Sounds like 'tri-meth-o-prim'

Easy-to-read medicine information about trimethoprim – what it is, how to take trimethoprim safely and possible side effects.

Type of medicine Also called
  • Antibiotic (to treat infection)
  • TMP Tablet®

What is trimethoprim?

  • Trimethoprim is an antibiotic that is used to treat infections of the urinary tract, such as bladder infections. 
  • It works by killing or stopping the growth of the bugs that cause the infection.
  • In patients who get urinary tract infections often, trimethoprim can be used to prevent such infections.


  • Always take your trimethoprim exactly as your doctor has told you. The pharmacy label on your medicine will tell you how much trimethoprim to take, how often to take it, and any special instructions.

How to take trimethoprim

  • You can take trimethoprim with or without food. If you get stomach upset, try taking it with food.
  • Keep taking trimethoprim until you finish all the tablets, for as long as your doctor or pharmacist tells you to.
  • Do not stop taking trimethoprim, even if you feel better after a few days, unless your doctor tells you to.
  • If you forget to take trimethoprim, take it as soon as you remember.
  • But, if it is nearly time for your next tablet, just take the next tablet at the right time. Do not take double the amount of tablets.

Possible side effects

Like all medicines, trimethoprim can cause unwanted side effects, although not everyone gets them. Often unwanted side effects improve as your body adjusts to the new medicine

Side effects What should I do?
  • Headache
  • Feeling sick or nausea
  • Decreased appetite
  • Difficulty sleeping
  • These are quite common when you first start taking trimethoprim, and usually go away with time.
  • Tell your doctor if troublesome.
  • Signs of problems with your liver such as yellowing of the skin or eyes, pain in the abdomen
  • Tell your doctor immediately or ring HealthLine
  • Signs of an allergic reaction such as skin rashes, redness, itching, blisters on the skin
  • Tell your doctor immediately or ring HealthLine


Trimethoprim may interact with a few medications and herbal supplements so check with your doctor or pharmacist before starting trimethoprim or before starting any new medicines.

Learn More

Medsafe Consumer Information Sheet   TMP Tablet

New Zealand Formulary Patient Information: trimethoprim

Credits: Sandra Ponen, Pharmacist. Reviewed By: Dr Janine Bycroft, GP, Health Navigator NZ