Updated January 2014


Trichomoniasis is a common sexually transmitted infection (STI) caused by a single cell protozoan, Trichomonas vaginalis.


Trichomoniasis is most often spread through unprotected vaginal intercourse (penis to vagina, vagina to penis or vagina to vagina) with an infected partner. Rarely it can be passed through unprotected anal or oral sex.

Signs & Symptoms

If symptoms do occur, they usually appear within one week after the infection, but can take up to six months. For some people, symptoms may go away and then return later. Many people, particularly men, will have no symptoms. Symptoms in men can include penile discharge, burning when urinating or after sex, and/or irritation or redness at the tip of the penis. About 50 per cent of women will have symptoms, which can include vaginal itching, pain during sex or when urinating, and/or a foul smelling grey, yellow or greenish vaginal discharge.

Diagnosis & Tests

For women, a sample of fluid from the vagina is collected for testing. A pap test may also show the infection. For men, a sample of discharge from the tip of the penis is needed to complete testing.


In rare cases, trichomoniasis can cause pelvic inflammatory disease (PID) in women, which can lead to infertility, chronic pelvic pain or ectopic pregnancy. If a pregnant woman is infected, it may cause premature delivery or low birth weight.

In men, trichomoniasis can cause infertility, discomfort after urination or ejaculation or chronic prostatitis.


The most effective treatment for trichomoniasis is an antibiotic called metronidazole (Flagyl). Some people may feel nauseated or have diarrhea when taking this medication, while others may notice a dry metallic or bitter taste in their mouth. You should not drink any alcohol (beer, wine or liquor) during treatment and for 24 hours afterwards. Alcohol and metronidazole can cause severe nausea and vomiting.

If you are pregnant or breastfeeding, talk to your health care provider before taking any medication.

Prevention/Self-care Tips

Here are a few important points to remember:

  • Take all medication as prescribed by your health care provider or clinic.
  • It is important not to have sex during treatment and for seven days after you and your sexual partner(s) have been treated. A person can get re-infected every time they have sex with an infected partner who has not been treated.
  • If you have an untreated STI like trichomoniasis, it is easier to get HIV from a person who has it or to pass HIV to another person.
  • It is possible to have more than one infection at a time, so it is important to be tested for other STIs.
  • Use condoms correctly every time you have sex to lower your chance of getting an STI, including HIV.

Information for Sexual Partners

All sexual partner(s) need treatment to prevent re-infection. Do not have sex while you and your partner are on the medication and for seven days after you both finish. If you use sex toys do not share them and follow the instructions on how to clean them properly.

More Information

Call the Sexual Health Infoline Ontario at 416-392-2437 or 1-800-668-2437

Safer sex: To reduce your risk of getting a sexually transmitted infection (STI), use a condom every time you have vaginal, anal or oral sex.