Trichomonas Infection

Trichomonas infection is a sexually transmitted disease. It is not normally serious but symptoms can be unpleasant. A course of medicines called antibiotics usually clears the infection.

What is trichomonas and how common is it?

Trichomonas is a protozoan, which is a tiny germ, similar to bacteria. It can infect the genital area. That is, the vagina and urethra in women, and the urethra and sometimes the prostate gland in men. The infection does not usually go further into the body and so does not tend to be as serious as other sexually transmitted infections (STIs).

Infection with trichomonas is uncommon. There are around 6,000 cases diagnosed each year in the UK.

What are the symptoms of a trichomonas infection?


  • A vaginal discharge is common. This is typically greeny-yellow, and may be 'frothy'. The discharge usually has an unpleasant or fishy smell.
  • Your vagina and vulva may be itchy and uncomfortable. The irritation may extend into the groin. Sex may be painful.
  • It may be sore when you pass urine.
  • No symptoms occur in up to half of infected women. However, you can still pass on the infection even if you have no symptoms.


  • Discharge from the penis is common.
  • It may be sore when you pass urine.
  • You may pass urine frequently (due to irritation inside the penis).
  • No symptoms occur in up to half of infected men. However, you can still pass on the infection even if you have no symptoms.

How does trichomonas infection occur?

Trichomonas infection is usually passed on by having sex with an infected person. As no symptoms may occur in both men and women who are infected, you can pass on the infection without realising it.

What are the possible complications with trichomonas infection?

  • Pregnancy. If you have untreated trichomonas infection during pregnancy, you have an increased risk of having an early labour and a baby with a low birth weight.
  • In men, trichomonas infection can, rarely, cause an unpleasant infection of the prostate gland (called  prostatitis).
  • HIV. If you have untreated trichomonas infection, you have an increased risk of developing HIV infection if you have sex with someone who is infected with HIV.

How is trichomonas infection diagnosed?

It is important to get the correct diagnosis, as the same symptoms can be caused by a number of different infections:

  • A doctor or nurse may take a sample (swab) of the discharge from the vagina or penis. This is sent to the laboratory to be tested.
  • Trichomonas is sometimes seen by chance when a smear test is done in women.
  • A sample of urine from men may also show the infection.

What is the treatment for trichomonas infection?

An antibiotic medicine called metronidazole is the common treatment. More than 9 in 10 infections clear with a short course of metronidazole tablets. Treatment is usually straightforward. Read the leaflet that comes with the tablets for a full list of possible side-effects and cautions. However, the main points to note about metronidazole include:

  • The usual dose is 400 mg twice a day for 5-7 days. A single dose of 2 grams is an alternative, although this may be less effective and may cause more side-effects.
  • Some people feel sick, and may be sick (vomit) when they take metronidazole. This is less likely to occur if you take the tablets straight after food.
  • A metallic taste is also a common side-effect.
  • Do not drink any alcohol while taking metronidazole, and for at least 48 hours after stopping treatment. The interaction with alcohol can cause you to be sick and can cause other problems.
  • Breast-feeding: metronidazole can get into breast milk, but is not thought to affect breast-fed babies. However, to play safe, the standard 7-day course with the lower dose is preferred so that a baby does not get a large dose. If it is essential to use the large 2-gram single dose then it should be taken after the last breast-feed of the evening, at the start of the overnight breast-feeding break, to limit exposure to the baby.

Tinidazole is an alternative antibiotic medicine that is sometimes used.

If you do not take treatment, in some cases the infection clears away by itself. However, this may take several weeks, and there is no way of predicting if it will clear or not. Therefore, treatment is usually advised in all cases.

Does my sexual partner need treating?

Yes. Even if they do not have symptoms. You and your partner should be treated at the same time. You should not have sex until you have finished treatment, and symptoms have gone.

Some other points about trichomonas infection

  • After you are treated, you may get the infection back if your sexual partner was not treated, or if you have sex with a new partner who has the infection.
  • Other STIs are more common in people with trichomonas infection. You (and your partner) may be advised to be tested for other infections.

If you suspect that you have trichomonas, or any other a sexually transmitted disease, then see your GP or contact your local genitourinary medicine (GUM) clinic. You can go to the local GUM clinic without a referral from your GP. The BASHH website (see link below) includes information about where you can find your local clinic.