Key takeaways
- CDC's 2024 guidelines recommend offering doxy-PEP to gay, bisexual, and other men who have sex with men, and transgender women, who've had at least one bacterial STI in the past 12 months.
- The dose is 200 mg of doxycycline, taken as soon as possible and within 72 hours after oral, vaginal, or anal sex, and never more than 200 mg in 24 hours.
- CDC recommends bacterial STI testing at the body sites of exposure at baseline and every 3–6 months while using doxy-PEP.
- Testing matters because doxy-PEP doesn't prevent every infection, and an infection that slips through still needs proper treatment.
- CDC hasn't made a doxy-PEP recommendation for cisgender women, cisgender heterosexual men, or some other groups because the evidence is insufficient.
Doxy-PEP, short for doxycycline post-exposure prophylaxis, means taking a single dose of the antibiotic doxycycline after sex to lower the chance of getting certain bacterial STIs. In 2024, CDC published its first clinical guidelines for doxy-PEP in MMWR Recommendations and Reports. Those guidelines make one thing clear: doxy-PEP is part of a broader sexual health plan, and regular STI testing stays in that plan.
This guide focuses on how testing fits in. If you're on HIV PrEP, many of these visits will overlap with your PrEP care. See the PrEP STI testing schedule.
Who CDC recommends doxy-PEP for
- Recommended: CDC says providers should counsel gay, bisexual, and other men who have sex with men (MSM) and transgender women (TGW) who've had at least one bacterial STI (syphilis, chlamydia, or gonorrhea) in the past 12 months, and offer doxy-PEP through shared decision-making.
- Could be discussed: MSM and TGW without a recent STI who are at higher risk, though the trials didn't directly study this group.
- No recommendation yet: CDC says it can't make a recommendation for cisgender women, cisgender heterosexual men, transgender men, and other queer and nonbinary people assigned female at birth, because evidence is insufficient. The only trial in cisgender women didn't show a significant reduction in bacterial STIs. For these groups, CDC advises clinicians to use clinical judgment and shared decision-making.
The dosing is specific: 200 mg taken as soon as possible, within 72 hours after oral, vaginal, or anal sex, and never more than 200 mg in 24 hours. Only use doxy-PEP with a prescription and guidance from a clinician.
Before you start: the baseline visit
The first visit sets your starting point. Expect testing for gonorrhea and chlamydia at each site you use for sex, a syphilis blood test, and HIV testing if you're not already on PrEP. Starting doxy-PEP with an untreated infection would mean that infection doesn't get proper treatment, which is one reason baseline testing comes first. It's also a good time to check hepatitis B and C screening and vaccination status. CDC recommends one-time hepatitis B and hepatitis C screening for all adults.
The testing schedule on doxy-PEP
CDC's guidelines call for:
| What | When | Details |
|---|---|---|
| Bacterial STI testing | Baseline, then every 3–6 months | Gonorrhea and chlamydia NAAT at the anatomic sites of exposure; syphilis blood test |
| HIV testing | Per current HIV screening recommendations | For people not on PrEP, CDC suggests considering HIV screening every 3–6 months |
| Reassessing doxy-PEP | Every 3–6 months | Whether you still need it, plus side effects and supply |
| Testing with symptoms | Any time | Don't wait for your scheduled visit |
"Sites of exposure" means the throat, rectum, and urogenital site as relevant to the sex you have. A urine-only test leaves throat and rectal infections unchecked. See testing after anal sex and testing after oral sex.
Why testing still matters on doxy-PEP
It doesn't prevent everything
Doxy-PEP reduces bacterial STIs, but it doesn't eliminate them. An infection that gets through, especially in the throat or rectum, may cause no symptoms. Regular site-specific testing is how it gets found.
Infections that get through need standard treatment
A single 200 mg dose after sex is prevention, not treatment. If you test positive, you need the standard treatment for that infection. For gonorrhea, that's an injection of ceftriaxone, not doxycycline. Don't try to treat yourself with extra doxy-PEP doses.
Syphilis can be silent
Early syphilis sores are often painless and can be hidden, for example in the rectum or mouth. Regular blood testing catches infections you wouldn't notice.
Antibiotic resistance is being watched
One of the concerns CDC's guidance discusses is antimicrobial resistance and other effects of repeated antibiotic use. Regular check-ins give your clinician a chance to review whether doxy-PEP is still the right choice for you.
It doesn't protect against HIV or viral STIs
Doxy-PEP targets bacterial STIs. It doesn't prevent HIV, herpes, HPV, or hepatitis. HIV prevention needs PrEP, condoms, or other strategies, and HIV testing stays on the schedule.
Doxy-PEP vs HIV PEP
They're easy to confuse. Doxy-PEP is a single antibiotic dose to lower bacterial STI risk. HIV PEP is a 28-day course of HIV medicines that must start within 72 hours after a possible HIV exposure. If you've had a possible HIV exposure, doxy-PEP won't help. Ask about HIV PEP urgently.
What your results mean while on doxy-PEP
- All negative: Keep going with your 3–6 month schedule, and reassess whether you still need doxy-PEP.
- Positive for chlamydia, gonorrhea, or syphilis: Get standard treatment for that infection, tell recent partners, and follow the retest guidance. For chlamydia and gonorrhea, CDC generally recommends a retest about 3 months after treatment, and anyone with throat gonorrhea needs a test of cure 7–14 days after treatment.
- Repeated infections despite doxy-PEP: Talk with your clinician about timing of doses, missed doses, and other prevention options.
If you aren't sure how to read your results, see what happens after a positive test.
What to bring to each check-in
- Roughly how many doses you've taken since your last visit.
- The types of sex you've had, so the right sites are tested.
- Any symptoms, including mild ones like sore throat, rectal discomfort, discharge, rash, or sores.
- Any side effects, such as stomach upset or sun sensitivity.
- Whether you have enough doses on hand.
Between visits
- Symptoms? Get tested now. Don't wait for the 3-month mark.
- Partner tells you they tested positive? Get tested and ask about treatment. Doxy-PEP may not have prevented infection. See your partner tested positive.
- Possible HIV exposure and you're not on PrEP? Ask about HIV PEP within 72 hours.
Keeping up with 3–6 month screening?
Lab-based STI testing with STDcheck
If you need to fill a gap between clinic visits, STDcheck lets you order lab-based tests online and give samples at a partner lab. Make sure the tests cover your exposure sites. Throat and rectal testing may need to go through your doxy-PEP prescriber.
Visit STDcheck.com →Frequently asked questions
How often should I get STI tested on doxy-PEP?
CDC recommends bacterial STI testing at the body sites of exposure at baseline and every 3–6 months, plus testing any time you have symptoms.
Does doxy-PEP mean I don't need STI testing?
No. Doxy-PEP lowers risk but doesn't prevent every infection, and infections that get through need standard treatment. Regular testing is part of CDC's recommendations.
Can I use doxy-PEP to treat an STI I already have?
No. The single 200 mg dose is for prevention after sex. A diagnosed infection needs the standard treatment for that infection. For gonorrhea, that's ceftriaxone.
Is doxy-PEP recommended for women?
CDC's 2024 guidelines say there's insufficient evidence to make a recommendation for cisgender women. Clinicians may use clinical judgment and shared decision-making.
Does doxy-PEP prevent HIV?
No. It targets bacterial STIs. HIV prevention uses PrEP, condoms, or HIV PEP after an exposure, and HIV testing should continue.
Sources
- CDC: Clinical Guidelines on the Use of Doxycycline Postexposure Prophylaxis for Bacterial STI Prevention (MMWR, 2024)
- CDC STI Treatment Guidelines: Gonococcal Infections Among Adolescents and Adults
- CDC: PEP guidance for clinicians
Guidance changes. When timing or treatment matters, check the current linked guidance or ask a clinician.
Disclaimer: This article is for informational purposes only and does not diagnose, prescribe, or replace individualized medical care. Testing and treatment decisions should be made with a qualified healthcare provider. Some links on this page are affiliate links; we may earn a commission at no extra cost to you.