DoxyPEP: How to Use Doxycycline After Sex to Prevent STIs

DoxyPEP is a single dose of the antibiotic doxycycline — 200 mg taken within 72 hours after condomless sex — used to lower the risk of certain bacterial STIs, mainly syphilis and chlamydia CDC. It works on bacteria only and has no effect on HIV or other viruses. CDC currently recommends it for specific higher-risk groups rather than everyone.

What DoxyPEP is and how it works

DoxyPEP stands for doxycycline post-exposure prophylaxis: you take it after a possible exposure to prevent infection. You keep a dose of doxycycline on hand and take it after condomless sex. Doxycycline is a tetracycline antibiotic that's been used for decades to treat infections like chlamydia and early syphilis.

The mechanism is straightforward pharmacology. Doxycycline blocks bacterial protein synthesis, so it can stop a small number of bacteria from establishing an infection before they multiply. Taking it soon after exposure clears the organisms during the window when only a few are present, before symptoms or transmission begin. That's why doxypep is timed to the sexual encounter rather than taken on a daily schedule.

This is an antibacterial tool. It does nothing against HIV, herpes, HPV, or any viral infection, because antibiotics don't act on viruses. It covers a slice of bacterial risk and nothing else.

How well does DoxyPEP work?

In clinical trials, DoxyPEP reduced the risk of syphilis and chlamydia, and in some studies gonorrhea MMWR, 2024. The strongest and most consistent benefit is against syphilis and chlamydia, caused by organisms that remain quite susceptible to doxycycline.

The effect on gonorrhea is less consistent. Neisseria gonorrhoeae has a long track record of developing resistance to antibiotics, and tetracycline resistance is already widespread in some populations, so the protection seen in studies varies with local resistance patterns. That inconsistency is one reason DoxyPEP is framed as a targeted prevention tool.

How to use DoxyPEP and who it's for

The dose is 200 mg of doxycycline, taken as soon as possible and within 72 hours after sex. Don't take more than that in any 24-hour period, even if you have sex more than once. People keep a supply at home and take a single dose after a condomless encounter rather than a daily pill.

CDC guidance is for providers to discuss DoxyPEP with gay and bisexual men and transgender women who have had at least one bacterial STI — gonorrhea, chlamydia, or syphilis — in the past 12 months. A recent diagnosis signals ongoing exposure risk, so clinicians use that criterion to identify who's likely to benefit most.

For other groups, including cisgender women, there isn't yet enough evidence to weigh the benefits and harms, so DoxyPEP is not broadly recommended for everyone. The science is still maturing, and recommendations may broaden as more data come in. If you're not in the groups above but think you'd benefit, have that conversation with a clinician rather than deciding on your own.

1. Take 200 mg of doxycycline by mouth as soon as you can, ideally within 72 hours of condomless sex.
2. Don't exceed that dose within any 24-hour window, even with multiple encounters.
3. Keep your doses on hand so you're not scrambling to fill a prescription after the fact.
4. Take it with water and food to lower the chance of stomach upset, and avoid lying down right after.

Cost and how to get DoxyPEP

DoxyPEP requires a prescription, so start with a clinician — a primary care provider, a sexual health clinic, an LGBTQ+ health center, or one of the many telehealth services that now offer it. Doxycycline is a long-established generic antibiotic, which keeps it relatively inexpensive compared with many newer prevention drugs, and it's frequently covered by insurance. Public and community health clinics may dispense it at low or no cost.

Bundle the conversation with routine STI screening. When you ask a provider about DoxyPEP, you can also arrange to get tested at the same visit, so prevention and detection happen together.

What DoxyPEP does NOT protect against

This is the most important limit to understand. DoxyPEP targets bacterial infections only. It does not prevent HIV, herpes (HSV), HPV, hepatitis, or any other viral infection, and it isn't reliable against every bacterial STI either — its real-world impact on gonorrhea is uneven.

Because long-term effects on antibiotic resistance aren't yet fully understood, CDC continues to monitor resistance as DoxyPEP use grows. Repeated antibiotic exposure can, in theory, select for resistant bacteria, both the STIs themselves and other organisms in the body. So it's positioned as a focused tool for higher-risk people, not a routine pill for the general population.

How DoxyPEP fits with other prevention

DoxyPEP works best as one layer in a larger plan. Condoms remain the broadest single barrier, cutting the risk of both bacterial and viral infections that DoxyPEP can't touch. Vaccines matter too: HPV vaccination and hepatitis B vaccination prevent infections antibiotics never address. And for HIV specifically, PrEP is the dedicated tool; DoxyPEP does nothing against HIV.

Regular testing ties it together, because no prevention method is perfect and many STIs cause no symptoms. Timing matters. If you've had a specific exposure, here's when to test after exposure so you don't test too early and miss something.

When to talk to a clinician

Reach out if you fall into the groups CDC names — gay and bisexual men or transgender women with a bacterial STI in the past year — and want to discuss whether DoxyPEP fits your situation. Also talk to a provider if you've had a recent exposure and aren't sure what to do, if you develop symptoms like sores, discharge, or pain, or if you're considering DoxyPEP but aren't in a recommended group, since the evidence there is still limited. A clinician can confirm the right dose, check for drug interactions and allergies, and set up a sensible testing schedule.