Key Takeaways
- Trichomoniasis is caused by the parasite Trichomonas vaginalis and is the most common nonviral sexually transmitted infection, with about 2.6 million U.S. cases.[1]
- Most people, 70 to 85 percent, have minimal or no symptoms, which is why it spreads so easily.[1]
- Treatment is a nitroimidazole antibiotic: metronidazole 500 mg twice daily for 7 days in women, metronidazole 2 g once in men, or tinidazole 2 g once as an alternative.[1]
- All sex partners must be treated at the same time, and sex should stop until everyone is treated and symptoms clear, or reinfection is almost guaranteed.[1]
- Women should be retested about 3 months after treatment because reinfection is common.[1]
- Infection raises the risk of HIV acquisition and, in pregnancy, preterm birth, which is why prompt treatment matters.[1]
Trichomoniasis, often shortened to trich, is the sexually transmitted infection most people have heard of least. It is the most common nonviral STI on Earth, yet because most people who carry it have no symptoms, it passes quietly between partners and is often picked up only because someone was tested, not because someone felt sick. The good news is that it is curable with a short course of a well-established antibiotic. The catch is that the cure only sticks if partners are treated together.
This guide covers what trichomoniasis is, how it is detected, the exact treatment regimens, and why partner treatment is not an optional add-on but the difference between a cure and a reinfection. Every clinical claim is cited to a primary source.
What Is Trichomoniasis?
Trichomoniasis is a sexually transmitted infection caused by a single-celled parasite called Trichomonas vaginalis.[1] It is the most prevalent nonviral STI worldwide and affects an estimated 2.6 million people in the United States.[1] In women it infects the vagina, urethra, and nearby glands; in men it most often lives in the urethra.
Symptoms: Often Silent
The defining fact about trichomoniasis is that most people with it have few or no symptoms, roughly 70 to 85 percent.[1] When symptoms do appear in women, they include a diffuse, often smelly, yellow-green vaginal discharge and vulvar irritation or itching.[1] In men, symptoms are typically urethritis, a burning on urination, and less often prostatitis or epididymitis, but most men are asymptomatic.[1]
How It Spreads
Trichomoniasis passes between partners during penile-vaginal sex, and among women who have sex with women through infected vaginal fluids.[1] It is not spread through casual contact, toilet seats, or sharing food. Because the infection is often silent and can last months to years untreated, an untreated partner is the single most common source of reinfection.[1]
How It Is Diagnosed
Testing has improved substantially. The gold standard is now a nucleic acid amplification test, or NAAT, which detects the parasite's genetic material with sensitivity of roughly 95 to 100 percent.[1] The older method, examining a sample under a microscope called a wet mount, is faster and cheaper but misses over a third of infections, with sensitivity of only 44 to 68 percent.[1] For an accurate answer, NAAT is the test to ask for.
Trichomoniasis vs BV vs Yeast
Vaginal discharge has several causes, and the distinction changes treatment completely. Trichomoniasis, bacterial vaginosis, and a yeast infection are the three most common, and they are easy to confuse without testing.
| Feature | Trichomoniasis | Bacterial vaginosis | Yeast infection |
|---|---|---|---|
| Cause | Parasite (T. vaginalis)[1] | Bacterial overgrowth | Fungus (Candida) |
| Discharge | Yellow-green, frothy, smelly[1] | Thin, gray, fishy odor | Thick, white, cottage-cheese, no odor |
| Itch | Vulvar irritation, sometimes | Mild or absent | Intense itching |
| Treatment | Metronidazole or tinidazole[1] | Metronidazole or clindamycin | Antifungal |
Treatment: Metronidazole and Tinidazole
Trichomoniasis is cured with a class of antibiotics called nitroimidazoles, and these are the only drugs proven to work.[1] The specific regimen depends on sex and circumstances.
| Person | Recommended regimen | Cure rate |
|---|---|---|
| Women | Metronidazole 500 mg by mouth, twice daily for 7 days | about 84 to 98%[1] |
| Men | Metronidazole 2 g by mouth, single dose | about 84 to 98%[1] |
| Either (alternative) | Tinidazole 2 g by mouth, single dose | about 92 to 100%[1] |
| Women with HIV | Metronidazole 500 mg by mouth, twice daily for 7 days | [1] |
The 7-day course of metronidazole is now recommended for women over the old single-dose approach, because it is more effective, particularly for symptomatic women.[1] A newer single-dose option, secnidazole 2 g, is also approved and effective.[3] Topical metronidazole gel is not recommended because it does not reach therapeutic levels where the parasite hides.[1]
Treating Partners Is Not Optional
This is the step that determines whether treatment actually sticks. Because most infections are silent and most repeat infections come from an untreated partner, all current sex partners should be treated at the same time, and sex should stop until everyone is treated and symptoms have resolved.[1] Testing for other STIs, including HIV, syphilis, gonorrhea, and chlamydia, should happen at the same time.[1]
What If It Comes Back?
Reinfection from an untreated partner is the most common reason trichomoniasis returns, but true treatment failure also happens, with metronidazole resistance in roughly 4 to 10 percent of cases.[1][2] When infection persists without reexposure, retreatment uses higher-dose or longer nitroimidazole courses, and drug-resistance testing can guide care.[1]
| Situation | Retreatment regimen |
|---|---|
| Reexposed to an untreated partner | Repeat the same metronidazole regimen[1] |
| Not reexposed, persistent infection | Metronidazole or tinidazole 2 g once daily for 7 days[1] |
| Documented resistance | Metronidazole or tinidazole 2 g daily for 7 days, with resistance testing[1] |
Complications
Untreated trichomoniasis is not benign. It raises the risk of acquiring HIV by about 1.5 fold, and in women with HIV it increases viral shedding and the risk of pelvic inflammatory disease.[1] During pregnancy it is linked to premature rupture of membranes, preterm birth, and small-for-gestational-age infants.[1] These are the reasons prompt diagnosis and treatment matter even in people without symptoms.
A Note on Pregnancy
Trichomoniasis during pregnancy is associated with adverse pregnancy outcomes, and symptomatic pregnant people should be tested and treated.[1] Metronidazole is used in pregnancy at low fetal risk, while tinidazole is avoided.[1] This guide's treatment discussion is for adults who are not pregnant, and any infection during pregnancy should be managed by the obstetric team rather than through general telehealth care.
Prevention
Prevention is straightforward and familiar. Consistent and correct condom use reduces transmission, douching should be avoided because it can raise the risk of vaginal infections, and partners should be treated together so the infection does not bounce back.[1] Because most infections are silent, the habit that matters most is testing when there is any new partner or any symptom.
When to See a Doctor
You have any vaginal discharge, itching, burning on urination, or you have had a partner diagnosed with an STI. Because most infections are silent, testing is reasonable after any new partner even without symptoms.[1]
Frequently Asked Questions
Yes. Men can carry and transmit Trichomonas vaginalis, usually in the urethra, and most have no symptoms. That is why treating male partners is essential to cure.[1]
No. It requires antibiotic treatment to cure, and left untreated it can last months to years and keep spreading.[1]
No. Trichomoniasis is caused by a parasite and is sexually transmitted, while bacterial vaginosis is a bacterial imbalance not classified as an STI. They look different and testing distinguishes them.[1]
Either 7 days of metronidazole taken twice daily, or a single dose of metronidazole or tinidazole, depending on the regimen prescribed.[1]
Yes. All sex partners should be treated at the same time, and sex should stop until everyone is treated and symptoms clear. Skipping this invites reinfection.[1]
A nucleic acid amplification test, or NAAT, with sensitivity around 95 to 100 percent. A microscope wet mount is faster but misses over a third of infections.[1]
Untreated, it raises the risk of HIV acquisition, pelvic inflammatory disease, and, in pregnancy, preterm birth. It is curable, which is why prompt treatment matters.[1]
Yes, reinfection is common, most often from an untreated partner. Women are retested about 3 months after treatment for this reason.[1]
Yes, the discharge can be malodorous, often described alongside a yellow-green, frothy appearance. Testing, not smell, is the reliable way to tell it from other infections.[1]
Symptomatic pregnant people are tested and treated with metronidazole, while tinidazole is avoided. Pregnancy care is managed by the obstetric team.[1]
No. The cure requires prescription antibiotics such as metronidazole or tinidazole, so a clinician must confirm the diagnosis and prescribe.[1]
References
- Centers for Disease Control and Prevention. Sexually Transmitted Infections Treatment Guidelines, 2021: Trichomoniasis. cdc.gov
- Jenks JD, Plasner S. Trichomoniasis. StatPearls. Updated 2026. PubMed PMID 30521247
- Muzny CA, Van Gerwen OT, Legendre D. Secnidazole: a treatment for trichomoniasis in adolescents and adults. Expert Review of Anti-infective Therapy. 2022;20(8):1067-1076. doi:10.1080/14787210.2022.2080656