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Dietary supplement

Vitamin B1 100 mg Ingredients & Drug Interactions

by Douglas Laboratories

Vitamin B1 100 mg label
See full label image
Tablet Or Pill Category: Vitamin
Most serious interaction: Minor
Clinical methodology reviewed by · Updated Sep 16, 2026 · Label data from the NIH DSLD
What is this page for?

First and foremost: checking Vitamin B1 100 mg against your medications. The heart of this page is the interaction checker and the full interaction report — how this product’s ingredients may interact with prescription and over-the-counter medicines you may be taking.

Around that, we add a pharmacist’s high-level view of the product as a whole — what’s inside, the evidence for its stated use, how transparent the label is, and what safety data exists — so you can see the full picture in one place. It’s educational information from our licensed clinical databases and the clinical staff at HelloPharmacist — not medical advice — and we don’t sell or endorse products. Our editorial policy

The interaction bottom line Most serious interaction: Minor

Vitamin B1 100 mg is a dietary supplement by Douglas Laboratories with 1 active ingredient. Its ingredients are commonly taken for preventing or treating thiamine deficiency, beriberi, wernicke-korsakoff syndrome (alcohol-related).Based on those ingredients, 3 medications have a known interaction with it, the most serious rated minor. The ingredients most likely to interact are Thiamine. Use the checker below to test your specific medication, or read the full HelloPharmacist Interaction Report.

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Check Your Meds Against Vitamin B1 100 mg by Douglas Laboratories

Ask about any prescription or over-the-counter medication and we check it for interactions with Vitamin B1 100 mg by Douglas Laboratories — and tell you which ingredient is responsible.

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HelloPharmacist Scorecard of Vitamin B1 100 mg by Douglas Laboratories

Our pharmacy team’s full take, with four database checks built into the cards below — a summary of what is known, not a grade of the product itself.

From our pharmacy team — supplement deep dive

Generated from HelloPharmacist’s pharmacist-curated databases and editorial rules · Last generated Jul 11, 2026

What’s inside

Full disclosure
Ingredient Transparency · database check
Full

Every active ingredient lists its own amount on the label.

Why this rating?
  • The label discloses an exact amount for 1 of its 1 active ingredient.
  • No proprietary blends here — you can verify the dose of every single component.

This product contains one active ingredient: thiamine (also called vitamin B1), which is an essential nutrient your body needs to convert food into energy and keep your nerves working properly. The tablet also contains several inactive ingredients—microcrystalline cellulose, croscarmellose sodium, stearic acid, vegetable stearate, and silica—which help hold the tablet together and make it easier to swallow.

Does it work?

Strong evidence
Evidence for Intended Use · database check
By FDA rules, dietary supplements can’t claim to treat, cure, or prevent disease — so labels speak in careful marketing language. We discern each product’s intended use from its name, label claims, and label statements, then grade the clinical evidence for that use. How these ratings are computed
Strong

Clinical evidence supports at least one of this product's ingredients for its stated purpose.

Why this rating?
  • The label markets this product for: Thiamine supplementation and nerve function support.
  • We looked for evidence on: Thiamine deficiency, Wernicke-Korsakoff syndrome (WKS), Fatigue, Energy metabolism, Neurological health.
  • The strongest evidence on file: Thiamine is rated "Effective" for Thiamine deficiency (Natural Medicines).
  • Also on file: Thiamine is rated "Effective" for Wernicke-Korsakoff syndrome (WKS).
  • Also on file: Thiamine is rated "Insufficient Reliable Evidence To Rate" for Fatigue.

Thiamine is effective for treating thiamine deficiency and Wernicke-Korsakoff syndrome (WKS), a serious brain condition caused by severe thiamine lack. The evidence is possibly effective for dysmenorrhea (painful periods), but possibly ineffective for heart failure and as a mosquito repellent.

If you're looking to use it for something other than deficiency or WKS, talk with your pharmacist or doctor about whether the science backs it.

The evidence, ingredient by ingredient Thiamine

How safe is it?

Well-documented data
Safety Information · database check
Well characterized

Adverse-effect, pregnancy, and general safety data are on file for most of these ingredients.

Why this rating?
  • We hold adverse-effect (side-effect) data for 1 of the 1 matched ingredient.
  • Pregnancy & breastfeeding safety ratings cover 1 of 1.
  • General safety write-ups exist for 1 of 1.
  • Remember: this measures how much safety information exists. Thin data is not the same as being safe.

Thiamine is generally very well tolerated when you take it by mouth at normal doses. Allergic reactions like dermatitis are rare when taken orally, though they're possible.

Your body needs thiamine during pregnancy and while breastfeeding, so if you're pregnant or nursing and want to supplement, use only the amounts your doctor or pharmacist recommends.

Side effects, ingredient by ingredient Thiamine

Meds to double-check

Minor interactions only
Known Interaction Concern · database check
Minor only

Only Minor-severity interactions are documented for these ingredients.

Why this rating?
  • 1 of the 1 matched ingredient can interact with medications — Thiamine.
  • The most serious interaction on file is rated Minor.
  • For scale: 3 individual medications appear in the full list. A big number alone doesn't make a product dangerous — what matters is whether YOUR medication is on it, so run yours through the interaction checker on this page.

If you take trimethoprim (Proloprim), check with your pharmacist before starting this product—it may raise your thiamine levels. No other major interactions are documented for the ingredients we checked.

Check your own medication Run your meds through the checker above

The bottom line

Scorecard at a glanceFully disclosed formula with clinical evidence supporting its stated purpose. Only minor medication interactions are documented, and safety information is well characterized.

This is a straightforward B1 supplement, most useful if you have a confirmed thiamine deficiency or Wernicke-Korsakoff syndrome. If you take trimethoprim (an antibiotic), let your pharmacist know before starting this supplement.

Otherwise, it's generally a well-tolerated option for supporting your B1 needs.

Educational only — not medical advice; always confirm with your pharmacist. Our editorial policy · How we use AI

Assessment coverage: 1 of 1 active ingredient matched to our full ingredient reviews (monographs). Based on the product label dated Aug 23, 2020.

This Scorecard evaluates available label information, ingredient evidence, and known medication-safety considerations. It does not independently verify product identity, purity, potency, contamination, or manufacturing quality. How these ratings are computed

At a glance

General information

Key facts about Vitamin B1 100 mg, straight from the product label.

Brand Douglas Laboratories
Barcode (UPC) 310539015483
Net contents 100 Tablet(s)
Market status On market
Date entered into DSLD Aug 23, 2020
DSLD ID 232586
Product type Vitamin
Supplement form Tablet Or Pill
Dietary claims / uses All Other, Structure/Function
Intended target group(s) Adult (18 - 50 Years), Gluten Free
From the label
Everything in this section is reproduced from the manufacturer’s own product label — it’s the label speaking, not HelloPharmacist. We show it so you can see exactly what the maker states; we don’t verify or endorse those statements.

Supplement Facts

The label details for Vitamin B1 100 mg by Douglas Laboratories, sourced from the NIH Dietary Supplement Label Database.

Supplement Facts

Daily Value (DV) Target Group(s):
Adults and children 4 or more years of age
Minimum serving Sizes:
1 Tablet(s)
Maximum serving Sizes:
1 Tablet(s)
Servings per container
100
UPC/BARCODE
310539015483
IngredientAmount% DV
Thiamine100 mg8333%

Other ingredients: Microcrystalline Cellulose, Croscarmellose Sodium, Stearic Acid, Vegetable Stearate, Silica

Tap any ingredient to jump to its full detail below.

Label statements
These statements are the manufacturer’s wording, reproduced from the product label — the label is saying it, not HelloPharmacist. We don’t verify or endorse them.
Suggested/Recommended/Usage/Directions

Suggested Usage: As a dietary supplement, adults take 1 tablet daily or as directed by your health professional.

Precautions

Warning: If you are pregnant, nursing, have any health condition or taking any medication, consult your health professional before using this product.

Keep out of the reach of children.

Use only if safety seal is intact.

Storage

Store in a cool, dry place.

Formulation

Gluten-free, Non-GMO

FDA Disclaimer Statement

This statement has not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.

General Statements

Scan to learn about our manufacturing excellence Contents may not fill package in order to accommodate required labeling. Please rely on stated quantity.

FDA Statement of Identity

Dietary Supplement

Is this label outdated? Report a formula or label change and our pharmacy team will review it.

See for yourself

Vitamin B1 100 mg by Douglas Laboratories label

The label scan from the NIH Dietary Supplement Label Database. Tap to enlarge.

Vitamin B1 100 mg label

Label images are published by the NIH Dietary Supplement Label Database for the version of this product on file. Always read your actual product label.

View the full label (PDF)
What’s inside

The Ingredients in Vitamin B1 100 mg by Douglas Laboratories

This is the 1 active ingredient this product is made of. Select it to open its full monograph.

Serving size1 Tablet(s) Dosage formTablet Or Pill Servings per container100 Amounts shown are per serving.

Thiamine

Interacts with
3 drugs
100 mg per serving Form: Thiamine Hydrochloride, Vitamin B1

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 eno...

Thiamine monograph & interactions

Other (inactive) ingredients: Microcrystalline Cellulose, Croscarmellose Sodium, Stearic Acid, Vegetable Stearate, Silica. These complete the product’s ingredient list but are not active constituents.

Interaction report

Vitamin B1 100 mg by Douglas Laboratories Drug Interactions

Want to check YOUR meds against Vitamin B1 100 mg?

Ask about interactions with your drugs in plain English — “Can I take it with lisinopril?” — and we find you the answer in seconds, ingredient by ingredient.

 Go to the checker
3Drugs
3 Minor

Ingredients driving the most interactions

Thiamine 3

Individual Drug Interactions

The ingredients in Vitamin B1 100 mg interact with 3 drugs. Click any drug to see the details.

1 of the 1 ingredient in Vitamin B1 100 mg interact with drugs. Each result below shows which ingredient is responsible. Thiamine

Each ingredient & the kinds of drugs it affects

For each ingredient in Vitamin B1 100 mg with known interactions, here are the types of medications it can affect. Open any type for the detail — or search your exact drug in the checker above.

Thiamine1 drug type · 3 drugs

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.

Likelihood Probable Evidence B
Thiamine full monograph & interactions
The maker

Brand information

Manufacturer and brand details for Vitamin B1 100 mg, from the product label.

Douglas Laboratories

See all Douglas Laboratories products
Name
Douglas Laboratories
Street Address
600 Boyce Road
City
Pittsburgh
State
PA
ZipCode
15205
Phone Number
1.800.245.4440
Web Address
www.douglaslabs.com
Pharmacist Counseling Corner

Vitamin B1 100 mg by Douglas Laboratories: Common Questions

Does Vitamin B1 100 mg by Douglas Laboratories interact with any medications?
Yes. Based on its ingredients, Vitamin B1 100 mg has a known interaction with 3 medications. Use the checker to see how it interacts with a specific drug.
How can one product interact with so many drugs?
Vitamin B1 100 mg contains a single active ingredient, and that one ingredient can interact with many different medications on its own. We check it against each medication and show the mechanism responsible.
Where does this information come from?
The product label data comes from the NIH Dietary Supplement Label Database (DSLD); the interaction data is built on the Natural Medicines database and reviewed by HelloPharmacist pharmacists.
Is this safe to take while I'm pregnant or breastfeeding?
Thiamine is likely safe during pregnancy and breastfeeding because your body actually needs it. Just use supplement doses only as your doctor or pharmacist advises rather than megadoses on your own.
Will this help with my period cramps?
The evidence is possibly effective for dysmenorrhea (period pain), so it might help, but the research isn't as strong as it is for deficiency. Talk with your doctor about whether it's worth trying for your situation.
Can I take this as a mosquito repellent?
No—the evidence says thiamine is possibly ineffective as a mosquito repellent, so don't count on it for that.
What is thiamine used for in the body?
Thiamine is a B vitamin that helps your body convert food into energy and keeps your nerves functioning properly. It's essential for health, and your body can't store much of it, so you need to get it regularly from food or supplements.
Are there any fillers in this tablet?
Yes, there are inactive ingredients: microcrystalline cellulose, croscarmellose sodium, stearic acid, vegetable stearate, and silica. These help form and stabilize the tablet.
What are the side effects of thiamine?
When taken by mouth at normal doses, thiamine is very safe, though allergic reactions like dermatitis are rare. Injectable forms can rarely cause more serious allergic reactions, but you're taking this as a tablet.

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

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Label information is sourced from the NIH Dietary Supplement Label Database and reflects the product version on file; always read your actual product label. This page is for education only and is not a substitute for professional medical advice. Confirm with your pharmacist or doctor before combining supplements and medications.

Vitamin B1 100 mg label
Go deeper

The Full Monographs Behind Vitamin B1 100 mg’s Ingredients

Every ingredient we hold a full HelloPharmacist monograph for — uses, evidence, safety, and the complete interaction list.

Herb & supplement monograph

Thiamine

Interacts with 3 drugs

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 clear...

Read the full Thiamine monograph →
Sources

Sources & How We Checked

Vitamin B1 100 mg's label data comes from the NIH Dietary Supplement Label Database; the ingredient interaction data is from the Natural Medicines database, reviewed by our pharmacists.

Content is written and reviewed by licensed HelloPharmacist pharmacists. See our data sources and editorial standards for how this information is built and checked.

The 7 references behind this product’s interaction data

Every citation that drives the interaction findings for this product’s ingredients, from the evidence-graded Natural Medicines (TRC Healthcare) database. Open an ingredient to browse its citations — links open the study on PubMed or the publisher’s site.

Thiamine 7 references
  1. McEvoy GK, ed. AHFS Drug Information. Bethesda, MD: American Society of Health-System Pharmacists, 1998.
  2. Yates AA, Schlicker SA, Suitor CW. Dietary reference intakes: The new basis for recommendations for calcium and related nutrients, B vitamins, and choline. J Am Diet Assoc 1998;98:699-706. PubMed
  3. Food and Nutrition Board, Institute of Medicine. Dietary Reference Intakes for Thiamin, Riboflavin, Niacin, Vitamin B6, Folate, Vitamin B12, Pantothenic Acid, Biotin, and Choline (2000). Washington, DC: National Academy Press, 2000. Available at: http://b
  4. Rogovik, A. L., Vohra, S., and Goldman, R. D. Safety considerations and potential interactions of vitamins: should vitamins be considered drugs? Ann.Pharmacother. 2010;44(2):311-324. PubMed
  5. Arruti N, Bernedo N, Audicana MT, Villarreal O, Uriel O, Muñoz D. Systemic allergic dermatitis caused by thiamine after iontophoresis. Contact Dermatitis. 2013 Dec;69(6):375-6. PubMed
  6. Thiamine hydrochloride injection package insert. Lake Zurich, IL: Fresenius Kabi, LLC; September 2019.
  7. 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.

See these in context on the Thiamine monograph →

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

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