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Side effects of Trimethoprim tablets and how to buy in the UK

  • Prescription treatment for cystitis bacterial infections
  • 200 mg prescription medication to target bacteria
  • Low risk treatment for cystitis
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Antibiotic tablets used to treat cystitis in women and men, Trimethoprim comes in both 100mg and 200mg dosages to alleviate symptoms of the urinary tract infection (UTI) within days and clear the infection within a week.

With medication in the UK, you must obtain a prescription that we provide after you have completed a quick consultation. Once your symptoms and medical history has been checked, our doctors can issue your prescription and you can receive your medication the next working day free of charge.

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How to buy Trimethoprim online?

At OnlineClinic, you can order Trimethoprim 100mg or 200mg pills depending on your preference combined with the doctor's recommendation based on your symptoms. Trimethoprim 100mg is taken once daily whilst 200mg pills are taken twice daily. It's important to always complete your course of antibiotics to ensure the infection has cleared. Starting your medication quickly can stop symptoms from worsening, with many finding significant relief within just three days of beginning the course, so we offer free next day delivery with any dosage option.

To buy any medication that has gone through medical trials in the UK, you must have a prescription certified by a UK doctor to prove it is suitable and safe for you to use. OnlineClinic provide this in the form of a free online consultation based on secure medical questions that is reviewed by one of our team of doctors. When it is clear that the infection is cystitis, you want to get effective treatment quickly, so if you complete your order before 4pm you will get Trimethoprim delivered the very next day. All packages are discreet meaning you can get your treatment delivered wherever you need with complete confidentiality.

What is Trimethoprim?

Trimethoprim is a course of antibiotic tablets designed to alleviate the symptoms of cystitis to eventually clear the infection completely. Many people find symptoms significantly lessening within three days and clearing completely by the end of the course. Trimethoprim can be used for many bacterial infections but it's most popular use is for UTIs, in particular cystitis.

Short facts about Trimethoprim
How to take

One Trimethoprim tablet should be taken a day, ideally in the evening, with or without food. This is the standard dosage for UTIs, it may vary for other conditions, or severity.

How it works

Trimethoprim works by significantly reducing the production of folic acid so the bacteria causing the symptoms of cystitis can't spread. This allows your immune system to combat the infection.


Trimethoprim is clinically proven to relieve symptoms within days. Many women find the infection clearing entirely within one week.


Available in both 100mg and 200mg pills. 100mg is recommended as a preventative treatment for daily use, whilst 200mg is a 7-day course.

Side effects

Side effects of Trimethoprim are usually temporary and very manageable. These only occur for the small percentage of women and can include nausea or vomiting and headaches.

How does Trimethoprim work?

Being an antibiotic, Trimethoprim can treat and cure bacterial infections such as cystitis. It works by hindering the production of folic acid (folate) so the bacteria cannot replicate its DNA and multiply. By stopping this progress, Trimethoprim halts the spread of infection, allowing your immune system to take over, killing the bacteria.

How to take Trimethoprim?

Trimethoprim is simple to take, although it does vary depending on the dosage you have been advised, which will be detailed to you by a medical professional. This is based on the severity of the symptoms.

  • All tablets to be taken with water, with or without food
  • For UTIs, the standard dose is usually once a day in the evening

If you forget a pill, take it as soon as you remember unless it is near to your next dose. If this is the case, miss completely and continue to finish the dosage. Never take a double dose to make up for a missed pill.


Trimethoprim comes in 100mg and 200mg dosages. 100mg is the recommended dose, especially for UTIs. In some circumstances, you may be offered 200mg, which is taken in a different way to above. When buying online, your doctor at OnlineClinic will advise you on how to take, just the same as a face-to-face appointment.

Side effects and precautions

Side effects of any clinical medication are experienced by the minority and as Trimethoprim is taken as a set course of antibiotics and not a continual treatment, if you so experience side effects, these are usually temporary and disappear once you've finished the medication. Side effects of Trimethoprim are also often very mild and far more manageable than the symptoms of cystitis as well. Some side effects include nausea or vomiting, headache, rash and itching. There are more severe side effect symptoms to also make note of in the patient leaflet at the bottom of this page.

Precautions to be aware of whilst taking Trimethoprim include:

  • If you have a folate deficiency
  • If you have an impaired or hepatic function
  • If you have liver or kidney disease
  • If you are diabetic
  • If you have a blood disorder
  • If you have a mineral imbalance
  • You should not use Trimethoprim if you are pregnant
  • Consult your doctor before taking when breastfeeding
  • Stop taking the medication if you have symptoms of an allergic reaction

Before taking any prescription medication, you must read the leaflet fully and complete the consultation including your medical history and current medication you are taking.

Treatment Information

Treatment Information
Product Name: Trimethoprim
Active Ingredient(s): Sulfamethoxazole
Manufacturer: Crescent Pharma
Administration: Oral
Presentation: Tablets
Available Dosage: 100 mg, 200 mg
Exemption: Subject to medical prescription
Application: Women over 18 with the symptoms of cystitis
Posology: Take 1 tablet twice a day for up to 14 days
Description: Trimethoprim is an antibiotic that is used as an effective treatment for the bladder infection cystitis.
Drug class: Sulfonamides and folic acid inhibitors
Alcohol consumption: No influence
When breastfeeding: Caution is recommended, ask your doctor
When pregnant: Caution is recommended, ask your doctor
Download Trimethoprim - Patient Information Leaflet
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Current reviews for the treatment Trimethoprim

Rated with 4.9/5 based on 61 Independent customer reviews on Feefo (See all OnlineClinic reviews).

  • Outstanding

    Product ReviewSuffer from uti constantly this 100mg is a presentivie measure works perfect

    Service Review:Fantastic service , fast delivery will use again

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    Product ReviewHad an excellent effect.

    Service Review:Very prompt service.

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    Product ReviewNotice the effect within 24 hours, cleared up within 48

    Service Review:Extremely easy to use, prompt delivery, thank you

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    Product ReviewHave used this medication before which works well for me

    Service Review:Used online clinic for the first time and was very pleased with their...

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    Product ReviewExcellent professional service, which gave me confidence in ordering the...

    Service Review:Excellent professional service, which gave me confidence in ordering the...