Most STD antibiotics cause only mild, short-lived side effects. Doxycycline can upset your stomach and make your skin burn faster in the sun; metronidazole and tinidazole react badly with alcohol; and the gonorrhea injection mainly leaves the spot sore. Most people start feeling better within a few days, but finishing the full course matters more than how you feel.
antibiotics clear them
medicine controls, doesn't cure
| Item | Value |
|---|---|
| Bacterial & parasitic (chlamydia, gonorrhea, syphilis, trich) | curable — antibiotics clear them |
| Viral (herpes, HIV, hepatitis B, HPV) | managed — medicine controls, doesn't cure |
What to expect when you start STI treatment
Treatment is usually less of an ordeal than the anxiety leading up to it. For a curable bacterial or parasitic STI, you're looking at either a short course of pills or a single dose given on the spot — and that's often free or low-cost at a health department or Planned Parenthood. Many people never even pay for a prescription, and in much of the country your partners can be treated without their own clinic visit through expedited partner therapy, where the clinician sends medication or a prescription home for them.
Once you take the medicine, symptoms tend to ease within a few days CDC STI Guidelines, 2021. Discharge settles, burning with urination fades, and irritation calms down. That improvement is real, but it isn't proof the infection is gone. Some infections need a test-of-cure or a retest weeks to months later to confirm the bug is cleared and that you weren't reinfected. Feeling better is the start of recovery, not the finish line.
Two rules protect that recovery. Take every dose exactly as prescribed, even after symptoms vanish, and make sure your partners are treated too. Skipping either is the single most common reason an infection quietly persists or bounces straight back the moment you have sex again. Hold off on sex until you and your partners have both finished treatment and any waiting period your clinician sets — often about a week after a single-dose treatment — so you're not passing the same infection back and forth.
Drug-specific side effects and warnings
Doxycycline
Doxycycline is a workhorse antibiotic for chlamydia and several other infections, taken as a short course of pills. Its two signature side effects are stomach upset — nausea or queasiness, sometimes worse on an empty stomach — and photosensitivity, meaning your skin sunburns much faster than usual, even on a cloudy day. Take each dose with food and a full glass of water to settle your gut, stay upright for a while afterward so the pill doesn't irritate your esophagus, and cover up or use sunscreen if you'll be outside. If you want the full recovery picture for that infection, see our guide to chlamydia treatment.
Metronidazole and tinidazole
These are the standard drugs for trichomoniasis and bacterial vaginosis CDC Trichomoniasis Treatment. The detail people search before they fill the prescription: alcohol. Mixing either drug with alcohol can trigger a rough reaction — flushing, nausea, vomiting, a pounding headache — so skip alcohol entirely during treatment and for a short stretch after you finish your last dose. That includes hidden sources like cough syrups and some mouthwashes. A metallic taste in the mouth and mild stomach upset are also common and harmless.
The gonorrhea injection
Gonorrhea is now treated with a single ceftriaxone injection — and that's not a matter of convenience. Gonorrhea has grown resistant to nearly every antibiotic once used against it, which is why the shot is the only treatment still reliably recommended CDC Drug-Resistant Gonorrhea. Taking the right drug at the right dose is part of keeping it treatable for everyone. The main side effect is soreness, redness, or a small lump where the needle went in, which fades over a day or two. If you're still working out whether you need it, start with a gonorrhea test.
| Medication | Typically treats | Main side effects | Key precaution |
|---|---|---|---|
| Doxycycline (pills) | Chlamydia, others | Stomach upset, sun sensitivity | Take with food; avoid strong sun |
| Metronidazole / tinidazole (pills) | Trichomoniasis, BV | Nausea, metallic taste | No alcohol during and shortly after |
| Ceftriaxone (single injection) | Gonorrhea | Injection-site soreness | Given in clinic; complete any partner treatment |
Curable versus managed: what the antibiotic can actually do
Whether an STI can be cured comes down to what causes it. Bacterial and parasitic infections — chlamydia, gonorrhea, syphilis, and trichomoniasis — are cured with antibiotics. Viral infections — herpes, HIV, hepatitis B, and HPV — are controlled with medicine but not cured; antiviral treatment keeps them in check rather than eliminating them. This matters because antibiotics do nothing against a virus. Taking an antibiotic for herpes or HIV won't help and contributes to antibiotic resistance, the same force that already wiped out most gonorrhea treatments.
It also means there's no shortcut. No over-the-counter product or home remedy cures a bacterial or viral STI — yogurt, garlic, douching, and detoxes do nothing for the infection itself. What clears a curable STI is the specific prescription medicine matched to a real diagnosis, which starts with a test. If you haven't been tested yet, get tested before you assume what you're dealing with.
When the medicine isn't working: red flags
Most courses go smoothly, but a few signs mean you should circle back to a clinician rather than wait it out:
- Symptoms that don't improve at all within a few days, or that worsen after you've started treatment.
- Symptoms that clear and then return — often a sign of reinfection from an untreated partner rather than treatment failure.
- Severe vomiting that makes it impossible to keep oral medication down, so you're not actually absorbing the dose.
- Signs of a true allergic reaction: hives, swelling of the lips, face, or throat, or trouble breathing — these need urgent care.
- A drug-and-alcohol reaction on metronidazole or tinidazole that leaves you violently ill.
Persistent symptoms after a full, correct course aren't a reason to double down on home remedies — they're a reason to be re-evaluated, since you may need a different drug, a test for reinfection, or treatment for a second infection found at the same time.
When to see a clinician
See a clinician before starting if you've never been diagnosed — guessing wastes time and risks the wrong drug. See one during treatment for any of the red flags above. And plan a follow-up if your clinician asked for a test-of-cure or a retest, because some infections are confirmed cleared only by a later test, not by how you feel. If you're treating after a recent exposure, our guide on when to test after exposure explains why timing your retest matters.