This page is general health information, not medical advice. It cannot tell you whether you have an infection. A clinician can, and the testing options on this site are a good place to start.

Doxy-PEP is a way to lower the chance of getting certain bacterial infections after sex. It is a single antibiotic, doxycycline, taken after sex as a clinician directs. You will also see it written as doxy pep or DoxyPEP. All three mean the same thing.

This guide covers what the medicine is, what research suggests, who CDC says it is recommended for, and where to ask about it in Houston. It is not a substitute for a conversation with a clinician, and it does not replace testing.

Key points

Doxy-PEP is prescription only. A clinician decides whether it fits your situation.
CDC's 2024 guidance recommends it for specific groups, described below.
CDC says to take it within 72 hours after sex, and sooner is better.
It targets some bacterial STIs. It does not prevent HIV, herpes, HPV or mpox.
Regular testing still matters while using it.

What doxy-PEP is

PEP stands for post-exposure prophylaxis. That means a medicine used after a possible exposure to lower the chance of infection. HIV has its own PEP, which is a different treatment. Doxy-PEP refers only to doxycycline used this way against bacterial STIs.

CDC added doxy-PEP to its STI guidance in 2024, building on the CDC STI Treatment Guidelines from 2021. The recommendation came after several clinical trials looked at whether doxycycline taken after sex could lower infection rates.

The science: what doxycycline is

Doxycycline is a semi-synthetic antibiotic in the tetracycline class. Its core structure is a four-ring chemical framework shared by that family. Manufacturers make it by modifying a natural tetracycline compound.

It works by binding to the small subunit of the bacterial ribosome. The ribosome is the structure bacteria use to build proteins. When doxycycline blocks it, the bacteria cannot make what they need to grow and multiply. This is called a bacteriostatic effect, because it stops growth rather than directly killing the cell.

Doxycycline has been used for decades. Clinicians already prescribe it for several infections, and CDC's 2021 guidelines list it as part of treatment for chlamydia. That long track record is one reason researchers tested it for prevention.

What research suggests

CDC's 2024 guidance summarizes trials of doxycycline taken after condomless sex. Research suggests the approach lowered the number of syphilis and chlamydia infections by a large margin among the groups studied. Gonorrhea infections were lowered by a smaller margin.

The difference matters. Some gonorrhea bacteria already carry resistance to tetracycline-class drugs, which limits how well doxycycline can work against them. CDC describes the gonorrhea benefit as more modest than the benefit for syphilis and chlamydia.

These findings are observations from specific study populations. They do not mean any one person will or will not get an infection. Trials also had limits, including who was enrolled and how long people were followed.

Who CDC recommends it for

CDC's 2024 guidance recommends doxy-PEP for gay, bisexual and other men who have sex with men, and for transgender women, who have had at least one bacterial STI in the past 12 months. The bacterial STIs counted are syphilis, gonorrhea and chlamydia.

CDC also says clinicians can discuss doxy-PEP with other people through shared decision-making. That means you and a clinician talk through your history, your preferences and the benefits and risks. For groups outside the recommendation, CDC describes the evidence as limited. One trial in cisgender women did not show a clear benefit, so CDC did not make a recommendation for that group.

Group	CDC 2024 position
Men who have sex with men and transgender women with a bacterial STI in the past 12 months	Doxy-PEP recommended
Others, including cisgender women and heterosexual men	No recommendation; a clinician can discuss it case by case

If you are unsure which row describes you, a clinician can walk through it with you. Anyone of any gender or orientation can ask the question.

The 72-hour window

CDC says doxy-PEP should be taken within 72 hours after condomless oral, vaginal or anal sex. The sooner it is taken inside that window, the better. A clinician will explain the timing and the amount for your situation. This guide does not list doses or schedules, because that belongs in a prescription conversation.

The medicine is used after sex. It is not a daily preventive pill like HIV PrEP, and it is a separate decision from PrEP.

What it prevents and what it does not

CDC describes doxy-PEP as aimed at three bacterial infections: syphilis, chlamydia and, to a lesser degree, gonorrhea.

It does not prevent:

HIV
Herpes
HPV
Mpox
Hepatitis B or C
Trichomoniasis

These are viral or other infections that doxycycline is not expected to stop. HIV, herpes and HPV are not curable but are treatable or manageable. Bacterial STIs and trichomoniasis are curable with treatment from a clinician.

Doxy-PEP also does not replace condoms, vaccines or HIV PrEP. It is one tool among several. Condoms lower the chance of many infections, including ones doxy-PEP does not cover.

Safety profile and contraindications

Doxycycline is a well-studied antibiotic, and CDC's 2024 guidance reports that side effects in the trials were generally mild. Possible effects of tetracycline-class drugs include:

Upset stomach or nausea
Heartburn or irritation of the esophagus
Extra sensitivity to sunlight, which matters in a Houston summer
Yeast infections in some people

A clinician will ask about your health history before prescribing. Tetracyclines are generally avoided in pregnancy, and they are not used the same way in young children. Allergies, other medicines and liver or kidney conditions are also worth mentioning. Some supplements and antacids can interfere with how the body absorbs doxycycline, so ask a pharmacist or clinician about timing.

If you are pregnant, could become pregnant or are breastfeeding, tell the clinician at the start. They can explain options that fit your situation.

Resistance concerns

Any time antibiotics are used more widely, bacteria can adapt. CDC's 2024 guidance names resistance as a real concern. Doxycycline resistance already exists in some strains of gonorrhea. Researchers are also watching other bacteria, such as the ones that cause staph infections, for changes.

For this reason CDC recommends that clinicians prescribe doxy-PEP to the groups where benefit is best supported. It also asks clinicians to keep monitoring resistance over time. Using the medicine only as prescribed is part of protecting its usefulness for everyone.

Sourcing and quality indicators

Doxy-PEP in the United States is prescription only. The quality markers are simple:

It comes from a licensed clinician who has reviewed your history.
It is filled by a licensed pharmacy.
It comes with clear labeling and instructions from the pharmacist.
It is followed up with testing and check-ins.

Antibiotics from unverified sellers or leftover from an old illness can be the wrong medicine, the wrong strength or expired. Asking a clinician is the safer route, and it lets them check for interactions.

Testing still matters

CDC's 2024 guidance pairs doxy-PEP with regular STI testing. That includes testing for syphilis, gonorrhea and chlamydia at the visits when it is prescribed and at follow-up visits, typically every few months. HIV testing and PrEP conversations belong in the same visit.

A test is the only way to learn about your status. Doxy-PEP does not tell you anything about whether an infection is present. Only a clinician and a test can do that.

Houston numbers in context

The Texas Department of State Health Services publishes yearly STD surveillance reports. Its 2022 report counts 31,406 chlamydia cases in Harris County, a rate of 656.9 per 100,000 people. The statewide 2022 rate in the same report was 519.9 per 100,000.

For gonorrhea, the same report lists 12,935 Harris County cases, a rate of 270.6 per 100,000, compared with 207.0 statewide. It also records 5,670 syphilis cases of all stages in Harris County in 2022. The report does not publish a county rate for syphilis.

These are reported cases from 2022, the latest year in that report. Reported cases reflect who got tested as well as who was infected, so treat them as a rough picture rather than a precise one. Texas requires clinicians and labs to report chlamydia, gonorrhea, syphilis and HIV to public health, according to the 2026 DSHS list of notifiable conditions.

Where to ask about doxy-PEP in Houston

Legacy Community Health lists DoxyPEP among the services at its Montrose location, 1415 California St., Houston, TX 77006. The phone number is (832) 548-5100. Legacy says its HIV, syphilis and hepatitis C testing is free and that its services are open to all regardless of ability to pay. Its page does not state a price for a full STI panel, so ask the clinic about costs when you call.

Legacy also offers walk-in HIV, syphilis and hepatitis C testing. A full STI panel is available as appointments allow, according to Legacy.

The Houston Health Department's health centers list STD testing and treatment, plus PrEP and nPEP by appointment at 832-395-9800. The pages we reviewed do not mention doxy-PEP. The department says its centers moved to appointment-encouraged scheduling on September 1, 2026, with walk-ins seen as capacity permits. Call 832-393-4220 to ask what each center offers and what it costs on its sliding scale.

Harris County Public Health's Antoine Clinic, 5815 Antoine Dr., Houston, TX 77091, offers free STI testing, HIV testing and PrEP, with phone 832-927-7350. Its page does not mention doxy-PEP, so ask directly. The county lists Friday as closed, so confirm hours before you go.

Not every clinic lists doxy-PEP, and offerings change. For clinic-by-clinic details on testing, see the Houston guide to where to get tested and what it costs.

What to ask at your visit

Does this clinic prescribe doxy-PEP, and does my history fit CDC's recommendation?
Which tests do you recommend now, and how often afterward?
Is there anything in my health history or medicines that matters?
What should I do if I get side effects?
What does the visit cost, and are there sliding-scale or free options?

You do not need to explain your life to get care. Clinicians in public health settings hear these questions every day and are there to help, not judge.

Next step: get tested

Testing is the place to start, whether or not doxy-PEP is right for you. CDC's testing locator at gettested.cdc.gov can help you find options. In Houston, the clinics above offer free or sliding-scale testing. Call ahead to confirm hours and what is available that day.

Doxy-PEP in Houston: Who It Is For and How to Get It