concern based on past experience, taking the pill with a small amount of food is unlikely to change the nausea risk much. For the Yuzpe method, food intake didn’t appear to affect nausea or vomiting rates.3Pediatrics. Emergency Contraception – Section: Adverse Effects and Contraindications Routine use of anti-nausea medication before taking levonorgestrel isn’t recommended, since the nausea rate is already low enough that most users won’t need it. However, if you’ve had vomiting issues with emergency contraception before, speaking to a pharmacist about an over-the-counter antiemetic is reasonable.
Changes to Your Period
Irregular bleeding is one of the most common and most anxiety-inducing side effects. Emergency contraception can shift your menstrual cycle in several ways. Your next period might arrive a few days early or a few days late. You might experience spotting or light bleeding between when you take the pill and when your period is due. The bleeding pattern in the cycle you take emergency contraception is commonly altered.1PubMed Central. Emergency contraception: dispelling the myths and misperceptions
The timing depends on where you were in your cycle when you took it. If you took levonorgestrel before ovulation, your period is more likely to come early. If you took it after ovulation, it may be delayed. A period that’s more than a week late after taking emergency contraception is worth a pregnancy test, not because the pill caused a problem, but because no method is 100% effective and you want to know.
This cycle disruption is temporary. By the following cycle, things generally return to your normal pattern. The effect is a one-time hormonal nudge, not a lasting change to how your cycle works.
Body Weight and Effectiveness
This isn’t strictly a “side effect,” but it’s closely related to how people experience emergency contraception and what they can expect from it. Research has found that levonorgestrel-based pills become less effective at higher body weights. One analysis found that women with a BMI of 30 or above had roughly four times the risk of pregnancy compared with women who had a BMI under 25 after using levonorgestrel emergency contraception. At a body weight of around 80 kilograms (about 176 pounds), the pregnancy rate after taking levonorgestrel rose above 6%, which is roughly the estimated chance of pregnancy without any contraception at all. Below 75 kilograms, the pregnancy rate stayed under 2%.5PubMed Central. Safety and effectiveness data for emergency contraceptive pills among women with obesity: a systematic review
This doesn’t mean the pill is dangerous at higher weights. The side-effect profile stays the same. But it does mean the pill may not work as well, which matters for the decision about which method to choose. Ulipristal acetate appears to maintain its effectiveness somewhat better across a wider weight range, and the copper IUD is unaffected by body weight entirely. If you’re above roughly 75 kilograms and need emergency contraception, these are worth discussing with a provider.
Ectopic Pregnancy and Emergency Contraception
One concern that comes up repeatedly is whether emergency contraception increases the risk of an ectopic pregnancy, where a fertilized egg implants outside the uterus. This worry partly stems from the fact that among the small number of pregnancies that do occur after emergency contraception fails, a somewhat higher proportion are ectopic compared with pregnancies in the general population.
A systematic review found that among pregnancies of known location that occurred after levonorgestrel treatment, about 1% were ectopic.6PubMed Central. Ectopic Pregnancy and Emergency Contraceptive Pills: A Systematic Review A more recent meta-analysis found that the overall prevalence of ectopic pregnancy after levonorgestrel emergency contraception was extremely low, not statistically different from zero, but that levonorgestrel did appear to increase the relative odds of an ectopic pregnancy when pregnancy occurred.7PubMed. A systematic review and meta-analysis of the prevalence and association between levonorgestrel and ectopic pregnancy
The distinction here is important. Emergency contraception prevents the vast majority of pregnancies from happening at all. Among the very few that slip through, a slightly higher share end up ectopic. This doesn’t mean the pill “causes” ectopic pregnancy in the way that, say, smoking causes lung cancer. The most likely explanation is that levonorgestrel is better at preventing normal uterine implantation than at preventing ectopic implantation, so when it fails, the failures are skewed. In absolute terms, ectopic pregnancy after emergency contraception is rare. But if you’ve taken the pill and experience severe lower abdominal pain, shoulder-tip pain, or unusual bleeding weeks later, you should seek medical attention.
Safety During Breastfeeding
If you’re breastfeeding and need emergency contraception, levonorgestrel is generally considered safe. A systematic review covering both randomized trials and observational studies found no adverse effects of progestogen-only contraceptive methods on breastfeeding performance through 12 months postpartum. The same body of research showed no adverse effects on infant growth, health, or development from six months up to six years of age, and no measurable effects on infant immunoglobulins or sex hormones in exposed male infants.8PubMed. Progestogen-only contraceptive use among breastfeeding women: a systematic review
Ulipristal acetate is handled a bit differently. Because it works through a different mechanism and there’s less long-term data on its transfer into breast milk, the standard recommendation is to pump and discard breast milk for about 24 hours after taking ella, then resume nursing. This is a precautionary measure rather than a response to documented harm, but it’s worth knowing about in advance so you can plan.
Psychological Effects and Expectations
Some people worry that taking the morning-after pill will cause mood swings, anxiety, or depression. The evidence on this is reassuring. An older study that tracked emotional distress in 120 patients before and after taking emergency contraception found that anxiety, guilt, and depression scores were actually elevated before treatment, likely due to the stressful circumstances that led to needing it, and decreased significantly within two weeks. The treatment itself did not produce negative psychological effects despite physical side effects in some patients.9PubMed. Emotional distress in morning-after pill patients
What’s interesting is how much expectations shape the experience. Research on contraceptive pill users more broadly has found that the number of symptoms people expect to have is tied to how anxious they are, how concerned they feel about the medication, and whether they believe medications are generally overused. People with higher trait anxiety expected more symptoms.10PubMed Central. Expectations versus reality: Two cross-sectional studies on expected and experienced discontinuation symptoms in current and former contraceptive pill users This doesn’t mean side effects are imagined, but it does suggest that the dread surrounding emergency contraception can amplify the subjective experience of taking it. Going in knowing that the most likely outcome is mild, short-lived discomfort may genuinely make it easier.
Long-Term Effects and Fertility
One of the most persistent misconceptions about the morning-after pill is that repeated use damages fertility or causes lasting health problems. The available evidence does not support this. Emergency contraceptive pills deliver a single, short-acting dose of hormone. Side effects are generally mild and self-limiting, resolving within the first 48 hours.1PubMed Central. Emergency contraception: dispelling the myths and misperceptions There is no accumulation effect from using emergency contraception more than once, and no evidence that it impairs your ability to become pregnant later.
That said, emergency contraception is less effective than regular contraceptive methods used consistently. It’s designed as a backup, not a primary strategy. The side effects themselves aren’t a reason to avoid repeated use if you need it, but the reduced reliability compared with daily pills, an IUD, or an implant is.
The Copper IUD as an Alternative
The non-hormonal option for emergency contraception is the copper IUD, which can be inserted within five days of unprotected sex and is the most effective emergency method available. Because it doesn’t use hormones, it avoids the nausea, headache, and fatigue associated with the pills entirely. Its side effects are different in character: cramping during insertion, heavier periods for the first few months, and sometimes spotting between periods.
The copper IUD also has the advantage of continuing to work as ongoing contraception for up to ten years. The insertion process itself is uncomfortable, and it requires a clinic visit rather than a pharmacy trip, which limits access in time-sensitive situations. But for someone who also wants long-term contraception, or who has a body weight that reduces the effectiveness of oral options, or who has had bad experiences with hormonal side effects, the copper IUD addresses multiple concerns at once. The trade-off is convenience and upfront discomfort versus a hormone-free method that keeps working long after the emergency has passed.
When Something Isn’t a Side Effect
Not everything that happens after taking emergency contraception is caused by it. A common source of confusion is breast tenderness or bloating that shows up a week or two later, which is often a normal premenstrual symptom arriving on a slightly shifted schedule because the pill moved your cycle. Similarly, fatigue in the days after taking emergency contraception can be hard to separate from the stress and sleep disruption that often accompany the circumstances that led to taking it in the first place.
The most important thing to watch for is what does not happen: your period. If your period is more than a week late, take a pregnancy test. Emergency contraception reduces the chance of pregnancy substantially but does not eliminate it. A late period after the morning-after pill is more often a side effect of the hormonal disruption than a sign of pregnancy, but the only way to know for sure is to test. And if you experience severe abdominal pain, particularly on one side, in the weeks following emergency contraception, seek medical care promptly, as this can be a sign of ectopic pregnancy regardless of how rare it is.