Interactions on record — worth a quick check against your medications. Check your meds →
Dietary supplement

Vitamin B-1 300 mg Ingredients & Drug Interactions

by GNC

Vitamin B-1 300 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 B-1 300 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 B-1 300 mg is a dietary supplement by GNC 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.

Jump to a section

Check Your Meds Against Vitamin B-1 300 mg by GNC

Ask about any prescription or over-the-counter medication and we check it for interactions with Vitamin B-1 300 mg by GNC — and tell you which ingredient is responsible.

Pharmacist-reviewed data Checks every ingredient Answer in seconds
Prefer a human? Send your question to our licensed pharmacists — free, answered by email within 24 hours.

HelloPharmacist Scorecard of Vitamin B-1 300 mg by GNC

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 (vitamin B-1), a B vitamin your body uses to convert food into energy and support nerve and heart function. Thiamine is an essential nutrient — your body can't make it, so you have to get it from food or supplements.

The tablet also contains inactive ingredients like microcrystalline cellulose (a filler), magnesium stearate (a flow agent), and rice bran powder.

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: Essential for proper nerve and muscle function.
  • We looked for evidence on: Thiamine deficiency, Wernicke-Korsakoff syndrome (WKS), Diabetic neuropathy, Beriberi, Peripheral neuropathy, Nerve damage.
  • 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 Diabetic neuropathy.

Thiamine at this dose is effective for treating thiamine deficiency and for managing Wernicke-Korsakoff syndrome, a serious neurological condition caused by severe thiamine shortage. The evidence also suggests it may help with dysmenorrhea (painful periods), though the evidence here is not as strong.

For mosquito repellent and heart failure, the evidence does not support its use.

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 taken by mouth in normal amounts. Allergic reactions and skin rashes are rare when taken orally, though injectable thiamine (given by a healthcare provider) can occasionally cause more serious reactions.

Thiamine is needed during pregnancy and breastfeeding — if you're pregnant or nursing and considering a supplement, talk with your provider about the right dose for you.

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 (an antibiotic), verify the interaction with your pharmacist before starting this supplement — it can raise your thiamine blood levels. No other major interactions are documented for the ingredients we could check.

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, single-ingredient B vitamin supplement used mainly to prevent or treat thiamine deficiency and Wernicke-Korsakoff syndrome. If you take trimethoprim or any antibiotic, check with your pharmacist before you add this.

Otherwise, it's generally well tolerated.

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 Jun 24, 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 B-1 300 mg, straight from the product label.

Brand GNC
Barcode (UPC) 048107177256
Net contents 100 Vegetarian Tablet(s)
Market status On market
Date entered into DSLD Jun 24, 2020
DSLD ID 224651
Product type Vitamin
Supplement form Tablet Or Pill
Dietary claims / uses All Other, Structure/Function
Intended target group(s) Adult (18 - 50 Years), Kosher, Gluten Free, Dairy Free, Sugar 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 B-1 300 mg by GNC, 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)
UPC/BARCODE
048107177256
IngredientAmount% DV
Thiamine300 mg25000%

Other ingredients: Microcrystalline Cellulose, Hydroxypropyl Methylcellulose, Hydroxypropylcellulose, Stearic Acid, Magnesium Stearate, Rice Bran Powder

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.
Precautions

Keep out of reach of children.

Storage

Store in a cool, dry place.

Formulation

Essential for proper nerve & muscle function

Potency verified by GNC procedure #5103. Conforms to USP <2091> for weight. Meets USP <2040> disintegration.

No sugar, no starch, no artificial colors, no artificial flavors, no preservatives, sodium free, no wheat, gluten free, no corn, no soy, no dairy. GF Gluten free

General Statements

100-day supply

FDA Statement of Identity

Dietary Supplement

Suggested/Recommended/Usage/Directions

Directions: As a dietary supplement, take one tablet daily.

Seals/Symbols

Ko Kosher Service

Formula

Ko Kosher Service

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.

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

See for yourself

Vitamin B-1 300 mg by GNC label

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

Vitamin B-1 300 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 B-1 300 mg by GNC

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 Amounts shown are per serving.

Thiamine

Interacts with
3 drugs
300 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, Hydroxypropyl Methylcellulose, Hydroxypropylcellulose, Stearic Acid, Magnesium Stearate, Rice Bran Powder. These complete the product’s ingredient list but are not active constituents.

Interaction report

Vitamin B-1 300 mg by GNC Drug Interactions

Want to check YOUR meds against Vitamin B-1 300 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 B-1 300 mg interact with 3 drugs. Click any drug to see the details.

1 of the 1 ingredient in Vitamin B-1 300 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 B-1 300 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 B-1 300 mg, from the product label.

GNC

See all GNC products
Name
General Nutrition Corporation
City
Pittsburgh
State
PA
ZipCode
15222
Phone Number
1-888-462-2548
Web Address
gnc.com
Pharmacist Counseling Corner

Vitamin B-1 300 mg by GNC: Common Questions

Does Vitamin B-1 300 mg by GNC interact with any medications?
Yes. Based on its ingredients, Vitamin B-1 300 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 B-1 300 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.
Will this supplement help my energy levels?
Thiamine helps your body convert food into energy, but this supplement is most effective if you actually have a thiamine deficiency. If your energy is low for other reasons, this won't necessarily help. If you're concerned about a deficiency, talk with your doctor or pharmacist.
Is it safe to take while I'm pregnant?
Thiamine is needed during pregnancy, and the safety data rates this ingredient as likely safe. That said, talk with your provider about whether you need a supplement and what dose is right for you — don't self-dose without guidance.
Can I take this if I'm breastfeeding?
Thiamine is needed while breastfeeding. Use supplements at recommended amounts under your provider's guidance so you're getting enough for both you and your baby.
What's the difference between this and thiamine from food?
The vitamin is the same whether it comes from food like whole grains, pork, and nuts or from a supplement. A supplement like this one is useful if you're not getting enough from your diet or if you have a diagnosed deficiency.
Are there any side effects?
Oral thiamine is very safe and side effects are rare. Allergic reactions like skin rashes are uncommon. If you notice any unusual symptoms after starting, let your pharmacist know.

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

Not sure if Vitamin B-1 300 mg is safe with your meds?

Our pharmacists answer your medication & supplement questions — free.

Ask a pharmacist

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 B-1 300 mg label
Go deeper

The Full Monographs Behind Vitamin B-1 300 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 B-1 300 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

Keep exploring
Supplement interaction checker › Check any supplement or product against your medications Drug–drug interactions › Check two or more of your medications against each other Browse medications A–Z › Every drug we've checked against herbs & supplements NDC & pricing lookup › Find a drug’s NDCs, packaging and costs Ask a pharmacist › Free, personal answer from our licensed team