Thiamine + Sulfamethoxazole, Trimethoprim
Sulfamethoxazole, Trimethoprim brand names: Bactrim, Bactrim DS, Cotrim DS, Septra, Septra DS, and others.
Thiamine has a minor interaction with Sulfamethoxazole, Trimethoprim. Trimethoprim might increase blood levels of thiamine.
Read the full interaction reportThiamine and Sulfamethoxazole, Trimethoprim
Here is the interaction we found between these two, with the evidence behind it.
TRIMETHOPRIM (Proloprim)
In vitro, animal, and clinical research suggest that trimethoprim inhibits intestinal thiamine transporter ThTR-2, hepatic transporter OCT1, and renal transporters OCT2, MATE1, and MATE2, resulting in paradoxically increased thiamine plasma concentrations.
Interaction has not been documented in well-controlled studies, however, the interaction has been demonstrated in some small human studies or in controlled animal studies in conjunction with multiple case reports..
Here's something a little unusual about Bactrim (sulfamethoxazole/trimethoprim). The trimethoprim half can actually nudge your blood levels of thiamine (vitamin B1) up a bit. It does this by blocking some of the transporters that normally move thiamine in and out of your gut, liver, and kidneys, so a touch more lingers in your bloodstream.
The good news is this is rated a minor interaction, and thiamine is a water-soluble vitamin that your body handles well, so a small rise isn't something I'd lose sleep over. It doesn't make the antibiotic stronger or weaker. If you take thiamine supplements regularly or have a condition that affects your B1 levels, just mention it to your pharmacist or doctor so they can keep an eye on things.
- Vora B, Wen A, Yee SW, et al. The Effect of Trimethoprim on Thiamine Absorption: A Transporter-Mediated Drug-Nutrient Interaction. Clin Pharmacol Ther 2023;114(2):381-392.
What These Ratings Mean
Every interaction above is graded three ways — here’s the key to each label.
Clinically significant. Avoid the combination, or use only under close professional supervision.
Usually worth avoiding or managing — may need monitoring, a dose change, or timing apart.
Generally not serious. Be aware of it and mention it to your pharmacist.
- LikelyWell-controlled human studies have demonstrated the likely existence of this interaction.
- ProbableInteraction has not been documented in well-controlled studies, however, the interaction has been demonstrated in some small human studies or in controlled animal studies in conjunction with multiple case reports.
- PossibleInteraction has been documented in animal or in lab research, or the interaction has been documented in humans but is limited to case reports or conflicting clinical research exists.
- UnlikelyInteraction has been demonstrated in animal or in lab research but has been shown not to occur in humans.
- AHigh-quality meta-analysis (quantitative systematic review).
- BCase-control study.
- CConsensus.
- DAnecdotal evidence.
These ratings are for information only. Never start, stop, or otherwise change your therapy before speaking with your provider.
Thiamine Also Interacts With Other Medications
Thiamine has 2 minor known drug interactions in our database — the Sulfamethoxazole, Trimethoprim one above is one of them. If you take anything else, check it against the full list below.
Check Another of Your Medications Against Thiamine
We haven’t checked that one against Thiamine yet — ask our pharmacists directly.
Covers the 2,830 medications we’ve checked against Thiamine. Pick one to open its full report.
See Every Supplement That Interacts With Sulfamethoxazole, Trimethoprim
This page covers Thiamine only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Sulfamethoxazole, Trimethoprim page lists 174 supplements it has a documented interaction with, worst first, each one explained.
The most serious there right now: Activated Charcoal (major), American Hellebore (major), Arsenic (major), Beer (major) and Cesium (major).
By severity: 11 major · 139 moderate · 24 minor.
From our pharmacist’s overview on the Sulfamethoxazole, Trimethoprim page
“The supplement I check first with sulfamethoxazole and trimethoprim (Bactrim, Septra) is PABA, because it feeds bacteria the exact compound this antibiotic works by blocking and can cancel the treatment outright. It is one of 11 major-rated entries among 174 supplements and herbs on file here, a count that calls for genuine care.”
Reviewed by 2 · Jul 18, 2026
Taking Thiamine as Part of a Dietary Supplement Product? Check It for Interactions
We hold 3 real supplement products containing Thiamine, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Thiamine. Your product may carry other ingredients that interact with Sulfamethoxazole, Trimethoprim too, on top of Thiamine — and those would not show on this page. Find your product and we’ll check every ingredient on its label:
Where Thiamine and Sulfamethoxazole, Trimethoprim Sit Against Everything Else
Out of every supplement and medication people look up on HelloPharmacist, here is where these two land this week — and which way each has been moving.
#181 of 1,452 supplements looked up here in the last 7 days
#102 of 2,830 medications looked up here in the last 7 days
Position among everything looked up on this site, not a measure of how commonly either one is used or how important it is. A supplement can climb this list because of a news story. It counts every request to the page, automated ones included, and nothing here identifies anyone.
About Thiamine
What is Thiamine?
- Preventing or treating thiamine deficiency
- Beriberi
- Wernicke-Korsakoff syndrome (alcohol-related)
- Supporting energy and nerve function
- General B-vitamin supplementation
Thiamine (vitamin B1) is an essential nutrient your body needs to turn food into energy and to keep your nerves and heart healthy. Most people get enough from food, but supplements are clearly useful for deficiency, certain medical conditions, and people with heavy alcohol use. Talk with your pharmacist or doctor before starting it, especially if you have a chronic illness.
Other Drugs & Thiamine
Browse every other medication we’ve checked against Thiamine — both the ones with a known interaction and the ones without. Select any drug for the full detail.
No drugs match “”.
2 interactions
No interaction 2,827 drugs checked — show the list
We also checked Thiamine against these medications and found no known interaction in our sources. Open any page to confirm.
- Apixaban ›
- Amlodipine ›
- Levothyroxine ›
- Methylphenidate ›
- Warfarin ›
- Abemaciclib ›
- Ivermectin ›
- Testosterone ›
- Sertraline ›
- Acetaminophen ›
- Losartan Potassium ›
- Aspirin ›
- Rosuvastatin ›
- Metoprolol ›
- Escitalopram ›
- Clopidogrel ›
- Rivaroxaban ›
- Atorvastatin ›
- Isotretinoin ›
- Methamphetamine ›
- Tirzepatide ›
- Warfarin Sodium ›
- Ibuprofen ›
- Docusate ›
- Sumatriptan ›
- Amlodipine Besylate ›
- Valacyclovir ›
- Hydroxyurea ›
- Tadalafil ›
- Prednisone ›
- Metformin ›
- Semaglutide ›
- Amitriptyline ›
- Lisdexamfetamine ›
- Propranolol ›
- Amphetamine ›
- Methotrexate ›
- Amoxicillin ›
- Lisinopril ›
- Levothyroxine, Liothyronine ›
- Bupropion ›
- Fluoxetine ›
- Bendamustine ›
- Doxycycline ›
- Azithromycin ›
- Pregabalin ›
- Lamotrigine ›
- Gabapentin ›
- Dextroamphetamine ›
- Acyclovir ›
- Naproxen ›
- Quetiapine ›
- Clonazepam ›
- Buspirone ›
- Omeprazole ›
- Duloxetine ›
- Letrozole ›
- Acetaminophen, Aspirin, Caffeine ›
- Acetaminophen, Codeine ›
- Citalopram ›
Showing the 60 most looked-up of 2,827 medications checked with no known interaction — see the full Thiamine list.
Sources & How We Checked
Interaction details are evidence-graded and sourced from the Natural Medicines database. The medication overview comes from MedlinePlus.
- Natural Medicines (Therapeutic Research Center) — Evidence-graded clinical reference for vitamins, herbs and supplements — the basis for our interaction data.
- MedlinePlus, U.S. National Library of Medicine — NIH consumer drug information, used for the medication overviews.
- NIH Dietary Supplement Label Database (DSLD) — Official supplement product labels.
Content is written and reviewed by licensed HelloPharmacist pharmacists. See our data sources and editorial standards for how this information is built and checked.
Parts of this content are provided by the Therapeutic Research Center, LLC.
DISCLAIMER: Currently this does not check for drug-drug interactions. This is not an all-inclusive comprehensive list of potential interactions and is for informational purposes only. Not all interactions are known or well-reported in the scientific literature, and new interactions are continually being reported. Input is needed from a qualified healthcare provider including a pharmacist before starting any therapy. Application of clinical judgment is necessary.
© 2021 Therapeutic Research Center, LLC
Sulfamethoxazole, Trimethoprim Is Linked to Lower Levels of 7 Nutrients
Natural Medicines records Sulfamethoxazole, Trimethoprim as a medicine that can lower these. This is not an interaction with Thiamine — it is a separate effect of the medicine, and it is a reason some people are advised to supplement rather than to avoid one:
Read the full Sulfamethoxazole, Trimethoprim nutrient depletion report ›
Thiamine is itself a nutrient we track — see which medications may deplete THIAMINE.
Depletion records come from the licensed Natural Medicines database. Do not start a supplement on the strength of this page — ask your pharmacist or doctor whether it applies to you.
Taking Thiamine and Sulfamethoxazole, Trimethoprim Together: Common Questions
Can you take Thiamine with Sulfamethoxazole, Trimethoprim?
How serious is the Thiamine and Sulfamethoxazole, Trimethoprim interaction?
Written and reviewed by the HelloPharmacist editorial staff. Our editorial policy
Still Have a Question About Sulfamethoxazole, Trimethoprim and Thiamine?
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This information is for education only and is not a substitute for professional medical advice. Always check with your pharmacist or doctor before starting, stopping, or combining supplements and medications.