What is Doxycycline as STI PEP?

Let’s break it down:

• Doxycycline, also called simply “doxy”, is an antibiotic. It’s been in use since 1967 to treat acne, UTIs, and other infections. 
• STI stands for Sexually Transmitted Infection (also commonly called STDs).
• PEP stands for Post-Exposure Prophylaxis. Post-exposure prophylaxis, also known as post-exposure prevention, is any preventive medical treatment started after exposure to a pathogen in order to prevent the infection from occurring. You may have heard of PEP used to prevent HIV after exposure to the virus — this is a different medication from doxycyline, but it’s used similarly.

Using doxy as STI PEP involves taking 200 mg of doxycycline, ideally within 24 hours but no later than 72 hours, after condomless oral, anal, or vaginal sex. The sooner you can take it after sexual contact, the better!

What STIs does it help with?

Since doxycycline is an antibiotic, it will only be helpful in preventing bacterial STIs. So far, it has primarily been studied for prevention of gonorrhea, chlamydia, and syphilis. It will not provide protection for viral STIs, such as HIV, HPV, or herpes (HSV 1 & 2). It is also not the same kind of medicine used in PEP for HIV, and should not be used in place of HIV PEP or PrEP.

Condoms are still the most effective way to prevent the transmission of STIs.

Who can take it?

Doxy as STI PEP is effective in adults assigned male at birth (such as cisgender men and transgender women) and has been primarily studied in gay, bisexual, and other men who have sex with men (GBMSM) and people living with HIV.

So far, it has not been found to work for those assigned female at birth (such as cisgender women and transgender men). Researchers aren’t sure why, but it’s possible that results were ineffective due to participants in the study not taking the medicine as prescribed. New studies are ongoing to find out more.

No studies have yet looked at doxy as STI PEP specifically with nonbinary or intersex people. It has also not been studied in adolescents. 

How effective is it?

An April 2023 NEJM article showed doxycycline as STI PEP reduced syphilis by 87%, chlamydia by 88%, and gonorrhea by 55% in individuals taking HIV PrEP and reduced syphilis by 77%, chlamydia by 74%, and gonorrhea by 57% in people living with HIV. These results are remarkable. It’s important to note that it’s most effective when taken within the first 24 hours after exposure, and must be taken within 72 hours to work.

While results vary somewhat from study to study, they have consistently found a significant decrease in transmission rates when using doxy as STI PEP as prescribed.

What about antibiotic resistance?

There are a lot of factors to consider when it comes to antibiotic resistance and using doxy as STI PEP. While antimicrobial resistance is an important threat to watch, many experts also emphasize that using doxy as STI PEP for a specific demographic of people pales in comparison to the use of antibiotics in other industries.

For context, doxycycline has already been in use as PEP for other infections, like malaria and Lyme’s disease, and is also prescribed long-term for the treatment of acne. Hesitancy to use it for STIs is likely rooted in stigma.

If you have concerns, talk with your healthcare provider and see what they recommend. This article also breaks down the considerations.

How do I get it?

Doxycycline currently requires a prescription in the United States, so you’ll need to see a healthcare provider to get it. If you’re an adult who was assigned male at birth and would like to know more, talk to your provider and tell them you’re interested in taking doxycycline as PEP for STIs. You can also contact a local STI clinic and see if they are offering it.

It’s important to continue to get regularly tested for STIs if you’re sexually active, especially if you have multiple and/or anonymous partners — try scheduling a routine STI visit and then bring up doxy as STI PEP during your time with your provider. Since it needs to be taken soon after sexual contact, it’s best to be prepared ahead of time if you can. Need help finding a clinic? Try this locator.

If you’re a provider interested in learning more, check out our Doxy as STI PEP Command Center.