Syphilis, gonorrhea, and chlamydia – which are bacterial sexually transmitted infections (STIs) – have been on the rise in the U.S., including here in King County. DoxyPEP is a new tool in the safer sex toolbox, offering protection against these STIs for some people.
But what is DoxyPEP, who should consider it, and how well does it actually work? We sat down with Dr. Chase Cannon, one of the Medical Directors of Public Health – Seattle & King County’s Sexual Health Clinic at Harborview, to discuss DoxyPEP.
Dr. Chase Cannon is a Medical Director at Public Health’s Sexual Health Clinic at Harborview.
Q: What is DoxyPEP?
Dr. Cannon: DoxyPEP, which stands for doxycycline post-exposure prophylaxis, is the name for using a common antibiotic called doxycycline to reduce the risk of STIs. You take two doxycycline pills (or 200 mg) as soon as possible (ideally within 24 hours) after condomless oral, anal, or vaginal sex. It can be taken up to 72 hours after sex, but we think it is generally more effective if taken sooner.
Q: Who should consider using DoxyPEP?
Studies show that DoxyPEP can be very helpful for certain people at higher risk of STIs, including:
- Gay, bisexual, and other men who have sex with men (MSM), and transgender women who have had:
- one or more STIs in the prior year, OR
- condomless sex with multiple partners.
- In certain cases, DoxyPEP can also be used by cisgender women, transgender men, and nonbinary people who have a history of syphilis, or by people who may be anticipating having more sex in the near future.
Q: Is DoxyPEP safe?
This antibiotic has been used for many decades to treat everything from urinary tract infections to acne. Most people tolerate doxycycline well. Side effects may include stomach upset and sun sensitivity. Serious reactions are rare but possible. Talk with your healthcare provider to help determine if it’s right for you.
Q: How effective is DoxyPEP?
In clinical trials, DoxyPEP reduced the risk of syphilis by 77%, and chlamydia by 65%. However, it’s less effective against gonorrhea, likely due to the rise of antibiotic-resistant gonorrhea in Seattle and King County.
DoxyPEP does not protect against viral STIs like HIV, herpes, HPV, or mpox, so it should be used alongside other prevention strategies including condoms, vaccines for certain STIs, safer sex practices, pregnancy planning, testing for HIV/STIs, getting treated for STIs if you test positive, taking HIV PrEP or HIV medications to become and stay undetectable, and limiting your number of sex partners.
DoxyPEP may have some social and psychological benefits, as well. In clinical trials, people using DoxyPEP reported improved peace of mind and sexual pleasure, increased self-awareness about sexual behavior, and improved communication with sexual partners.
Q: Is DoxyPEP the same as HIV PrEP (pre-exposure prophylaxis) or PEP (post-exposure prophylaxis)?
No, and this is a common source of confusion. DoxyPEP will not prevent HIV infection. The medications used to prevent HIV are completely different. If you’re concerned about HIV exposure, talk to your provider about starting PrEP or accessing PEP immediately after a potential exposure.
Q: Is DoxyPEP lowering STI rates in King County?
We’ve begun to see declines in the number of new cases of syphilis and chlamydia in certain cities where DoxyPEP has been introduced, including Seattle.
Since DoxyPEP was endorsed by Public Health in early 2023, syphilis rates are down by almost 50% in King County. This is a very promising early trend and indicates that wider usage of DoxyPEP might continue to lower rates of syphilis and chlamydia.
Q: Are there concerns about antibiotic resistance?
Yes, some experts have expressed real concern about this. Widespread use of antibiotics can lead to drug-resistant bacteria that make some infections harder to treat. That’s why DoxyPEP is only recommended for people at ongoing, high risk of STIs, where the potential benefits outweigh the risks. It’s always a good idea to tell any healthcare provider who may prescribe medication for you that you’re taking DoxyPEP so they can make the best decision on which antibiotic to use if you ever need treatment for an infection.
Q: How does someone get started with DoxyPEP?
If you’re interested in DoxyPEP, talk with your primary care or other medical provider, or visit a sexual health clinic to get a prescription. In King County, the Public Health Sexual Health Clinic at Harborview Medical Center, and several community-based clinics, offer DoxyPEP to eligible patients. Some online services are also providing DoxyPEP now – this may be convenient, but not all services may be available to answer your questions or address your issues. At least in the beginning, it’s always best to talk with a provider about how to use DoxyPEP correctly as a part of your sexual health plan.
Final thoughts
DoxyPEP is an exciting new tool in the fight against bacterial STIs, particularly syphilis and chlamydia. But it’s not a catch-all solution, and it won’t protect you from all types of STIs.
If you think DoxyPEP might be right for you, talk to your healthcare provider or visit a local sexual health clinic. For more information on DoxyPEP, check out our DoxyPEP fact sheet in English or Spanish, as well as our updated 2025 DoxyPEP Guidelines for healthcare providers.
Originally published August 6, 2025.