Warders Medical Centre

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Health Information



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

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

Trichomonas is actually the most common curable STI in the world. However, it is thought that many cases are still not recognised and are not diagnosed.


  • 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 your groin. Sex may be painful.
  • You may have pain in the lower part of your tummy (abdomen).
  • It may be sore when you pass urine.
  • No symptoms occur in some 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 most infected men. However, you can still pass on the infection even if you have no symptoms.

Trichomonas infection is usually passed on by having sex (intercourse) 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.

  • 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 (intercourse) with someone who is infected with HIV.

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

  • A sample (swab) of the discharge from your vagina or penis is sent to the laboratory to be tested. This may be taken by a healthcare professional, or they may show you how to take one yourself.
  • 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.

An antibiotic medicine called metronidazole is the common treatment. You and your partner should be given treatment at the same time and you should avoid having sex (intercourse) for at least one week after receiving your treatment.

Most people with this infection 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:

  • This is usually given as a tablet twice a day for 5-7 days or a higher dose as a single dose.
  • 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 seven-day course with the lower dose is preferred so that a baby does not receive a large dose. If it is essential to use the large 2-gram single dose then breast-feeding should be discontinued for 12-24 hours after taking it.

Tinidazole is an alternative antibiotic medicine that is sometimes used. This can not be taken if you are pregnant. Breast-feeding should be avoided when taking tinidazole and also for three days after stopping it.

Yes. Even if they do not have symptoms. You and your partner should be treated at the same time.

  • 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 this 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 STI then contact your local genitourinary medicine (GUM) clinic or see your GP. You can go to the local GUM clinic without a referral from your GP. You can ring the local hospital or health authority and ask where the nearest clinic is. The FPA and BASHH websites below also include information about where you can find your local clinic.

Further help & information

Sexual Health Line England

Tel: 0300 123 7123


23-28 Penn Street, London, N1 5DL

Further reading & references

Disclaimer: This article is for information only and should not be used for the diagnosis or treatment of medical conditions. EMIS has used all reasonable care in compiling the information but makes no warranty as to its accuracy. Consult a doctor or other healthcare professional for diagnosis and treatment of medical conditions. For details see our conditions.

Original Author:
Dr Tim Kenny
Current Version:
Dr Louise Newson
Peer Reviewer:
Dr Hayley Willacy
Document ID:
4352 (v40)
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