The most effective step you can take to avoid pregnancy after unprotected sex is using emergency contraception as soon as possible. You have several options, and timing matters more than anything else. The sooner you act, the better each method works.
Emergency Contraceptive Pills
There are two types of emergency contraceptive pills, and they differ in how long they remain effective, how you get them, and how well they work depending on your body weight.
Levonorgestrel (Plan B and Generics)
Levonorgestrel pills are available over the counter at most pharmacies without a prescription or age restriction. You take a single pill as soon as possible within 72 hours (3 days) of unprotected sex. The sooner you take it, the more effective it is. These pills work by delaying or preventing your ovary from releasing an egg. If ovulation has already happened, the pill is far less likely to work.
Body weight significantly affects how well levonorgestrel works. Research shows the pill begins losing effectiveness at around 70 kg (about 155 pounds) and may have essentially no effect at 80 kg (about 176 pounds) or above. In people with a BMI of 30 or higher, peak drug levels in the blood are roughly 50% lower than in people with a BMI under 25, which likely explains the higher failure rates. If you weigh more than 155 pounds, the other options below are better choices.
Ulipristal Acetate (Ella)
Ulipristal acetate is a prescription emergency contraceptive pill that works within 120 hours (5 days) of unprotected sex. It requires a visit to a clinic, a telehealth appointment, or a pharmacist in states that allow pharmacist prescribing. Within the first 3 days, it performs similarly to levonorgestrel. The real advantage shows up between days 3 and 5, when ulipristal remains significantly more effective.
Like levonorgestrel, ulipristal works by blocking or delaying ovulation. It does maintain better effectiveness at higher body weights than levonorgestrel, though there are still concerns about reduced efficacy at a BMI of 30 or above. If you’re past the 72-hour window or weigh more than 155 pounds, ulipristal is the stronger pill option.
The IUD Option
Getting an IUD inserted within 5 days of unprotected sex is the most effective form of emergency contraception available. The copper IUD has been used this way for decades, and in studies, the pregnancy rate is essentially zero. A large NIH-funded study found the hormonal IUD (levonorgestrel IUD) also works as emergency contraception, with a pregnancy rate of just 0.3%.
An IUD requires a clinic visit and insertion by a healthcare provider, so it’s not as immediately accessible as a pill. But it has two major advantages: it works regardless of your body weight, and once it’s in place, it provides ongoing contraception for years. If you were already considering long-term birth control, this approach solves both problems at once.
What Doesn’t Work
Douching after sex does not prevent pregnancy. The Office on Women’s Health states this clearly: douching should never be used for birth control. Sperm reach the cervix within minutes of ejaculation, long before douching could have any effect. Worse, douching disrupts the normal bacteria in your vagina and increases your risk of sexually transmitted infections.
Other home remedies you may find online, such as drinking certain teas, using vinegar, or urinating after sex, also do not prevent pregnancy. Urinating clears the urethra, which is a completely separate opening from the vagina, so it has no effect on sperm. The only proven methods are the emergency contraceptive pills and IUDs described above.
Timing Is the Biggest Factor
Every hour matters. The FDA emphasizes that the single most important factor in how well emergency contraception works is how quickly you take it after unprotected sex. Don’t wait to see if you “feel” pregnant or try to calculate whether you were ovulating. Take it now and let the medication do its job. If a pharmacy near you is closed, many pharmacies have 24-hour locations, and some telehealth services can prescribe ulipristal with same-day pharmacy pickup.
For levonorgestrel, effectiveness drops steadily over 72 hours. For ulipristal, you have up to 120 hours, but sooner is still better. For an IUD, you have up to 5 days, but scheduling the appointment as early as possible gives you the best chance.
What to Expect Afterward
Emergency contraceptive pills commonly cause nausea, headache, fatigue, and some irregular bleeding or spotting. Your next period may come earlier or later than expected, which is normal and happens because the medication disrupted your usual hormonal cycle. These side effects are temporary and typically resolve within a few days.
You can take a pregnancy test 3 weeks after using emergency contraception to confirm it worked. Testing earlier than that can give unreliable results because pregnancy hormones need time to build up to detectable levels. If your period is more than a week late, that’s a reasonable prompt to test.
Choosing the Right Option for You
- Within 72 hours, under 155 pounds: Levonorgestrel (Plan B) from any pharmacy, no prescription needed. Fastest and simplest option.
- Within 120 hours, or over 155 pounds: Ulipristal acetate (Ella) with a prescription. More effective in the later window and at higher body weights.
- Within 120 hours, any weight: Copper or hormonal IUD placed by a provider. Most effective option overall, with the bonus of long-term contraception.
If you’re unsure which option fits your situation, a pharmacist can help with levonorgestrel questions, and a clinic or telehealth provider can assess whether ulipristal or an IUD makes more sense. The priority is acting quickly with whichever method you can access first.