This ‘morning after’ pill could prevent STIs from unprotected sex

The same antibiotic you'd take for strep or Lyme will fight chlamydia and syphilis before they get serious.
Doxycycline antibiotic pill for STI and STD prevention on a coral background
STI rates keep rising—Doxy-PEP could help. Deposit Photos

There are now two morning after pills you can pick up after a night of intimacy. Everyone’s familiar with the emergency contraceptive Plan B, but doctors are also pushing for a new treatment called Doxy-PEP to stop the spread of bacterial sexually transmitted infections (STIs) right after unprotected sex.

“In the old days when you had unprotected sex, most worries were on getting pregnant, so you took the morning after pill. This is kind of like the morning after pill, but to prevent getting specific STDs,” says Adi Davidov, an OBGYN at Staten Island University Hospital at Northwell Health.

The US is long overdue for a new STI-prevention strategy. The latest numbers from the Centers for Disease Control and Prevention (CDC) report more than 2.5 million new cases of chlamydia, gonorrhea, and syphilis in 2021. Syphilis, in particular, rose 32 percent from the year prior. 

“The STIs have really been exponentially increasing across the US for the last decade,” says Philip Chan, an infectious disease physician and the medical director for the Rhode Island-based health clinic Open Door Health. Recent studies on Doxy-PEP have shown it prevents certain bacterial infections; Chan is using this data to help the CDC develop guidelines on prescribing the drug and address concerns of antibiotic resistance and superbugs

[Related: A guide to preventing, spotting, and managing STIs]

Doxy-PEP is currently available as a prescription medication for anyone in the US. But just like Plan B, it’s only effective if you understand how to use it properly.

What is Doxy-PEP and how does it work?

Doxy-PEP stands for doxycycline post-exposure prophylaxis. It’s a one-time pill that contains 200 milligrams of the widely approved antibiotic doxycycline. In general, the drug wipes out bacterial infections by keeping germs from producing the essential proteins they need to survive.

The most ideal time to get treated with Doxy-PEP is within 24 hours of having sex. Jeffrey Klausner, an infectious disease specialist at the Keck School of Medicine of USC who has spearheaded multiple studies on STIs, says the current research estimates a 70 percent reduction in the risk of infection when taking the pill. “The studies went up to 72 hours, so we don’t really know what the long window is [for effectiveness]. The sooner you take it, the better.” 

Experts agree Doxy-Pep should be used as a contingency rather than as an alternative to condoms. Klausner says this is a medium-term solution until vaccines for STIs like gonorrhea and syphilis bring an end to these nuisances.

What are the side effects of Doxy-PEP?

Since 1967, doxycycline has been a popular antibiotic for getting rid of various disease-causing bacteria, from urinary tract infections to gum disease. But it’s not a perfect remedy. For example, the drug causes the user’s skin to become more sensitive, increasing the likelihood of a severe sunburn when outside.

In very rare situations, Klausner warns that Doxy-PEP can get stuck in a person’s food pipe, “particularly if you take it right before you go to bed.” If it does not travel all the way to the stomach, it can irritate the esophagus and potentially cause a hole or ulcer. To minimize this risk, take the pill at least half an hour before bed and with a full glass of water. You’ll also want to avoid alcohol when taking Doxy-PEP as it can lower the effectiveness of the antibiotic.

To be on the safe side, get a prescription if you’re worried about a possible infection after unprotected sex. Just be aware there are some side effects and precautions you need to follow when using the medication.

Who can take Doxy-PEP?

Anyone who’s had unprotected sex, had experiences with STIs in the past, or had multiple partners could benefit from Doxy-PEP. While there are no age restrictions, parental consent might be required for minors, just like with STI testing. The pill may be especially useful for gay and bisexual men: According to the CDC, this population makes up a disproportionate amount of STI cases. 

The treatment can also help give peace of mind to people who are trying to get pregnant and not using condoms, but still worried about STIs, says Davidov. However, he emphasizes it’s better to have sex with a partner who has tested negative for STIs.

Keep in mind Doxy-PEP only works on bacterial infections like gonorrhea, syphilis, and chlamydia, not viral ones like herpes or HIV. The pill also does not work on individuals who’ve already tested positive for those conditions.

Where to find Doxy-PEP

Like with any antibiotic, you need a prescription to get Doxy-PEP. But your primary care doctor might not be familiar with it, Chan explains. He recommends visiting a sexual health clinic that may be more well-versed in the latest treatment options. 

Some clinics will give out Doxy-PEP for free; if they don’t, insurance will likely cover the cost of the preventative treatment. Even if there is a co-pay or deductible, Klausner says it should not be financially burdensome as doxycycline is one of the cheapest antibiotics available.

Will Doxy-PEP make antibiotic resistance worse?  

The World Health Organization lists antibiotic resistance as one of the top 10 global health problems. Resistance to doxycycline in particular would be a major blow, in particular, because it might limit the ability to treat other infections like malaria and Lyme disease.

A study published this year in the New England Journal of Medicine looked at Doxy-PEP’s effectiveness and safety among men who had sex with men and transgender women who took the medicine within 72 hours of unprotected sex. While doxycycline reduced the risk of bacterial STIs by two-thirds, the authors did observe a few signs of antibacterial resistance. Notably, they found that some gonorrhea strains survived the antibiotic treatment. Doxy-PEP also cut the number of Staphylococcus aureus, a bacterium commonly found in the skin, in half. However, the germs that did persist grew to be antibiotic-resistant a year later—a concern given that doxycycline is usually prescribed to treat Staphylococcus aureus skin infections.

“It’s really about weighing the pros and the cons, and with the increasing incidence of STIs over the last decade, it’s clear we need to do something,” Chan explains. 

[Related: Why the FDA finally approved a condom for anal sex]

For now, the research linking antibiotic resistance to Doxy-PEP is still under investigation. But there is one silver lining: Clinical trials and real-life observations on the pill show that it works well and could improve the sexual health of millions. Just be sure to save it for emergencies.