Testing positive for a sexually transmitted infection is nothing to feel ashamed about: it’s a common—if unpleasant—part of being sexually active.

Still, most of us would probably prefer to avoid the discomfort of contracting an STI if we can. STIs can increase the risk of acquiring HIV and passing it on to others, which could turn routine bacterial infections into something much more serious.
 

Thankfully, there’s a prescription called DoxyPEP that can significantly reduce the risk of contracting certain STIs, especially for men who have sex with men, and trans women. DoxyPEP “stopped 76 percent of chlamydia and syphilis infections that would otherwise have happened,” while its “efficacy against gonorrhoea averaged 35 percent” one 2025 report found. 

So, what exactly is DoxyPEP, and who should take it? We talked to medical experts in Canada and the U.S. to learn more.
 

What is DoxyPEP?

DoxyPEP is short for doxycycline post-exposure prophylaxis. In simpler terms, it means using doxycycline as a post-exposure STI prevention measure.

Doxycycline itself is an antibiotic that’s been around since the 1960s and is part of the tetracycline family of antibiotics, according to Dr. Andrew Crone, an infectious disease specialist based in Chicago. He says it’s been used for decades to treat skin infections, certain kinds of pneumonia and even Lyme disease.
 

In the last few years, doxycycline has found a new application as “DoxyPEP,” which refers to the use of this antibiotic to help prevent sexually transmitted infections like chlamydia, syphilis and gonorrhea, primarily for men who have sex with men, and trans women.

How does it work?

You can think of DoxyPEP as a “morning after pill” for certain STIs. It’s meant to be taken soon after condomless oral or anal sex when you’ve been potentially exposed to an STI, Crone says.

By taking a strong dose of the antibiotic right after exposure to sexually transmitted bacteria, you can knock out an STI before you ever test positive for it—or even know that you have it. 
 

The medicine is effective in preventing chlamydia, syphilis and (to a lesser extent) gonorrhea, but not HIV or other STIs.

DoxyPEP is an as-needed medication. It is recommended that you take DoxyPEP within 24 hours of a sexual encounter for the highest efficacy. The sooner the better, but you can take it up to 72 hours after sex. 
 

When should I use it?

You don’t necessarily need to take DoxyPEP after every sexual encounter. It makes sense to take it after condomless sex, or anytime you feel you might be vulnerable to infection, but use your judgment. 

“You should use it if you feel it’s applicable,” Crone says, emphasizing that you don’t have to be stingy and save it for the highest-risk scenarios. “This isn’t [for] just the seediest of encounters.”
 

You don’t have to bring DoxyPEP to the hookup, either, says Devan Nambiar of the Gay Men’s Sexual Health Alliance (GMSH), a sexual health organization based out of Toronto. While it’s more effective the sooner you take it, it’s fine to wait until you get home to take your dose.
 

You shouldn’t take more than one dose within a 24-hour period. “If you have sex again within 24 hours of your last dose of doxycycline, take your next dose 24 hours after your last [one],” advises a fact sheet from GMSH.
 

Crone suggests taking DoxyPEP with food, but to avoid taking it with dairy or within two hours of ingesting calcium, antacids or multivitamins, all of which can reduce the drug’s efficacy.

Is it safe? What are the side effects?

Yes, doxycycline is a long-established antibiotic that is safe for most people. “This isn’t a new thing that we’re introducing,” Crone says.

While doxycycline’s use as DoxyPEP is only a few years old, the U.S. Centers for Disease Control and Prevention issued clinical guidelines for DoxyPEP in June 2024. In Canada, the BC Centre for Disease Control supports the use of DoxyPEP for men who have sex with men, as well as trans women, but there is no nationwide guidance for DoxyPEP.
 

There are some possible side effects from the use of DoxyPEP:

• It can cause gastrointestinal discomfort or nausea.
• It can make your skin more sensitive to the sun.
• It can cause acid reflux or irritation to your throat.
   

Who is it for?

DoxyPEP is targeted mostly at men who have sex with men, as well as trans women. That’s because the antibiotic works well in oral and anal tissues that can be exposed to bacteria during unprotected sex, according to Crone.
 

While DoxyPEP is theoretically safe for people assigned female at birth, Crone says there is less data on its efficacy in vaginal tissues. Several “studies in cis women engaging in vaginal sex found that DoxyPEP was ineffective in preventing chlamydia, gonorrhea and syphilis,” according to a fact sheet from the GMSH, which noted that “much remains to be further studied.” 

That said, cis women or trans men who primarily have oral and anal sex might be good candidates for DoxyPEP, according to Crone.
 

Does DoxyPEP increase antibiotic resistance? 

Maybe. There isn’t yet enough conclusive data to say definitively whether taking DoxyPEP increases your resistance to antibiotics.
 

Gonorrhea in particular is often already resistant to tetracyclines, the family of antibiotics that DoxyPEP belongs to, Crone says. That’s why tetracyclines are not used as first-line treatment for someone who tests positive for gonorrhea. While DoxyPEP might be able to prevent gonorrhea in some people, its effect is modest. “It could help, but don’t hang your hat on it helping,” Crone says.
 

How does it interact with other medications?

DoxyPEP’s interactions with other drugs are limited. The antibiotic might interact with dermatology medications such as Accutane Roche, Clarus, Epuris and Absorica LD, according to GMSH. It might also interact with acitretin, a psoriasis medication, as well as vitamin A (retinoids) for skin care.

You should let your doctor know about all the medications you are taking before starting DoxyPEP. And it’s probably not a good idea to hand out DoxyPEP at a sex party, where you don’t know everyone’s medication list, says Nambiar.
 

Where can I get DoxyPEP?

You should be able to get a prescription for DoxyPEP from your physician. If they’re not familiar with DoxyPEP, it might help to bring a fact sheet that explains this new use of doxycycline. “The primary care doctor is a great first step for most patients,” Crone says.
 

Often, DoxyPEP is prescribed alongside the HIV-prevention drug PrEP. If you don’t have a family doctor, or if your doctor doesn’t feel comfortable prescribing this medication, there are other ways you might be able to access it: Some cities have sexual health clinics dedicated to the LGBTQ2S+ community, where you might be able to receive a DoxyPEP prescription. And the antibiotic is generally available from online retailers like MISTR and Freddie.