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A morning-after pill to lower the risk of contracting a sexually transmitted infection (STI)

What is DoxyPEP?

A morning-after pill to lower the risk of contracting a sexually transmitted infection (STI)

Doxycycline Post-Exposure Prophylaxis (DoxyPEP) means taking the antibiotic doxycycline after sex to prevent getting a sexually transmitted infection (STI). It is a morning-after pill for STIs. Studies have shown that taking DoxyPEP reduces your chance of getting syphilis and chlamydia by about two-thirds, especially if you are a transgender woman (TGW) or a man who has sex with men (MSM).

DoxyPEP for STI Prevention

When should I take DoxyPEP?
Two 100 mg of doxycycline should ideally be taken within 24 hours, but no later than 72 hours after condomless sex. Condomless sex means oral, anal, or vaginal/front-hole sex where a condom is not used for the entire time.
What about when I have sex again?
If you have sex again within 24 hours of taking DoxyPEP you are still protected by your first DoxyPEP dose. However, If you have sex more than 24 hours after taking DoxyPEP then you should consider taking another dose.
How should I take DoxyPEP?
Take doxycycline with plenty of water or something else to drink so that it does not get stuck when you swallow. If your stomach is upset by doxycycline, taking it with food may help.
Some people are more sensitive to the sun when they take doxycycline, so wear sunscreen.
Please do not share doxycycline with others.
Avoid dairy products, calcium, antacids, or multivitamins 2 hours before and after taking doxycycline.

What are we still learning about DoxyPEP?

Does it affect normal (“good”) bacteria in our intestines?
Will DoxyPEP increase doxycycline resistance in bacteria that cause STIs?
Could it increase or decrease the bacteria that live on our skin (for example, staph), or cause bacterial resistance to doxycycline?
Although doxycycline has been used for decades, there is no known resistance to doxycycline in chlamydia or syphilis.

About 25% of gonorrhea in the US is already resistant to doxycycline; DoxyPEP may not work against these strains. The DoxyPEP study and other studies will help understand whether using DoxyPEP changes resistance in gonorrhea.


Please continue to get tested for STIs every 3 months and whenever you have symptoms.
If you are living with HIV, continue to take your medications and see your health care provider regularly.
DoxyPEP doesn’t protect against MPOX (monkeypox), HIV, or other viral infections. Talk to your health care provider about pre-exposure prophylaxis (PrEP) and post-exposure prophylaxis (PEP) for HIV prevention.
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