What Is DoxyPEP? The New STI Prevention Pill, Explained

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:

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.

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.

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 platforms like MISTR 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

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