Major interaction on record — check this product against your medications before combining. Check your meds →
Dietary supplement

L-Threonine 500 mg Ingredients & Drug Interactions

by Douglas Laboratories

L-Threonine 500 mg label
See full label image
Capsule Category: Amino Acid/protein
Most serious interaction: Major
Clinical methodology reviewed by · Updated Sep 9, 2026 · Label data from the NIH DSLD
What is this page for?

First and foremost: checking L-Threonine 500 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: Major

L-Threonine 500 mg is a dietary supplement by Douglas Laboratories with 1 active ingredient. Its ingredients are commonly taken for general amino acid/protein support, muscle and tissue health, immune support.Based on those ingredients, 3 medications have a known interaction with it, the most serious rated major. The ingredients most likely to interact are L-Threonine. Use the checker below to test your specific medication, or read the full HelloPharmacist Interaction Report.

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Check Your Meds Against L-Threonine 500 mg by Douglas Laboratories

Ask about any prescription or over-the-counter medication and we check it for interactions with L-Threonine 500 mg by Douglas Laboratories — and tell you which ingredient is responsible.

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HelloPharmacist Scorecard of L-Threonine 500 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 Aug 13, 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: L-threonine, an amino acid at 500 mg per capsule. The capsule also holds inactive ingredients — gelatin, microcrystalline cellulose (a binder), and vegetable stearate.

Does it work?

Couldn't assess
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
Not assessable

This is a single-ingredient Threonine product and its label doesn't state a use — see Threonine's own graded uses on its monograph.

Why this rating?
  • We looked at the product name, claims, and label statements and couldn't find a stated purpose to grade.

The evidence for L-threonine supplementation is limited. For amyotrophic lateral sclerosis (ALS, also called Lou Gehrig's disease), it's rated possibly ineffective.

For multiple sclerosis, familial spastic paraparesis, and spasticity, there isn't enough reliable evidence in our data to say whether it works or not.

The evidence, ingredient by ingredient Threonine

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.

Threonine from food is well tolerated; the safety of higher-dose supplements is not well studied. The most common side effect reported is headache.

Some people have experienced mild gastrointestinal upset — diarrhea, gas, or constipation — when taking threonine supplements. Because supplement safety at higher doses hasn't been well researched, the facts recommend avoiding threonine supplements in pregnancy unless your doctor advises it.

The same caution applies to breastfeeding — there isn't enough data on supplement use during nursing, so talk it over with your doctor or pharmacist for personalized guidance.

Side effects, ingredient by ingredient Threonine

Meds to double-check

Major interaction found
Known Interaction Concern · database check
Major identified

At least one ingredient has a documented Major-severity interaction. Check your medications for a personalized result.

Why this rating?
  • 1 of the 1 matched ingredient can interact with medications — Threonine.
  • The most serious interaction on file is rated Major.
  • 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.

Before taking this product, check with your doctor or pharmacist if you take any NMDA antagonist medications. This is a Major-severity interaction — threonine may reduce how well these drugs work.

Check your own medication Run your meds through the checker above

The bottom line

Scorecard at a glanceFully disclosed formula with no assessable stated purpose. Major medication interactions have been identified, and safety information is well characterized.

L-threonine supplements may interest people researching support for certain neurological conditions, though the evidence is limited. If you take an NMDA antagonist, check with your doctor or pharmacist first — there's a Major interaction concern.

Because higher-dose supplement safety isn't well established, talk with your healthcare provider about whether this is right for you and whether the dose fits your situation.

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 L-Threonine 500 mg, straight from the product label.

Brand Douglas Laboratories
Barcode (UPC) 310539005774
Net contents 60 Capsule(s)
Market status On market
Date entered into DSLD Aug 23, 2020
DSLD ID 232306
Product type Amino Acid/protein
Supplement form Capsule
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 L-Threonine 500 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 Capsule(s)
Maximum serving Sizes:
1 Capsule(s)
Servings per container
60
UPC/BARCODE
310539005774
IngredientAmount% DV
L-Threonine500 mg--

Other ingredients: Gelatin, Microcrystalline Cellulose, Vegetable Stearate

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 capsule 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

L-Threonine 500 mg by Douglas Laboratories label

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

L-Threonine 500 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 L-Threonine 500 mg by Douglas Laboratories

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

Serving size1 Capsule(s) Dosage formCapsule Servings per container60 Amounts shown are per serving.

L-Threonine

Interacts with
3 drugs
500 mg per serving

Threonine is an essential amino acid your body needs but cannot make, so you must get it from food or supplements. Most people get plenty from a norma...

L-Threonine monograph & interactions

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

Interaction report

L-Threonine 500 mg by Douglas Laboratories Drug Interactions

Want to check YOUR meds against L-Threonine 500 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 Major

Ingredients driving the most interactions

L-Threonine 3

Individual Drug Interactions

The ingredients in L-Threonine 500 mg interact with 3 drugs. Click any drug to see the details.

1 of the 1 ingredient in L-Threonine 500 mg interact with drugs. Each result below shows which ingredient is responsible. L-Threonine

Each ingredient & the kinds of drugs it affects

For each ingredient in L-Threonine 500 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.

L-Threonine1 drug type · 3 drugs

Nmda Antagonists

Theoretically, threonine might decrease the effects of NMDA antagonists.
Threonine increases central nervous system (CNS) glycine levels. Glycine seems to bind a site on NMDA receptors and enhance the activity of the receptors.

Likelihood Likely Evidence B
L-Threonine full monograph & interactions
The maker

Brand information

Manufacturer and brand details for L-Threonine 500 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

L-Threonine 500 mg by Douglas Laboratories: Common Questions

Does L-Threonine 500 mg by Douglas Laboratories interact with any medications?
Yes. Based on its ingredients, L-Threonine 500 mg has a known interaction with 3 medications, including 3 rated major. Use the checker to see how it interacts with a specific drug.
How can one product interact with so many drugs?
L-Threonine 500 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.
What is L-threonine and what is it supposed to do?
L-threonine is an amino acid — one of the building blocks of protein. It's used to support certain nerve and muscle conditions, though the evidence for its effectiveness is mixed. Our data shows it's rated possibly ineffective for ALS and insufficient evidence for multiple sclerosis, spasticity, and familial spastic paraparesis.
Are there side effects?
Yes. Headache is the most commonly reported side effect. Some people also experience mild gastrointestinal upset — diarrhea, gas, or constipation. The safety profile of these higher-dose supplements hasn't been thoroughly studied, so expect the unexpected and watch how you feel.
Can I take this while pregnant or breastfeeding?
There isn't enough data on supplement-level threonine use in pregnancy or breastfeeding to know whether it's safe. The recommendations advise against it unless your doctor specifically advises otherwise. Talk with your doctor or pharmacist for personalized advice based on your situation.
Why is threonine a concern with certain medications?
Threonine raises glycine levels in your brain, and glycine enhances NMDA receptors (a type of nerve receptor). If you take an NMDA antagonist — a medication designed to block those receptors — threonine might counteract it and reduce effectiveness. If you take one of these medications, check with your doctor first.
Is this the same as the threonine in my food?
Yes, it's the same amino acid, but the amount is different. Threonine from food is safe and well tolerated. Supplement doses haven't been studied nearly as much, so safety at higher levels isn't as well established. That's why the caution applies to the supplement form, not the food form.

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.

L-Threonine 500 mg label
Go deeper

The Full Monographs Behind L-Threonine 500 mg’s Ingredients

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

Herb & supplement monograph

Threonine

Interacts with 3 drugs

Threonine is an essential amino acid your body needs but cannot make, so you must get it from food or supplements. Most people get plenty from a normal diet, and high-quality evidence for ta...

Read the full Threonine monograph →
Sources

Sources & How We Checked

L-Threonine 500 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 4 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.

Threonine 4 references
  1. Tandan R, Bromberg MB, Forshew D, et al. A controlled trial of amino acid therapy in amyotrophic lateral sclerosis: I. Clinical, functional, and maximum isometric torque data. Neurology 1996;47:1220-6. PubMed
  2. Lee A, Patterson V. A double blind study of L-threonine in patients with spinal spasticity. Acta Neurol Scand 1993;88:334-8. PubMed
  3. Blin O, Pouget J, Aubrespy G, et al. A double-blind placebo controlled trial of L-threonine in amyotrophic lateral sclerosis. J Neurol 1992;239:79-81.
  4. Roufs JB. L-threonine as a symptomatic treatment for amyotrophic lateral sclerosis (ALS). Med Hypotheses 1991;34:20-3. PubMed

See these in context on the Threonine 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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