For uncomplicated genital chlamydia, current CDC guidance prefers doxycycline (100 mg twice daily for 7 days) over single-dose azithromycin (1 g). Both cure most infections, but doxycycline clears rectal and urethral chlamydia more reliably. Azithromycin stays the go-to in pregnancy and when adherence is uncertain CDC Tx.
| Item | Reported cases |
|---|---|
| Chlamydia | 1,648,568 |
| Gonorrhea | 601,319 |
| Syphilis (P&S) | 53,007 |
What each option actually is
Both drugs are antibiotics that kill Chlamydia trachomatis, the bacterium behind the most commonly reported bacterial STI in the US — roughly 1.65 million reported cases in 2023, about 492 per 100,000 people, a rate that's stayed roughly flat across 2020–2023 CDC AtlasPlus, 2023. They get there differently.
Doxycycline is a tetracycline. The CDC-preferred regimen is 100 mg orally twice daily for 7 days — a full week of pills you take morning and evening CDC STI Guidelines, 2021. Because it sits at adequate levels in tissue over several days, it does steady work against bacteria hiding in the urethra and rectum.
Azithromycin is a macrolide. The chlamydia dose is 1 g orally as a single dose, watched in the clinic if needed. That simplicity is its biggest practical advantage, since nobody can forget day three of a course that's already over.
The key differences that decide it
In the 2021 STI treatment guidelines, the CDC downgraded azithromycin from co-equal to alternative for concrete reasons.
Cure rates differ by site. Microbiologic treatment failure in men was higher with azithromycin than with doxycycline, and the gap is widest for rectal infection. In a randomized trial of rectal chlamydia, doxycycline cured everyone treated while single-dose azithromycin cured about three in four — 100% versus 74% RCT, rectal CT. That difference drove doxycycline to first-line. It matters even for people without anal symptoms, because rectal infection is often completely silent and can reinfect the genital tract.
Adherence cuts the other way. A single dose can't be skipped or abandoned mid-course. A 7-day course only works if you finish it, so doxycycline's efficacy edge assumes you take every pill. If someone can't or won't complete a week of antibiotics, observed single-dose azithromycin may be the more reliable real-world choice.
Side effects and instructions differ. Doxycycline can upset the stomach and increases sun sensitivity, so take it with food and skip the tanning. Azithromycin is taken once but more commonly causes a wave of nausea or diarrhea from the larger single dose.
Pregnancy flips the preference. Tetracyclines like doxycycline aren't used in pregnancy because they can affect fetal teeth and bone. The pregnancy regimen is azithromycin 1 g as a single dose, with amoxicillin 500 mg three times daily for 7 days as an alternative.
Azithromycin vs doxycycline at a glance
| Doxycycline (preferred) | Azithromycin (alternative) | |
|---|---|---|
| Dose | 100 mg twice daily for 7 days | 1 g once (single dose) |
| CDC status (non-pregnant) | First-line | Alternative |
| Rectal infection cure | ~100% in trial | ~74% in trial |
| Adherence demand | Must finish a week of pills | None after one dose |
| Pregnancy | Not used | Preferred |
| Notable cautions | Take with food; avoid strong sun | Larger single dose, more GI upset |
| Abstain from sex | Until 7-day course is done | 7 days after the dose |
Which one applies to you
Most non-pregnant adults with uncomplicated genital chlamydia should get doxycycline as the default. It's the better bet if you might have a rectal infection, if you're a man, or simply because it's the more efficacious choice overall.
Choose azithromycin when you're pregnant, when adherence to a week of pills is a real concern, or when doxycycline isn't tolerated. Levofloxacin 500 mg once daily for 7 days is a further alternative your clinician may use in specific situations. None of this is self-prescribing — these doses come from a clinician who's confirmed your diagnosis and reviewed your situation.
One important exception: if testing points to lymphogranuloma venereum (LGV), an invasive form caused by C. trachomatis serovars L1–L3 that usually shows up as proctocolitis (mucoid or bloody rectal discharge, anal pain, and tenesmus — the urge to strain without passing stool), the course is much longer: doxycycline 100 mg twice daily for 21 days CDC LGV. LGV burden is highest among men who have sex with men, and standard 7-day treatment isn't enough.
The practical next step
Treatment only follows a diagnosis, so the real first step is testing. The optimal method is a NAAT (nucleic acid amplification test), and the experience is easy: a first-catch urine cup — hold your urine about an hour beforehand — or a self-collected swab, with no blood draw and no dreaded urethral swab. Results are often texted back within a few days. You can read the full how-to on our chlamydia testing & diagnosis page or simply get tested to start.
Timing trips people up. A common mistake is testing the morning after a hookup; a NAAT is most reliable about two weeks out, so an early negative can be falsely reassuring. If you're not sure when to go, check our guide on when to test after exposure.
Once you're treated, three things finish the job. Abstain from sex until the doxycycline week is done, or for 7 days after a single azithromycin dose. Get partners from the prior 60 days treated to stop 'ping-pong' reinfection; expedited partner therapy (giving you medication to deliver to a partner) measurably cuts repeat infection and is permissible in most but not all US states, so verify yours EPT RCT. And put a reminder in your calendar to retest in about three months, which catches chlamydia reinfection rather than treatment failure and is not a test-of-cure.
Cost rarely needs to be a barrier. Testing and treatment are free or low-cost at Planned Parenthood, health departments, and Title X clinics; at-home kits run roughly $50–150; and care is often $0 with insurance.
When to see a clinician
See a clinician promptly if symptoms appear — in women, abnormal discharge or burning on urination, and if it spreads, lower abdominal or low-back pain, fever, painful sex, or bleeding between periods; in men, penile discharge, burning on urination, or testicular pain and swelling. Untreated, chlamydia can cause pelvic inflammatory disease (infection of the uterus and tubes that can scar them), ectopic pregnancy, infertility, and chronic pelvic pain in women, and epididymitis (painful inflammation of the tube behind the testicle) in men About Chlamydia.
Also return to care if symptoms persist after treatment, if you couldn't finish the doxycycline course, or if you think you've been reinfected — those are the situations where a test-of-cure is warranted in non-pregnant people. Pregnant patients are handled differently: a test-of-cure about four weeks after finishing, plus a retest at three months. Anyone diagnosed with chlamydia should also be offered an HIV test.