What is DoxyPEP? The antibiotic taken after sex to prevent STIs
DoxyPEP is one dose of the antibiotic doxycycline within 72 hours after sex. Trials show it cuts syphilis and chlamydia by over 70%. Who it's for and how to take it.
Key points
- DoxyPEP means doxycycline post-exposure prophylaxis: taking the antibiotic doxycycline after sex to lower the chance of catching certain bacterial STIs.
- The dose is 200 mg, once, within 72 hours of sex, the sooner the better.
- In trials it cut syphilis and chlamydia by more than 70%, and gonorrhoea by about half.
- It does not prevent HIV. For that, see PrEP and PEP.
- It is newer than PrEP, and guidelines so far recommend it for specific groups.
How does it work?
Doxycycline is an old, cheap, widely used antibiotic. It has been used for decades to treat chlamydia, among many other things. The idea behind DoxyPEP is simple: if you take a dose soon after sex, it can kill the bacteria that cause syphilis, chlamydia and gonorrhoea before they settle in.
How do you take it?
The US Centers for Disease Control and Prevention (CDC) guidance is:
- 200 mg of doxycycline, taken as soon as possible after oral, vaginal or anal sex, and within 72 hours
- no more than 200 mg in any 24 hours
Practical tips from the same guidance: take it with plenty of water and some food, don’t lie down for an hour afterwards (it can irritate the throat on the way down), avoid dairy, antacids and supplements containing calcium, iron or magnesium for two hours either side, and use sunscreen, because doxycycline can make skin more sensitive to the sun.
How well does it work?
Three large trials, summarised in the CDC’s 2024 guidelines, found:
| Infection | Reduction with DoxyPEP |
|---|---|
| Syphilis | More than 70% |
| Chlamydia | More than 70% |
| Gonorrhoea | About 50%, and it varied between studies |
Gonorrhoea is the weak spot. In many places gonorrhoea is already resistant to this family of antibiotics. In one French trial, every gonorrhoea sample tested at the start was already resistant.
Who is it recommended for?
- United States (CDC, 2024). Gay, bisexual and other men who have sex with men, and transgender women, who have had syphilis, chlamydia or gonorrhoea in the past 12 months, should be counselled that DoxyPEP is an option.
- United Kingdom (BASHH, June 2025). The first UK national guideline recommends offering DoxyPEP, mainly to prevent syphilis, to gay and bisexual men and transgender women at higher risk, for example after a recent bacterial STI or with multiple new partners.
What about everyone else? The one trial in cisgender women, in Kenya, found no significant reduction in STIs. Researchers suspect the main reason was that few participants were actually taking the pills: doxycycline showed up in hair samples from only 29% of them. The CDC’s position is that there is “insufficient evidence” to weigh benefits and harms in other groups. That means not yet known, not doesn’t work. Doxycycline is also not used during pregnancy.
What are the concerns?
Antibiotic resistance. This is the main open question. Using more of an antibiotic can push bacteria to resist it. In one US trial, the share of gonorrhoea that was resistant to this drug family rose from 24% to 30% among people taking DoxyPEP. The CDC says studies so far can’t tell us the long-term effect. This is why guidelines target DoxyPEP at people most likely to benefit, rather than everyone.
Side effects. Mostly stomach upset and sun sensitivity. In one trial, stomach side effects were reported by 53% of people taking DoxyPEP compared with 41% of those who weren’t.
It isn’t a replacement for testing. The CDC recommends STI and HIV tests every 3 to 6 months while using it. DoxyPEP lowers risk; it doesn’t remove it.
What it doesn’t cover
HIV, mpox, herpes, HPV, hepatitis A, B and C. For those: PrEP for HIV, vaccines for hepatitis A and B, HPV and mpox, and condoms.
Can I get DoxyPEP while travelling?
It depends heavily on where you are. Some clinics offer it routinely, some have never heard of it, and in some countries guidelines don’t yet support it. On our clinic pages, DoxyPEP is listed as its own line, with the date we checked. If you already use it at home, the simplest approach is to bring your supply with you in its original packaging. Doxycycline for DoxyPEP is also sold for delivery by PrEP Online, alongside PrEP; check your country’s import rules first.
Browse clinics by country, or see how it compares: PEP vs PrEP vs DoxyPEP.
Sources
Checked 19 September 2026.
- CDC, Doxy PEP for bacterial STI prevention
- CDC, Guidelines for the use of doxycycline postexposure prophylaxis for bacterial STI prevention, 2024
- BASHH, UK national guideline for the use of DoxyPEP for the prevention of syphilis, 2025
Quick answers
How do you take DoxyPEP?
One 200 mg dose of doxycycline as soon as possible after sex, and no later than 72 hours after. Don't take more than 200 mg in any 24-hour period.
What does DoxyPEP protect against?
Syphilis and chlamydia, both reduced by more than 70% in trials, and gonorrhoea to a lesser and less reliable degree. It does not protect against HIV, mpox, herpes, HPV or hepatitis.
Who is DoxyPEP recommended for?
US and UK guidelines recommend it for gay, bisexual and other men who have sex with men, and transgender women, who have had a recent bacterial STI or are otherwise at higher risk. There isn't yet enough evidence to recommend it for other groups.
Is DoxyPEP the same as PEP?
No. PEP is a 28-day course of HIV medicine. DoxyPEP is a single dose of an antibiotic against bacterial STIs. The names are similar but they do different jobs.
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