Emergency Contraception: Options, Timing and What to Do Next

Different emergency pills have different time windows and interactions. In the UK, levonorgestrel is used within 72 hours and ulipristal acetate within 120 hours. Other countries may have different products and access rules. Earlier use is generally better.

The main emergency contraceptive pills are levonorgestrel and ulipristal acetate. Levonorgestrel products are available without a prescription in the United States, while ulipristal requires a prescription. Both are intended to be used as soon as possible after unprotected sex, and emergency contraceptive pills can be used within a five-day window; ulipristal is generally more effective than levonorgestrel later in that window.

Emergency contraceptive pills work primarily by delaying or preventing ovulation. They do not reliably prevent pregnancy after ovulation has already occurred, which is one reason waiting for a fertility app to identify whether a day was “safe” can reduce the opportunity to use EC effectively. Temporary nausea, headache, fatigue, breast tenderness, abdominal discomfort, spotting, or a change in the timing of the next period can occur.

A copper IUD can be inserted within the clinically eligible time window and is the most effective emergency contraception. It can remain in place as ongoing contraception if the person wants that method.

The copper intrauterine device is the most effective established form of emergency contraception and can also remain in place as highly effective ongoing birth control. A trained clinician inserts it into the uterus. It can generally be placed within five days of the first episode of unprotected sex; when ovulation can be estimated reliably, clinical guidance also allows placement based on how much time has passed since ovulation.

Unlike emergency contraceptive pills, the copper IUD does not depend on body weight for effectiveness. It may not be appropriate in every situation, so the clinician assesses pregnancy possibility and standard IUD eligibility. Known active cervical gonorrhea or chlamydia or purulent cervicitis can affect whether insertion should proceed, although needing STI screening does not automatically mean an eligible person must always wait for test results before placement.

Emergency pills mainly work by delaying or preventing ovulation. Ovulation cannot be predicted perfectly with an app or calendar, so do not delay professional advice while trying to calculate an exact fertile day.

Pregnancy risk is determined by the relationship between intercourse and ovulation, not simply by the calendar date of sex. Sperm can remain capable of fertilization for several days, so intercourse before ovulation can still lead to pregnancy when an egg is released later. Ovulation itself can shift from one cycle to another, even in people whose periods are usually predictable.

Cycle-tracking apps and estimates based on the last menstrual period cannot confirm exactly when ovulation occurred. For that reason, people considering emergency contraception are generally advised not to delay while trying to calculate whether they were on a fertile day. The sooner the situation is assessed, the more likely it is that all appropriate EC options remain available.

Some emergency pills may be less suitable or effective at higher body weight or with medicines that induce liver enzymes, including certain epilepsy, TB and HIV medicines or St John’s wort. A clinician or pharmacist can compare alternatives.

Body weight can influence the effectiveness of oral emergency contraception. Evidence suggests that levonorgestrel may be less effective at higher body weights, and ulipristal may also lose some effectiveness as weight increases. There is no single proven weight at which an emergency contraceptive pill suddenly stops working, so oral EC should not simply be withheld on the basis of weight. The copper IUD remains an option whose emergency contraceptive effectiveness is not reduced by body weight.

Some medicines and herbal products that strongly increase certain liver enzymes can lower levels of emergency contraceptive pills and may reduce their effectiveness. Examples include some anti-seizure medicines, rifampin-type antibiotics, certain HIV medicines, and St. John's wort. A pharmacist or clinician can review prescription medicines, over-the-counter products, and supplements and help identify an EC option that is less affected by an interaction.

The advice for starting or restarting hormonal contraception can differ depending on which emergency pill was taken. Follow the product or clinician instructions and use condoms temporarily when advised.

What happens next depends on which emergency contraceptive pill was used. After levonorgestrel EC, regular hormonal contraception can generally be started or resumed right away, with condoms or abstinence used temporarily while the ongoing method becomes effective. Emergency contraception does not protect intercourse that occurs later in the same cycle.

Ulipristal requires a different approach because starting a progestin-containing hormonal contraceptive too soon can interfere with its action. Current guidance recommends waiting five days after ulipristal before starting or resuming hormonal contraception, followed by temporary barrier protection or abstinence while the regular method becomes effective. Nonhormonal contraception is not subject to the same interaction.

Emergency contraception can shift the next bleed. Follow the service’s pregnancy-test timing advice and seek assessment for a significantly late period, unusual bleeding or pregnancy symptoms.

The next period may arrive earlier or later than expected after emergency contraceptive pills, and spotting can occur in between. A shifted period by itself therefore does not show whether the method worked. Pregnancy testing is appropriate if a period is substantially later than expected or if there has been no menstrual or withdrawal bleeding within about three weeks after emergency contraception.

A positive pregnancy test after EC means the method did not prevent that pregnancy; it does not mean emergency contraception caused the pregnancy or harmed it. Because home tests can be negative when taken too early, repeating a test or seeking clinical testing may be appropriate when the timing remains uncertain and menstruation has not occurred.