What Is DoxyPEP? The New STI Prevention Pill, Explained

Updated May 2026 · 7 min read

DoxyPEP (doxycycline post-exposure prophylaxis) is a new strategy to prevent bacterial STIs like chlamydia, syphilis, and gonorrhea. You take a single antibiotic pill within 72 hours after sex. Clinical trials showed it reduced chlamydia by 88% and syphilis by 87%. Here’s everything you need to know.

How DoxyPEP Works

DoxyPEP stands for doxycycline post-exposure prophylaxis. Unlike PrEP (which you take before exposure to prevent HIV), DoxyPEP is taken after sex to prevent bacterial STIs. The concept is simple: take 200 mg of doxycycline (a common antibiotic) within 72 hours after oral, anal, or vaginal sex. Don’t take more than one dose in any 24-hour period, regardless of how many times you have sex that day.

Doxycycline has been used safely for decades to treat infections, acne, and other conditions. Using it as post-exposure prevention for STIs is what’s new.

How Effective Is DoxyPEP?

In the landmark DoxyPEP trial conducted in San Francisco and Seattle, 200 mg of doxycycline within 72 hours of condomless sex reduced the incidence of:

88%

Reduction in chlamydia

87%

Reduction in syphilis

55%

Reduction in gonorrhea

Not proven

For cisgender women (trial showed no significant reduction)

Two additional randomized trials confirmed similar effectiveness. The trial was stopped early because the protective effect was so significant that it would have been unethical to continue the control group without access to the treatment.

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Who Should Consider DoxyPEP?

The CDC published formal clinical guidelines in June 2024. The guidelines recommend providers discuss DoxyPEP with:

Gay, bisexual, and other men who have sex with men (MSM) and transgender women who have had at least one bacterial STI (chlamydia, syphilis, or gonorrhea) diagnosed in the past 12 months.

The CDC guidelines are intentionally narrow because those are the populations where clinical trials demonstrated clear effectiveness. A trial in cisgender women did not show significant STI reduction, so DoxyPEP is not currently recommended for cis women — though research is ongoing.

DoxyPEP is not a replacement for PrEP

DoxyPEP prevents bacterial STIs (chlamydia, syphilis, gonorrhea). PrEP prevents HIV. They protect against different infections and work well together. Many people use both — PrEP daily for HIV prevention, and DoxyPEP as needed after sex for STI prevention.

Where to Get DoxyPEP

MISTR offers DoxyPEP alongside PrEP. If you’re already a MISTR patient, ask your physician during your next consultation. If you’re new, DoxyPEP is available as part of your initial setup.

Freddie also provides DoxyPEP alongside PrEP services in the US.

Your primary care doctor or sexual health clinic can prescribe DoxyPEP. Doxycycline is a widely available, inexpensive generic antibiotic. If your provider isn’t familiar with DoxyPEP, you can share the CDC’s DoxyPEP guidelines.

How Much Does DoxyPEP Cost?

Doxycycline is a generic antibiotic that costs approximately $4–$20 for a 30-day supply at most pharmacies, even without insurance. It’s one of the cheapest antibiotics available. With insurance, the copay is typically $0–$5.

Through telehealth Some telehealth PrEP services and Freddie, DoxyPEP may be included at no additional cost alongside your PrEP care.

Concerns About Antibiotic Resistance

The biggest open question about DoxyPEP is whether widespread use of doxycycline could accelerate antibiotic resistance — making it harder to treat infections in the future. The CDC acknowledged this concern directly in their guidelines and committed to monitoring resistance patterns over time.

The guidelines are intentionally limited to the populations where DoxyPEP has proven effective, partly to minimize resistance risk. The CDC recommends STI testing every 3–6 months for DoxyPEP users to catch any breakthrough infections early, and providers should reassess the ongoing need for DoxyPEP at each visit.

For now, the public health consensus is that the STI prevention benefits outweigh the resistance risk for the recommended populations — but this is an active area of research.

Frequently Asked Questions

Can I take DoxyPEP and PrEP at the same time?

Yes. They prevent different infections — PrEP prevents HIV, DoxyPEP prevents bacterial STIs. There are no known drug interactions. Many people use both together.

Does DoxyPEP prevent HIV?

No. DoxyPEP only prevents bacterial STIs (chlamydia, syphilis, and to a lesser extent gonorrhea). For HIV prevention, you need PrEP. See our guide to free PrEP.

What are the side effects of doxycycline?

Common side effects include nausea, diarrhea, and sun sensitivity (you burn more easily). Taking it with food reduces nausea. These effects are generally mild and well-tolerated. Doxycycline has been used safely for decades.

Is DoxyPEP FDA-approved?

Doxycycline is FDA-approved for many uses, but not specifically labeled for STI prevention. Prescribing it for DoxyPEP is considered “off-label” use, which is common and legal. The CDC has published formal clinical guidelines endorsing this use for specific populations.

Does DoxyPEP work for women?

A clinical trial in cisgender women showed no significant reduction in bacterial STIs with DoxyPEP. The CDC’s current guidelines do not recommend DoxyPEP for cis women. However, some states like California have broader guidelines that suggest offering DoxyPEP via shared decision-making to all non-pregnant individuals at increased STI risk. Research is ongoing.