Medication · sulfonamide trimethoprim

Supplements and Co-trimoxazole.

Every documented pair, every citation. Below: 2 documented pairs grouped by mechanism.

Co-trimoxazole, sold under the brand name Septrin, is classified under "sulfonamide trimethoprim" in the BNF.

Co-trimoxazole is an antibiotic, usually taken as a short course, and the supplement questions people ask most when given one have reassuring answers. Probiotics are fine to take alongside it and lower the chance of antibiotic-related diarrhoea: space a bacterial probiotic, most Lactobacillus or Bifidobacterium products, about two hours from your dose, while Saccharomyces boulardii, which is a yeast, can be taken at the same time. Most everyday vitamins and minerals have no significant interaction with a short antibiotic course, so a daily multivitamin, vitamin D or vitamin C is generally not a concern. The combinations that genuinely matter are listed below with their evidence, and they tend to be specific: supplements that thin the blood, serotonergic supplements stacked on certain antibiotics, and supplements that are really a prescription drug in disguise, such as red yeast rice, which contains the statin lovastatin. The sensible step in every case is to tell your pharmacist what you already take, which is free at any UK community pharmacy.

Below are the 2 documented pairs we have explicitly assessed against Co-trimoxazole in the Distil database: 1 red and 1 green. The pairs cluster around 2 mechanisms: Additive hyperkalaemia (raised potassium) and Probiotic timing with antibiotics. Every call is cited to either a clinical reference (PMID) or the British National Formulary. Anything not on this list is either still to be assessed or beyond our database scope. The checker beneath surfaces assessments by supplement, and the missing-item form at the bottom of the page routes any uncatalogued supplement into our next curation pass.

Documented interactions

Additive hyperkalaemia (raised potassium)

Red Potassium

Co-trimoxazole contains trimethoprim, which makes the body hold on to potassium by acting on the kidney in much the same way as the potassium-sparing diuretic amiloride. Adding a potassium supplement on top can push potassium to a dangerous level and affect the heart rhythm, and in older people on certain heart or blood-pressure medicines this combination has been linked to sudden death. Do not take potassium with co-trimoxazole unless your specialist has advised it and is monitoring your blood potassium closely.

PMID 8328738 · PMID 20585070 · PMID 21911446 · PMID 25359996 · BNF: Co-trimoxazole

Probiotic timing with antibiotics

Green Probiotics

These are fine to use together, and probiotics may lower the chance of antibiotic-related diarrhoea. If you take a bacterial probiotic (most Lactobacillus or Bifidobacterium products), space it about two hours away from your co-trimoxazole dose so the antibiotic does not reduce the live bacteria. Saccharomyces boulardii is a yeast rather than a bacterium, so the antibiotic does not affect it and it can be taken at the same time. The main exception is if your immune system is seriously weakened or you are critically ill in hospital, when probiotics, particularly Saccharomyces boulardii, should be checked with your doctor first.

PMID 22570464 · PMID 29257353 · PMID 20458757 · BNF: Co-trimoxazole

What this list does not say. Pairs not flagged here are not implicitly safe. They are either not yet in our database, or fall outside our inclusion scope (food-supplement interactions only; for drug-drug interactions, the BNF is authoritative). Use the checker below to surface any supplement, and submit a missing item if you take something we have not catalogued.

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For adults over 18. This tool gives evidence-graded information, not medical advice. Always discuss changes with your GP, especially if you take any medication, are pregnant, breastfeeding, or have a serious health condition.

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Distil's interactions database is reviewed and updated every quarter. We grade evidence transparently and publish our methodology, including every database change, at /about/methodology. This tool is information, not a substitute for clinical judgement. If you take medication and supplements together, your GP or pharmacist can review your full regimen against your medical history. If you want a full personalised stack reasoned against this same database, the Distil report is the next step up.