Drug & supplement interaction

Soy + Sulfadiazine, Trimethoprim

Sulfadiazine, Trimethoprim brand name: Coptin.

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

Soy has a minor interaction with Sulfadiazine, Trimethoprim. Theoretically, antibiotics may decrease the activity of soy isoflavones.

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

Soy and Sulfadiazine, Trimethoprim

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

Minor

ANTIBIOTIC DRUGS

Why this applies to Sulfadiazine, Trimethoprim

Sulfadiazine, Trimethoprim falls under ANTIBIOTIC DRUGS — the group Soy interacts with.

Theoretically, antibiotics may decrease the activity of soy isoflavones.
Intestinal bacteria are responsible in part for converting soy isoflavones into their active forms. Antibiotics may decrease the amount of intestinal bacteria and decrease its ability to convert isoflavones.
Severity Minor Likelihood Possible Evidence D

Interaction 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.

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

Here's the gist of this one, and it's pretty mild. The interaction goes in the opposite direction from what most people worry about. Soy isn't hurting your antibiotic. Instead, your antibiotic might dampen what soy does for you. When you take a sulfadiazine and trimethoprim combo (like Coptin), it can knock down some of the friendly bacteria in your gut. Those same bacteria help convert soy isoflavones into their more active forms, so soy may simply work a bit less well while you're on the antibiotic.

Honestly, this is theoretical and based on lab data, so I wouldn't lose sleep over it. Your infection treatment stays just as effective, and eating soy foods is still fine. If you take concentrated soy isoflavone supplements for a specific reason, just mention it to your pharmacist or doctor.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Morito K, Hirose T, Kinjo J, et al. Interaction of phytoestrogens with estrogen receptors alpha and beta. Biol Pharm Bull 2001;24:351-6. PubMed

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

Soy Also Interacts With Other Medications

Soy has 9 major, 343 moderate, 258 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.

Major 9 Moderate 343 Minor 258 No known interaction 2,220 (incl. Sulfadiazine, Trimethoprim)
Taking anything else?

Check Another of Your Medications Against Soy

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

Everything else you take

See Every Supplement That Interacts With Sulfadiazine, Trimethoprim

This page covers Soy 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 Soy as Part of a Dietary Supplement Product? Check It for Interactions

We hold 821 real supplement products containing Soy, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Soy. Your product may carry other ingredients that interact with Sulfadiazine, Trimethoprim too, on top of Soy — 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 Soy 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 Soy
Top 25%

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

29 days ago today
Medication Sulfadiazine, Trimethoprim
Top 10%

#254 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 Soy

What is Soy?

  • Menopause symptoms (hot flashes)
  • Heart and cholesterol health
  • Bone health
  • Plant-based protein source
  • General nutrition

Soy is a nutritious bean that is a staple food and a popular source of plant protein and isoflavones. Eating soy foods as part of a balanced diet is generally considered safe for most people, and there is moderate evidence it may modestly help cholesterol and some menopause symptoms, though results vary. Talk with your pharmacist or doctor before using concentrated soy isoflavone supplements, especially if you have a history of hormone-sensitive conditions.

Read the full Soy monograph & all interactions
Keep checking

Other Drugs & Soy

Browse every other medication we’ve checked against Soy — both the ones with a known interaction and the ones without. Select any drug for the full detail.

9Major
343Moderate
258Minor
2,219No known interaction
9 Major 343 Moderate 258 Minor 2,219 No interaction
Major

9 interactions

Moderate

343 interactions

Showing 60 of 343 moderate interactions — see all 343 on the Soy page.

Minor

258 interactions

Showing 60 of 258 minor interactions — see all 258 on the Soy page.

No interaction 2,219 drugs checked — show the list

We also checked Soy against these medications and found no known interaction in our sources. Open any page to confirm.

Showing the 60 most looked-up of 2,219 medications checked with no known interaction — see the full Soy list.

See the full Soy 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
Soy 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 Soy and Sulfadiazine, Trimethoprim Together: Common Questions

Can you take Soy 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 Soy 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 Soy?

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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.