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Buy trimethoprim safely, securely and easily in a few simple steps. Start a consultation today to check your eligibility with a prescribing clinician, at no cost to you.

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This content is intended for UK audiences only

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Manufactured by various MHRA-approved generic manufacturers


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Dispensed in the UK
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Updated on 26 Mar 2024

What to do if you missed your trimethoprim dose

Report suspected side effects or adverse reactions to the Medicines and Healthcare Products Regulatory Agency (MHRA) using the Yellow Card Reporting system that covers medicines, vaccines, e-cigarettes and medical device incidents.

Learn more about reporting side effects

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About trimethoprim

Trimethoprim is an antibacterial agent used for the treatment of bacterial infections, cystitis and urinary tract infections (UTIs). Trimethoprim stops bacterial dihydrofolate reductase, an enzyme that helps with the formation of tetrahydrofolic acid, preventing the production of bacterial DNA. Trimethoprim may be used alone or with sulfamethoxazole (co-trimoxazole) for the treatment and/or prophylaxis of UTIs.

NowPatient offers trimethoprim as a treatment for cystitis only, following an online consultation with a prescribing clinician.

Key facts of trimethoprim

  • Trimethoprim is an antimicrobial used to treat bacterial infections, cystitis and UTIs
  • Trimethoprim can be taken up to 3 days
  • Trimethoprim has some common side effects which include nausea and vomiting
  • It can be dangerous if you take trimethoprim with certain medications. If you’re not sure if it is safe, discuss this with the prescribing clinician

Who is trimethoprim not suitable for?

Trimethoprim may not be suitable for some people. To make sure it’s safe for you, speak to the prescribing clinician before taking trimethoprim if you:

  • Are allergic to trimethoprim
  • Have liver or kidney disease
  • Have high blood potassium levels (hyperkalemia)
  • Have galactose intolerance, glucose-galactose malabsorption, or total lactase deficiency
  • Have anemia or folate deficiency (low folic acid in your blood)
  • Have porphyria or any other blood disorder
  • Are pregnant or trying to get pregnant

How and where to get trimethoprim?

Trimethoprim is only available with a prescription. It is not available over the counter at a pharmacy.

NowPatient does not allow customers to buy trimethoprim directly. Our service is certified, safe and effective, and we only ever treat conditions. If you book a consultation with a prescribing clinician for the treatment of cystitis, you can discuss if trimethoprim is a suitable treatment option for you.

At the end of the consultation, the clinician will decide if a treatment plan is suitable for you. If it is, the clinician will issue you with a prescription which can then be ordered, paid for and delivered directly to your chosen address by NowPatient.

Dosage and strength for trimethoprim for cystitis

Trimethoprim is available in tablet form when used for cystitis. It is available in strengths ranging from 100 mg to 200 mg.

Information about how to take trimethoprim tablets for cystitis

Trimethoprim 200mg tablets should be taken twice daily (every 12 hours) until the prescribed course is complete. It is normally a 3-day course for uncomplicated cystitis, but can be prescribed as a 7-day course.

If you have blood in your urine, have back pain, fever, chills, vomiting, or have had cystitis more than three times in one year you should see your GP as soon as possible.

What happens if you take too much trimethoprim?

If you take more than prescribed, then it can lead to some unpleasant side effects. You should talk to your doctor or reach out to one of our prescribing clinicians, if you have taken too much trimethoprim and you experience any of the following side effects:

What are the side effects of trimethoprim?

Side effects of trimethoprim are split into common and serious.

Common side effects include:

  • Nausea, vomiting, diarrhoea, and skin rash

If you experience any serious adverse effects, you should contact NHS 111.

If you experience a serious allergic reaction with the signs shown below you should contact emergency services on 999.

  • Your lips, mouth, throat or tongue suddenly become swollen
  • You’re breathing very fast or struggling to breathe (you may become very wheezy or feel like you’re choking or gasping for air)
  • Your throat feels tight or you’re struggling to swallow
  • Your skin, tongue or lips turn blue, grey or pale (if you have black or brown skin, this may be easier to see on the palms of your hands or soles of your feet)
  • You suddenly become very confused, drowsy or dizzy
  • Someone faints and cannot be woken up

Always report adverse effects to the MHRA yellow card reporting system. You can read more about this here How and where do I report side effects of my medication? – NowPatient

Information about taking trimethoprim at the same time as other medications or herbal supplements

There is not enough evidence to suggest there are any drug interactions between herbal supplements and trimethoprim. In any event, you should let your prescribing clinician know if you are taking any herbal supplements or other prescription drugs, such as:

  • ACE inhibitors
  • Azathioprine
  • Cyclosporin
  • Digoxin
  • Methotrexate
  • Phenytoin
  • Repaglinide
  • Rifampicin
  • Warfarin, heparin

Why might trimethoprim not work for cystitis?

Trimethoprim may not work for you. A common reason may include aquired trimethoprim resistance.

Can trimethoprim taken for cystitis be taken long term?

Taking a 3-day course of trimethoprim should clear most bladder and urinary tract infections. If your symptoms have not cleared once you have completed your course of trimethoprim, speak to your doctor for medical advice.

Is there a herbal trimethoprim?

No. Herbal trimethoprim does not exist. If you have been marketed such a formulation, it may be fake.

Can women use trimethoprim?

Women can take trimethoprim for the treatment of cystitis. However, trimethoprim should not be used during pregnancy and only under the guidance of your doctor when breastfeeding.

Should I avoid any particular food or drink when taking trimethoprim?

You can eat and drink normally when taking trimethoprim.

What lifestyle changes can I make to help me with cystitis?

You may modify your lifestyle in a number of ways, and this may have a positive impact on your cystitis. Drink plenty of water when suffering from cystitis to flush bacteria through your system and to help keep hydrated to prevent cystitis from recurring. Also, wipe from front to back when you go to the toilet, to prevent infection.

Alternatives to trimethoprim

Alternatives for the treatment of cystitis include nitrofurantoin, quinolones, or amoxicillin.


Medical Disclaimer

NowPatient has taken all reasonable steps to ensure that all material is factually accurate, complete, and current. However, the knowledge and experience of a qualified healthcare professional should always be sought after instead of using the information on this page. Before taking any drug, you should always speak to your doctor or another qualified healthcare provider.

The information provided here about medications is subject to change and is not meant to include all uses, precautions, warnings, directions, drug interactions, allergic reactions, or negative effects. The absence of warnings or other information for a particular medication does not imply that the medication or medication combination is appropriate for all patients or for all possible purposes.

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