Which STDs Does Doxycycline Treat? (Hint: The Big Ones)
Doxycycline is the workhorse STD antibiotic: first-line cure for chlamydia (100mg twice daily ×7 days), treatment for LGV and ureaplasma, penicillin-allergy alternative for syphilis, and the active ingredient in doxy-PEP — post-exposure prevention taken within 72 hours after high-risk encounters. It replaced azithromycin for chlamydia after head-to-head data showed superior cure rates.
What doxycycline treats
| Infection | Role | Regimen |
|---|---|---|
| Chlamydia | First-line cure | 100mg twice daily × 7 days |
| LGV | Standard (invasive chlamydia strain) | 100mg BID × 21 days |
| Syphilis (PCN-allergic) | Alternative to penicillin | 100–200mg daily × 14 days |
| Mycoplasma genitalium | Step 1 of staged therapy | Resistance-guided follow-up |
| Ureaplasma/M. hominis | Active when indicated | Per culture/PCR guidance |
| Doxy-PEP | Prevention after exposure | 200mg single dose ≤72h post-sex |
The azithromycin demotion story: trials showed doxycycline's chlamydia cure rates (~95%+) beating azithromycin's (~85–90%), especially rectal infections — guidelines updated accordingly.
Doxy-PEP: prevention's new chapter
Borrowing malaria-prophylaxis logic for STIs: taking 200mg doxycycline within 72 hours after condomless sex dramatically cuts acquisition — trial results showed roughly two-thirds reduction in syphilis and chlamydia among men who have sex with men, with gonorrhea reductions smaller.
- CDC now recommends it: for gay/bi men and transgender women with recent bacterial STI history.
- Dosing discipline matters: no more than one preventive dose per 24 hours; ongoing risk needs ongoing conversations, not daily pills (that's misuse).
- Trade-offs acknowledged: resistance pressure and GI side effects keep this targeted rather than universal (where it slots into full prevention).
Not for everyone: pregnancy excludes tetracyclines; children under 8 avoid them; regular sunburn-prone users get photosensitivity warnings. Clinician conversation required.
Taking it right
- Food helps: take with meals + full glass of water to dodge esophageal irritation and nausea.
- Stay upright 30 minutes after swallowing — doxycycline can burn the esophagus lying down.
- Sunscreen becomes mandatory: photosensitivity burns arrive fast.
- Finish the course even as symptoms evaporate by day three.
- Mind interactions: antacids/dairy/iron within 2 hours blunt absorption; birth-control interaction concerns are largely overstated but worth mentioning to your clinician.
Where doxycycline doesn't reach: gonorrhea (ceftriaxone's job), trich/BV (metronidazole), everything viral. Full drug map lives in treatment options overview; retest timing in window guide.
Frequently asked questions
Sources & further reading
- 📚 CDC — Chlamydia treatment — www.cdc.gov/std/treatment-guidelines/chlamydia.htm
- 📚 CDC — Doxy-PEP clinical considerations — www.cdc.gov/std/hcp/clinical-guidance/doxy-PEP.html
- 📚 NEJM — DoxyPEP trial results — www.nejm.org. Lautenschlager et al. 2022