If you’ve had unprotected sex, the most time-sensitive step is emergency contraception, which works best the sooner you take it but can still prevent pregnancy up to five days afterward. Beyond pregnancy prevention, you’ll also want to get tested for sexually transmitted infections at the right time. Here’s what to do, in order of urgency.
Emergency Contraception: Your Options and Timing
You have up to five days (120 hours) after unprotected sex to use emergency contraception, but effectiveness drops with every hour you wait. There are three main options, and choosing the right one depends on how much time has passed, your weight, and whether you want ongoing birth control afterward.
The copper IUD is the most effective option at any body weight. Placed by a healthcare provider within five days of unprotected sex, it prevents pregnancy roughly 10 times more effectively than emergency contraceptive pills. A hormonal IUD may also work: one study found a pregnancy rate of just 0.3% with the hormonal IUD, compared to 1.4 to 2.6% for oral emergency contraceptive pills. Either IUD can then stay in place as your regular birth control for years.
If you’d rather take a pill, you have two choices. Levonorgestrel (sold as Plan B and similar brands) is available over the counter at pharmacies without a prescription. It works best within the first three days. After that, its effectiveness drops noticeably, and by days four and five, pregnancy rates climb. The other pill option, ulipristal acetate (sold as ella), requires a prescription but maintains its effectiveness better through the full five-day window. Within the first three days, the two pills perform similarly. After three days, ulipristal acetate is the stronger choice.
If You Weigh More
Body weight affects how well these pills work. Levonorgestrel may lose effectiveness at a lower weight threshold than ulipristal acetate, particularly for people with a BMI of 25 or higher. If that applies to you, ulipristal acetate is the better pill option, and the copper IUD is the most reliable choice regardless of weight. That said, taking levonorgestrel is still better than doing nothing, even if you’re in a higher weight range.
Side Effects of the Morning-After Pill
Emergency contraceptive pills can cause nausea, headaches, dizziness, fatigue, breast tenderness, and cramping. These effects are mild for most people. Your next period may come earlier or later than expected, and you might have some light spotting in the meantime. None of this means the pill didn’t work or that you’re pregnant. It’s simply your body adjusting to a concentrated dose of hormones.
When to Take a Pregnancy Test
A home pregnancy test won’t give you a reliable answer right away. The NHS recommends waiting at least 21 days after unprotected sex before testing. Testing earlier than that can produce a false negative because your body hasn’t had enough time to produce detectable levels of the pregnancy hormone. If your period is late and you’ve waited at least three weeks, take a test. If it’s negative but your period still hasn’t arrived after another week, test again.
STI Testing: What to Get and When
Unprotected sex carries the risk of sexually transmitted infections, but getting tested too soon can miss an infection that hasn’t had time to show up on a test. Each infection has its own window period, which is the minimum time between exposure and a reliable result.
Chlamydia and gonorrhea can be detected by urine sample or swab. Testing at one week catches most infections, but waiting two weeks catches nearly all of them. These are the most common bacterial STIs and are easily treated once detected.
Syphilis requires a blood test. One month after exposure catches most cases, but three months is the window that catches nearly all of them.
HIV detection depends on the type of test. A blood test that checks for both antigens and antibodies can catch most infections at two weeks, with six weeks covering nearly all cases. An oral swab test takes longer to become accurate: one month catches most infections, three months catches nearly all. If you’re concerned about HIV specifically, a blood-based test gives you a faster answer.
If you’re unsure what you were exposed to, a reasonable approach is to get tested for chlamydia and gonorrhea about two weeks after exposure, then follow up with syphilis and HIV testing at the one-month and three-month marks. Many sexual health clinics offer panel testing that covers all of these at once.
Symptoms to Watch For
Many STIs produce no symptoms at all, which is why testing matters even if you feel fine. But if symptoms do appear, here’s the general timeline:
- Chlamydia: symptoms typically start 5 to 14 days after exposure, often including unusual discharge or pain during urination
- Gonorrhea: symptoms can appear within 5 days in men and within 10 days in women, with similar signs to chlamydia
- Genital herpes: sores or blisters tend to appear within about 12 days of exposure
- Trichomoniasis: symptoms may show up between 5 and 28 days after exposure, often as itching, irritation, or unusual discharge
- HIV: flu-like symptoms (fever, sore throat, body aches, swollen glands) typically appear 2 to 4 weeks after infection
- Hepatitis: symptoms, when they occur, may take weeks to develop
The absence of symptoms does not mean you’re in the clear. Many people carry and transmit chlamydia, gonorrhea, and even HIV without ever noticing symptoms on their own. Testing is the only way to know for sure.
PEP for HIV Exposure
If you believe you may have been exposed to HIV, post-exposure prophylaxis (PEP) is a course of medication that can prevent infection. It needs to be started within 72 hours of exposure, and the sooner the better. You can access PEP through emergency rooms, urgent care clinics, or sexual health clinics. This is particularly relevant if your partner is HIV-positive or if you don’t know their status and the encounter was high-risk.
Practical Next Steps
Your priority right now depends on how recently the unprotected sex happened. If it was within the last five days and pregnancy is a concern, get emergency contraception as soon as possible. If it was within the last 72 hours and HIV is a concern, ask about PEP. Then mark your calendar for STI testing at two weeks (chlamydia, gonorrhea) and again at one to three months (syphilis, HIV). If pregnancy is a possibility, take a home test no earlier than 21 days after the encounter.
One episode of unprotected sex doesn’t guarantee pregnancy or infection, but taking these steps in the right order and at the right time gives you the best chance of catching and addressing anything early.