Buy trimethoprim online to help treat cystitis

  • First-choice antibiotic for cystitis and other UTIs
  • Short 3-day course
  • Available from £13.95 + prescription fees and delivery costs

Our prices

Strength Quantity Price Stock
200mg6 tablets£13.95Out of Stock
Prices exclude a prescription fee. This treatment requires a quick online consultation,
which a doctor will review to determine if a prescription is appropriate.

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Dr Samantha Miller

Reviewed by Dr Samantha Miller MB ChB
(2017, University of Glasgow)
GMC number: 7561464

Information last reviewed 20/04/2021


What is trimethoprim?

Trimethoprim is an antibiotic. It is primarily used to treat cystitis. Cystitis is a bacterial infection of the bladder. For this reason, cystitis is often referred to as a ‘UTI’ (urinary tract infection). Occasionally, trimethoprim may be prescribed to treat other bacterial infections i.e. chest infections.

How does trimethoprim work?

Bacteria need folate to grow and survive. Trimethoprim works by stopping the production of folic acid by bacteria. This prevents the bacteria from being able to grow and spread.

How long does it take for trimethoprim to work?

Trimethoprim will usually make you feel better within a few days. However, like all antibiotics, it is vital that you complete the full course prescribed to you, even if you feel better. This helps to prevent the bacteria from developing resistance to the antibiotic, which would make it much harder to treat. If you’ve finished your course of antibiotics and you’re not feeling any better, you should see your GP as they may need to extend the course or explore alternative treatments. 

Trimethoprim summary


200mg, taken twice daily for acute infections

Type of medicine Diaminopyrimidine antibiotic

Blocks the production and use of important chemicals in bacteria, preventing growth and reproduction

Available Size

6 tablets

Available Strengths


Active Ingredient



From £2.32 per tablet

Side Effects

Can include hyperkalaemia, headache, skin rashes, hives, thrush, nausea, vomiting, diarrhoea


Active ingredients

The active ingredient in trimethoprim tablets is trimethoprim.

Inactive ingredients

The inactive ingredients in trimethoprim are colloidal silicon dioxide, lactose, macrogol, magnesium stearate, povidone, sodium starch glycollate, stearic acid and E460. 

Please note: different manufacturers of generic trimethoprim may use different inactive ingredients to those listed above.


How to take trimethoprim

Always take trimethoprim as instructed. Your doctor will tell you how many tablets to take and when they need to be taken. You should swallow the tablets with a glass of water at roughly the same time each day. 

If you realise that you have taken more trimethoprim than you should, you must contact a doctor immediately. If you forget to take a dose, you should take it as soon as possible. However, if it is very close to your next dose, you should skip the missed dose and then take your next dose at the usual time. Never take a double dose to make up for a missed one.

Trimethoprim dosage

The typical dose of trimethoprim for the treatment of uncomplicated mild cystitis in women is 200 mg twice daily for 3 days. If you are male, have severe symptoms, or have chronic cystitis (recurrent or persistent bladder irritation), your doctor may prescribe a different dose. Always take the dose prescribed for you. 

When can I stop taking trimethoprim?

You can stop taking trimethoprim when you have completed the full course prescribed to you. If you are not sure how long this is, you should speak to the prescribing doctor. Do not stop taking trimethoprim just because you feel better.

If you experience severe side effects from trimethoprim, such as an allergic reaction, you should stop taking trimethoprim and seek urgent medical attention. 

Do I need to finish the course of trimethoprim even if my symptoms have resolved?

You should always finish the course of antibiotics prescribed, even if you feel better after a few days. This is vital in preventing bacteria from developing antibiotic resistance. Antibiotic resistance can make infections much harder to treat, which could lead to serious illness.

What if I take too many trimethoprim tablets?

Always take the dose of trimethoprim prescribed by your doctor. If you take too much, contact a doctor immediately. 

Side Effects

Trimethoprim side effects

Like all medications, trimethoprim can cause side effects. The most common side effects are itchy skin, a skin rash (which occurs in up to 7% of patients) and mild gastrointestinal disturbances including nausea, vomiting and diarrhoea. These side effects are usually mild and resolve quickly after stopping the medication. If they are troubling you, speak to your doctor for advice. 

If you experience any of the following rare but severe side effects, stop taking trimethoprim and seek immediate medical attention:

  • Swelling of the face, lips, tongue or throat, or difficulty breathing
  • Chest pain, shock, fainting or collapse
  • Blistering or peeling of the skin, skin eruptions or lesions, or deep swelling of the skin known as angioedema
  • Symptoms of pancreatitis (severe upper abdominal pain, often radiating through to the back)
  • Jaundice (yellowing of the skin)

The following side effects can affect up to 1 in 10 people:

  • High levels of potassium in the blood, which may manifest as palpitations or problems with the heart rhythm
  • Nausea, vomiting or diarrhoea
  • Headache
  • Skin rashes or itchy skin
  • Anaemia, which may cause you to appear pale and feel tired
  • Sore throat or mouth ulcers
  • Thrush

The following side effects are very rare, affecting up to 1 in 10,000 people:

  • Constipation
  • Severe, watery or bloody diarrhoea
  • Cough
  • Agitation or abnormal behaviour
  • Aseptic meningitis, with symptoms such as headache, fever, stiff neck, tiredness, feeling unwell and sensitivity to bright lights
  • Kidney problems, painful urination or blood in the urine
  • Dizziness, tiredness
  • Convulsions or involuntary movements
  • Pins and needles, shakiness or tremors
  • Ringing in the ears, vertigo
  • Eye redness or pain
  • Sensitivity to sunlight
  • Low blood sugar levels, low levels of sodium in the blood, which may cause nausea, tiredness or muscle cramps
  • Anorexia
  • Depression, anxiety, sleeping difficulties, nightmares, confusion, hallucinations
  • Jaundice (yellowing of the skin and whites of the eyes), elevation of serum transaminases (an indication of liver damage), or elevation of bilirubin levels
  • Joint and muscle ache
  • Shortness of breath, wheezing, nosebleeds
  • Meningitis (stiff neck, fever, vomiting)
  • Lupus erythematosus
  • Purple discolouration of the skin
  • Fever
  • Anaemia or reduction in numbers of blood cells

How to cope with trimethoprim side effects

Trimethoprim does not usually cause side effects, but when it does, they tend to be mild and easy to manage. Mild rashes and itching can be treated by taking antihistamines, which can be purchased over the counter from a pharmacy or supermarket. 

If you experience nausea when you take your tablets, try taking them with or after a meal, and avoid rich or spicy foods. This is particularly important if your nausea leads to vomiting, as the trimethoprim may not be absorbed by the body. 

If you experience diarrhoea, make sure you stay hydrated and drink plenty of water. Speak to a doctor or pharmacist before taking any medications to treat your diarrhoea. 

Headaches resulting from dehydration can be managed by staying hydrated, and by taking over-the-counter painkillers such as paracetamol and ibuprofen if needed.


Do NOT take Trimethoprim if you:

  • Are allergic to trimethoprim or any of the other ingredients in this medication
  • Are pregnant
  • Have a blood disorder
  • Have severe kidney disease
  • Have severe liver disease

Before taking Trimethoprim, speak to your doctor if you:

  • Have kidney disease or are having dialysis treatment
  • Have a deficiency of folic acid
  • Are elderly
  • Are taking any other medications
  • Are anaemic
  • Have poorly controlled diabetes
  • Have an abnormal heart rhythm

Drug interactions

Before taking trimethoprim, tell your doctor or pharmacist if you are taking any other medications, including those purchased over the counter without a prescription. In particular, tell your doctor or pharmacist if you are taking or have recently taken any of the following:

  • Antibiotics such as rifampicin
  • Anticoagulants such as warfarin
  • Digoxin for a heart condition
  • Phenytoin for epilepsy
  • Pyrimethamine or dapsone for malaria
  • Immunosuppressant drugs used in cancer treatment (such as methotrexate) or to treat organ rejection following a transplant (such as azathioprine or ciclosporin)
  • Bone marrow depressants
  • Spironolactone for fluid build-up
  • Repaglinide for diabetes
  • Diuretics, such as water tablets furosemide or eplerenone
  • Procainamide for abnormal heart rhythm

Trimethoprim and alcohol

There is no known interaction between trimethoprim and alcohol, however, alcohol can irritate the bladder, so you should avoid drinking alcohol when you have cystitis. 

Trimethoprim and pregnancy

Trimethoprim should not be used during pregnancy as it could harm your baby. Trimethoprim works by stopping the production of folic acid which is very important for healthy development in pregnancy. Always inform the prescribing doctor if you could be pregnant before starting trimethoprim, as they can recommend a more suitable alternative. 

Trimethoprim and breastfeeding

Trimethoprim can be taken whilst breastfeeding providing that your baby is considered to be healthy by a doctor or health visitor. If you are unsure, speak to your doctor for advice before taking trimethoprim. 

Treatment Options

Trimethoprim vs nitrofurantoin

Both trimethoprim and nitrofurantoin are effective treatments for UTIs. Trimethoprim is the first-line treatment for most urinary tract infections, however, in some cases, nitrofurantoin, or other antibiotics, may be used. 

Nitrofurantoin is the first-line antibiotic to treat UTIs during pregnancy, as trimethoprim can affect the baby’s development. If you have previously tried trimethoprim, but your infection has not resolved, your doctor may suggest that you try nitrofurantoin. Your doctor may also request a urine sample. This can be used to assess the sensitivity of the bacteria to different types of antibiotics. Based on this, your pregnancy status and any other health conditions, your doctor will recommend the most suitable antibiotic for you. 

Lastly, if you have a history of kidney disease, nitrofurantoin may not be suitable for you and other antibiotics may be recommended instead. 

Treating UTIs in pregnancy

Trimethoprim should not be used during pregnancy as it can harm the baby. Instead, your doctor can recommend an alternative antibiotic for you. Nitrofurantoin or cephalexin are the first-line antibiotics to treat cystitis during pregnancy, so it is likely that you will be given one of these. The doctor may also ask for a sample of your urine, so they can work out which antibiotics the bacteria will be most sensitive to. This will help to identify the most suitable antibiotic for you and your baby. 

How to avoid UTIs

Urinary tract infections (UTIs) are caused by bacteria travelling up the urethra into the bladder. A bacteria found in the bowel, called E. coli, is usually the cause of the infection. 

UTIs can resolve on their own, but antibiotics are recommended to stop the infection from progressing. There are several steps you can take to help prevent UTIs from happening in the first place:

  • Avoid using perfumed soaps or bubble baths
  • Swap condoms or contraceptive diaphragms for other forms of contraception
  • Empty your bladder as soon as possible after sex
  • Always wipe from front to back when you go to the toilet
  • When you feel the urge, go to the toilet as soon as possible
  • Opt for breathable cotton underwear instead of synthetic materials
  • Drink plenty of water and stay well-hydrated

It is not always possible to prevent UTIs. If you notice that you experience UTIs on a regular basis, you should inform your doctor as this may be a sign of an underlying condition such as diabetes. 


Will trimethoprim stop my contraceptive from working?

Trimethoprim does not interact with any contraceptives, however, it’s advisable to avoid sexual intercourse until your infection has cleared up.

Is trimethoprim an antibiotic?

Yes, trimethoprim is an antibiotic used to treat bacterial infection.

Will trimethoprim give me thrush?

Thrush (vulvovaginal candidiasis) can occur in people taking trimethoprim. If you experience symptoms of thrush (typically a white lumpy vaginal discharge associated with vulval itching or discomfort) you should see your GP for treatment. Thrush is easily treated with antifungal medications. 

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Easy to use website. A straightforward online consultation with a quick response back. Choice of products for your condition , all with clear descriptions and prices. And an amazing super fast dispatch/delivery. I found treatment for a minor problem in 2 days, sure beats trying to get an bob urgent appointment with my local surgery! Thank you all.


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I moved 150 miles from my GP (to uni) and was unable to go home or visit a walk in for another 2 days due to being at work (12.5 hour shifts). I filled out a quick form - and 1.5 days later I had my antibiotics delivered to my door and I am on the mend. 10/10.