Drug & supplement interaction

Thiamine + Sulfadiazine, Trimethoprim

Sulfadiazine, Trimethoprim brand name: Coptin.

Minor Interaction
Medically reviewed by · Updated October 2026
The bottom line Minor

Thiamine has a minor interaction with Sulfadiazine, Trimethoprim. Trimethoprim might increase blood levels of thiamine.

Read the full interaction report
SeverityMinor
LikelihoodProbable
EvidenceB
What do Severity, Likelihood & Evidence mean?
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Interaction report

Thiamine and Sulfadiazine, Trimethoprim

Here is the interaction we found between these two, with the evidence behind it.

Minor

TRIMETHOPRIM (Proloprim)

Trimethoprim might increase blood levels of thiamine.
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.
Severity Minor Likelihood Probable Evidence B

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..

Dr. Brian Staiger, PharmD, BCPS
Dr. Brian Staiger explains PharmD, Clinical Pharmacist

Here's a small wrinkle worth knowing about. The trimethoprim part of this combination (the same drug found in Coptin) can interfere with the transporters that move thiamine (vitamin B1) into your gut, liver, and kidneys. The net result is a bit unexpected: thiamine levels in your blood may actually nudge upward rather than drop. This isn't a case of the drug stealing your vitamin.

The good news is this is rated a minor interaction, and thiamine is water-soluble, so your body simply passes any extra in your urine. For most people taking a normal B1 supplement, this won't cause noticeable problems or change how well your antibiotic fights infection. If you're on thiamine for a real deficiency, just mention it to your pharmacist so they can keep an eye on things.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. 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.

Severity how clinically significant the interaction is
Major

Clinically significant. Avoid the combination, or use only under close professional supervision.

Moderate

Usually worth avoiding or managing — may need monitoring, a dose change, or timing apart.

Minor

Generally not serious. Be aware of it and mention it to your pharmacist.

Likelihood how strong the evidence is that the interaction actually happens in people
  • 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.
Evidence the quality of the studies behind the rating (graded A–D)
  • 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.

Keep it in perspective

Thiamine Also Interacts With Other Medications

Thiamine has 2 minor known drug interactions in our database — the Sulfadiazine, Trimethoprim one above is one of them. If you take anything else, check it against the full list below.

Minor 2 No known interaction 2,828 (incl. Sulfadiazine, Trimethoprim)
Taking anything else?

Check Another of Your Medications Against Thiamine

Covers the 2,830 medications we’ve checked against Thiamine. Pick one to open its full report.

Everything else you take

See Every Supplement That Interacts With Sulfadiazine, Trimethoprim

This page covers Thiamine only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Sulfadiazine, Trimethoprim page lists 63 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), Cesium (major) and Ephedra (major).

By severity: 8 major · 44 moderate · 11 minor.

From our pharmacist’s overview on the Sulfadiazine, Trimethoprim page

“Sulfadiazine with trimethoprim (Coptin) earns more wariness than most antibiotics do, and the eight major-rated interactions on this list of 63 are the ones to understand first. Most of them share a single mechanism.”

Reviewed by 2 · Jul 18, 2026

Open the Sulfadiazine, Trimethoprim interaction page

One more smart check

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 Sulfadiazine, 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:

How much people look this up

Where Thiamine and Sulfadiazine, 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.

Supplement Thiamine
Top 25%

#164 of 1,452 supplements looked up here in the last 7 days

29 days ago today
Medication Sulfadiazine, Trimethoprim
Top 5%

#105 of 2,830 medications looked up here in the last 7 days

29 days ago today

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.

Supplement

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.

Read the full Thiamine monograph & all interactions
Keep checking

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.

0Major
0Moderate
2Minor
2,827No known interaction
2 Minor 2,827 No interaction
Minor

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.

Showing the 60 most looked-up of 2,827 medications checked with no known interaction — see the full Thiamine list.

See the full Thiamine interactions page
See every supplement checked against Sulfadiazine, Trimethoprim, ranked by severity
Sources

Sources & How We Checked

Interaction details are evidence-graded and sourced from the Natural Medicines database. The medication overview comes from MedlinePlus.

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

Keep exploring
Thiamine monograph › Uses, safety, and every drug interaction in one place Sulfadiazine, Trimethoprim supplement interactions › Every supplement checked against Sulfadiazine, Trimethoprim, ranked by severity Supplement interaction checker › Check any supplement or product against your medications Browse medications A–Z › Every drug we've checked against herbs & supplements Ask a pharmacist › Free, personal answer from our licensed team
Pharmacist Counseling Corner

Taking Thiamine and Sulfadiazine, Trimethoprim Together: Common Questions

Can you take Thiamine with Sulfadiazine, Trimethoprim?
There is only a minor interaction, which is usually not serious. Read the full details on this page and confirm with your pharmacist before combining them.
How serious is the Thiamine and Sulfadiazine, Trimethoprim interaction?
We rate it Minor. This interaction is generally not clinically significant, but it remains worth noting and discussing with your pharmacist.

Written and reviewed by the HelloPharmacist editorial staff. Our editorial policy

Still Have a Question About Sulfadiazine, 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.