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Why Take Trimethoprim at Night?

Trimethoprim is a popular antibiotic for treating UTIs and cystitis. It inhibits bacterial growth and often relieves symptoms within a few days.

If you’ve been prescribed trimethoprim for a urinary tract infection (UTI) or cystitis, you will have been told to take it at night. What difference does it really make? What would happen if you were to take it during the day? It’s important to understand more about why trimethoprim should be taken at night so you can follow the instructions your doctor has given you.

The Importance Of Timing

Timing is always important when it comes to taking medication to prevent accidental overdoses and to ensure that the medication is able to work in the most efficient way, and trimethoprim is no exception. What is more unusual with this antibiotic, however, is that it should be taken at night, and there are several reasons for this:

  • Maximum Absorption: Our circadian rhythm can have a big impact on how well medication is absorbed into our body. With trimethoprim, the best time to take it for the maximum possible absorption and therefore the fastest recovery is at night – this ensures enough trimethoprim gets to the urinary tract.
  • Patient Convenience: In simple terms, taking a pill just before you go to sleep is a convenient way for most people to handle their prescriptions. The routine makes it easy to remember, and no matter what else you might be doing or how busy you are, you won’t run the risk of accidentally skipping a dose, which is unwise.
  • Reduced Side Effects: Some people will experience mild side effects when taking trimethoprim including dizziness and nausea. If you take trimethoprim at night, these side effects will be reduced because you’ll be asleep for most of the time the medication is in your system.

The Science Behind Nighttime Dosage

Studies have shown that the way the human body works during the day is different from how it works at night, with different processes taking place and different metabolic rates being utilised. When taking trimethoprim at night, you’re able to make the most of these differences and ensure that you’re optimising trimethoprim’s effectiveness.

Benefits And Considerations Of Taking It At Bedtime

One benefit of taking trimethoprim at bedtime is that you’re more likely to remember to take your pills, meaning you’ll get through your course of antibiotics correctly and your UTI will be treated effectively. Plus, as mentioned above, nighttime is when trimethoprim can work most effectively.

Contradictions And Exceptions

While taking trimethoprim at bedtime is usually recommended, there will always be exceptions, and certain medical conditions or other factors such as other medication might mean daytime is a better option. Always follow the advice of your healthcare provider, as they will consider your specific situation when prescribing medication.


There are good reasons for taking trimethoprim at night, including better absorption, reduced side effects, and more convenience. However, it’s always best to follow your doctor’s instructions, as they will have taken other factors into consideration before determining the best way to take trimethoprim in your specific situation.

Authored & Reviewed By

Mohamed Imran Lakhi

MPharm - Lead Pharmacist
Imran Lakhi is the superintendent pharmacist and founder at Prescription Doctor. He has been at the core of our team.

Published on: 11/09/2023 Reviewed on: 01/11/2023
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