The most effective thing you can do after unprotected sex to prevent pregnancy is use emergency contraception, and the sooner you act, the better it works. You have up to five days depending on the method, but effectiveness drops with every hour that passes. There are three main options: over-the-counter emergency contraception pills, a prescription pill that works longer, and an IUD placed by a healthcare provider.
Methods That Don’t Work
Before covering what does work, it’s worth clearing up a common misconception. Douching after sex does not prevent pregnancy. Sperm can enter the uterus within minutes of ejaculation, long before any rinse could wash them away. Urinating after sex also has no effect on pregnancy risk, since urine exits through the urethra, a completely separate opening from the vagina. Showering, jumping, lying in a certain position: none of these do anything to stop sperm that have already been deposited.
Over-the-Counter Emergency Contraception Pills
The most accessible option is a pill containing levonorgestrel, sold under brand names like Plan B, Take Action, My Way, and several others. You can buy it at a pharmacy without a prescription, and there is no age restriction. It works by delaying ovulation so that no egg is available for sperm to fertilize. It does not end an existing pregnancy.
Levonorgestrel is most effective when taken within 72 hours (three days) of unprotected sex, though some protection extends to five days. The key point is that it works best the sooner you take it. If you can get to a pharmacy within a few hours, do it.
Weight and Effectiveness
Levonorgestrel becomes significantly less effective at higher body weights. Research shows that people with a BMI of 30 or above had roughly four times the risk of pregnancy compared to those with a BMI under 25 when using this pill. The decline is tied to absolute weight: effectiveness drops noticeably starting around 70 kg (about 154 pounds) and appears to offer essentially no protection at 80 kg (about 176 pounds) and above. The reason is straightforward. At higher body weights, the standard dose produces peak blood levels roughly 50% lower than in lighter individuals, which may not be enough to reliably block ovulation. If you weigh more than 155 pounds, the prescription option or an IUD will be more reliable.
The Prescription Pill: Ulipristal Acetate
Ulipristal acetate, sold as ella, requires a prescription but has two advantages over levonorgestrel. First, it maintains its effectiveness for a full five days (120 hours) after unprotected sex, without the steep drop-off that levonorgestrel shows after 72 hours. Second, it works better at higher body weights, though very high BMI can still reduce its effectiveness somewhat.
Getting a prescription doesn’t have to mean an in-person doctor visit. Many telehealth services can write a prescription quickly, and some pharmacies can dispense it the same day. If you’re within the five-day window and levonorgestrel isn’t a good fit for you, this is the stronger oral option.
IUDs: The Most Effective Emergency Contraception
An IUD placed within five days of unprotected sex is the most effective form of emergency contraception available. Two types can be used: the copper IUD and the hormonal IUD containing levonorgestrel.
In a study of over 600 participants, the copper IUD prevented 100% of expected pregnancies when used as emergency contraception. The hormonal IUD prevented 93% to 96% of expected pregnancies. Nearly half the participants in both groups reported multiple episodes of unprotected sex, making these results even more striking.
The obvious drawback is access. You need an appointment with a healthcare provider who can place the device, and that may not be possible on short notice everywhere. The upside is that once placed, an IUD doubles as long-term birth control for years, so it solves both the immediate concern and the ongoing one. If you can get an appointment within five days and you want highly reliable protection, this is the best option.
What to Expect After Taking EC Pills
Emergency contraception pills commonly cause nausea, fatigue, headaches, dizziness, breast tenderness, and abdominal cramping. Some people experience light spotting. These side effects are temporary and typically resolve within a day or two.
Your next period may arrive earlier or later than usual, and it may be heavier or lighter than normal. This is expected. However, if your period is more than seven days late, take a pregnancy test. A test is most reliable starting on the first day of a missed period. If you’re not sure when your period is due, wait at least 21 days after the unprotected sex before testing.
Signs That Something Needs Attention
If emergency contraception fails and pregnancy occurs, there is a small risk of ectopic pregnancy, where a fertilized egg implants outside the uterus, usually in a fallopian tube. Early signs include light vaginal bleeding and pelvic pain. Some people feel shoulder pain or pressure in the rectum. If a fallopian tube ruptures, symptoms escalate to severe abdominal pain, heavy internal bleeding, extreme lightheadedness, and fainting. Severe pelvic or abdominal pain combined with vaginal bleeding, or any episode of fainting, warrants emergency medical care.
Choosing the Right Option
Your best choice depends on three things: how many hours have passed, your body weight, and how quickly you can access each method.
- Within 72 hours, under 155 pounds: Over-the-counter levonorgestrel (Plan B or generics) is effective, affordable, and available immediately at most pharmacies.
- Within 120 hours, or over 155 pounds: Ulipristal acetate (ella) is the better pill option. You’ll need a prescription, which telehealth can often provide quickly.
- Within 120 hours, any weight: A copper or hormonal IUD is the most effective option overall, if you can get an appointment in time. It also provides ongoing contraception.
Whatever you choose, the single most important factor is speed. Every method works better the sooner you use it. If you’re reading this right now and deciding what to do, the best next step is the fastest one you can access.