The antibiotics used to treat an STI depend entirely on which infection you have. Chlamydia, gonorrhea, syphilis, and trichomoniasis each require different medications, and some need a single dose while others take a week or more. Here’s what’s currently recommended for each major bacterial and parasitic STI.
Chlamydia
Chlamydia is the most commonly reported bacterial STI, and it’s treated with doxycycline: 100 mg taken twice a day for seven days. This is the current first-line recommendation from the CDC, which shifted away from the single-dose azithromycin that was previously standard. The change happened because doxycycline has proven more effective, particularly for rectal chlamydia infections that single-dose azithromycin often missed.
If you can’t take doxycycline (for example, during pregnancy), alternatives exist, but doxycycline remains the go-to for most people. You should avoid sex until you’ve finished the full seven-day course to prevent passing the infection to a partner.
Gonorrhea
Gonorrhea is treated with a single injection of ceftriaxone, a powerful antibiotic given as a shot in the muscle. The standard dose is 500 mg for people under about 300 pounds, or 1,000 mg for those above that weight. There is no reliable oral pill option for gonorrhea anymore, which is largely due to rising antibiotic resistance.
This is one of the more concerning STIs from a resistance standpoint. Gonorrhea has developed resistance to nearly every antibiotic ever used against it, including ciprofloxacin and, increasingly, azithromycin. A 2024 World Health Organization report covering nine countries showed rising resistance to both ceftriaxone and azithromycin. This is why the treatment has been narrowed to a single injectable drug rather than oral options: it’s one of the few antibiotics that still works reliably.
Syphilis
Syphilis is one of the few STIs still treated with penicillin, and it remains remarkably effective. The specific form is a long-acting injectable penicillin given as a shot.
For early syphilis (primary, secondary, or early latent stage), a single injection of 2.4 million units clears the infection. For late latent syphilis, where the infection has been present for more than a year or for an unknown duration, treatment requires three injections of 2.4 million units each, given one week apart, for a total of 7.2 million units. The stage of infection determines the treatment length, which is one reason early testing matters so much.
Trichomoniasis
Trichomoniasis is caused by a parasite rather than a bacterium, but it’s still treated with antibiotics, specifically metronidazole or tinidazole. Interestingly, the recommended regimen differs between men and women.
For women, the CDC recommends metronidazole 500 mg twice daily for seven days. For men, a single 2-gram dose of metronidazole is considered sufficient. The difference reflects how the parasite behaves differently in male versus female anatomy. Tinidazole, given as a single 2-gram dose, is an alternative for both.
One important practical note: you must avoid alcohol while taking metronidazole and for at least 48 hours after your last dose. For tinidazole, that window extends to 72 hours. Mixing alcohol with either drug can cause severe nausea, vomiting, and flushing.
Mycoplasma Genitalium
Mycoplasma genitalium is a lesser-known STI that causes symptoms similar to chlamydia, including burning during urination and discharge. It’s harder to treat than most STIs because it has high rates of antibiotic resistance, and treatment uses a two-stage approach.
The first stage is always doxycycline for seven days, which reduces the amount of bacteria present. The second stage depends on whether the infection is resistant to certain antibiotics. If resistance testing shows the bacteria respond to azithromycin, a high-dose course of azithromycin follows. If the bacteria are resistant to azithromycin (which is common), moxifloxacin is used for seven days instead. When resistance testing isn’t available, which is the case for most clinics in the U.S. since commercial tests for resistance markers aren’t yet widely accessible, moxifloxacin is typically prescribed as the second-stage drug. This resistance-guided approach achieves cure rates above 90%.
Pelvic Inflammatory Disease
Pelvic inflammatory disease (PID) develops when an STI, usually chlamydia or gonorrhea, spreads into the uterus, fallopian tubes, or ovaries. Because multiple types of bacteria are often involved, PID requires a combination of antibiotics rather than a single drug.
Mild to moderate PID is typically treated on an outpatient basis with a one-time injection of ceftriaxone plus a 14-day oral course of doxycycline and metronidazole. Severe cases that require hospitalization use IV antibiotics, then transition to oral medications once symptoms improve, for a total of 14 days of treatment. The longer duration and multiple drugs reflect how much more serious PID is compared to an uncomplicated STI.
What to Know After Treatment
Finishing your antibiotics doesn’t mean you’re immediately in the clear. If you received a single-dose treatment, wait at least seven days before having sex again. If you took a multi-day course, wait until you’ve completed every dose. Having sex too soon is one of the most common reasons people test positive again shortly after treatment.
Your sexual partners also need treatment, even if they have no symptoms. For chlamydia and gonorrhea, some states allow what’s called expedited partner therapy, where your doctor can prescribe antibiotics for your partner without seeing them in person. This is especially useful when a partner is unlikely to visit a clinic on their own. For chlamydia, the partner typically receives azithromycin or doxycycline. For gonorrhea, an oral antibiotic called cefixime can be given to partners when the standard injection isn’t feasible, though the injection remains preferred.
Why the Right Diagnosis Matters
No single antibiotic covers all STIs. Doxycycline won’t cure gonorrhea. The penicillin shot for syphilis won’t touch chlamydia. And viral STIs like herpes, HIV, and hepatitis are managed with antiviral medications, not antibiotics at all. Getting tested for the specific infection you have, rather than guessing or relying on symptoms alone, is the only way to ensure you get the right treatment. Many STIs share overlapping symptoms like discharge, burning, or no symptoms at all, which makes lab testing essential for choosing the correct antibiotic.