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Dietary supplement

Double Strength L-Lysine 1000 mg Ingredients & Drug Interactions

by NOW

Double Strength L-Lysine 1000 mg label
See full label image
Tablet Or Pill Category: Amino Acid/protein
Most serious interaction: Minor
Clinical methodology reviewed by · Updated Sep 9, 2026 · Label data from the NIH DSLD
What is this page for?

First and foremost: checking Double Strength L-Lysine 1000 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

Double Strength L-Lysine 1000 mg is a dietary supplement by NOW with 1 active ingredient. Its ingredients are commonly taken for cold sores (herpes labialis), genital herpes outbreaks, supporting protein and collagen formation.Based on those ingredients, 1 medication has a known interaction with it, the most serious rated minor. The ingredients most likely to interact are L-Lysine. Use the checker below to test your specific medication, or read the full HelloPharmacist Interaction Report.

Jump to a section

Check Your Meds Against Double Strength L-Lysine 1000 mg by NOW

Ask about any prescription or over-the-counter medication and we check it for interactions with Double Strength L-Lysine 1000 mg by NOW — and tell you which ingredient is responsible.

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HelloPharmacist Scorecard of Double Strength L-Lysine 1000 mg by NOW

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 23, 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.
  • “L-Lysine” is listed as a grouped ingredient — the label gives one combined amount (1 Gram(s)) without saying how much of each component you get.

This product contains one active ingredient: L-lysine hydrochloride at 1,000 mg per tablet. Lysine is an amino acid your body uses for protein synthesis and immune function.

The tablet also includes several inactive ingredients — microcrystalline cellulose, silicon dioxide, stearic acid, a vegetarian coating, croscarmellose sodium, and magnesium stearate — that help form and preserve the tablet.

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

We hold no graded evidence for this product's ingredients for its stated purpose.

Why this rating?
  • The label markets this product for: amino acid for protein and collagen production.
  • Our graded evidence for these ingredients doesn't cover that particular purpose.

L-lysine is possibly effective for cold sores (herpes labialis), meaning there's some evidence it may help, though the proof isn't airtight. For other uses listed — child growth, pressure ulcers, and diabetic foot ulcers — the evidence we hold is insufficient to rate whether it works.

The evidence, ingredient by ingredient Lysine

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.

L-lysine is generally well tolerated at typical doses, though high amounts may cause stomach upset and diarrhea. The most common side effects reported with oral use are abdominal pain, diarrhea, and indigestion.

Long-term safety hasn't been well studied. If you're pregnant or breastfeeding, there isn't enough reliable data on supplement safety, so talk with your doctor or pharmacist before using it — lysine from food is fine, but supplement use in pregnancy and lactation isn't well established.

Side effects, ingredient by ingredient Lysine

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 — Lysine.
  • The most serious interaction on file is rated Minor.
  • For scale: 1 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 a 5-HT4 agonist (a serotonin gut-motility drug), check with your pharmacist or doctor before adding this supplement — lysine may reduce its effect. No other medication interactions are documented for the ingredients we could check, but always confirm your exact prescriptions.

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. Only minor medication interactions are documented, and safety information is well characterized.

L-lysine may help with cold sores if you want to try it. It's generally well tolerated, though it can cause stomach upset or diarrhea at higher doses.

If you take a 5-HT4 agonist or are pregnant or breastfeeding, check with your doctor or pharmacist before starting. It's a straightforward supplement, but it's worth confirming your specific situation first.

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 Feb 23, 2022.

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 Double Strength L-Lysine 1000 mg, straight from the product label.

Brand NOW
Barcode (UPC) 733739001139
Net contents 100 Tablet(s)
Market status On market
Date entered into DSLD Feb 23, 2022
DSLD ID 266790
Product type Amino Acid/protein
Supplement form Tablet Or Pill
Dietary claims / uses Nutrient, All Other, Structure/Function
Intended target group(s) Vegan, Vegetarian, Adult (18 - 50 Years), Kosher, Halal, 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 Double Strength L-Lysine 1000 mg by NOW, 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
733739001139
IngredientAmount% DV
L-Lysine1 Gram(s)--
L-Lysine Hydrochloride1270 mg--

Other ingredients: Microcrystalline Cellulose, Silicon Dioxide, Stearic Acid, Vegetarian Coating, Croscarmellose Sodium, Magnesium 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: Take 1 tablet 1 to 2 times daily.

Formula

Lysine is an essential amino acid that must be obtained through the diet or through supplementation. Lysine is necessary for the production of all proteins in the body, and is required for the maintenance of the structural proteins collagen and elastin, which form all connective tissues such as skin, tendon, and bone. Lysine is also a precursor to carnitine, which is needed for fat metabolism and energy production. In addition, Lysine may help to support a healthy immune system and proper cardiovascular function.

Crescent H (Halal)

Essential Amino Acid

Triangle K (Kosher)

Amino Acids

This product has twice the L-Lysine (1,000 mg per tablet) as in our regular strength product (500 mg per tablet). NOW L-Lysine is a Pharmaceutical Grade essential amino acid.

FDA Disclaimer Statement

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

Precautions

Caution: For adults only.

Consult physician if pregnant/nursing, taking medication, or have a medical condition.

Keep out of reach of children.

Not manufactured with wheat, gluten, soy, milk, egg, fish, shellfish or tree nut ingredients. Produced in a GMP facility that processes other ingredients containing these allergens.

Formulation

Natural color variation may occur in this product.

Supports Collagen Synthesis Healthy Immune Function

Non-GMO

Vegetarian/Vegan

Made and quality tested in the USA with globally sourced ingredients.

Not manufactured with wheat, gluten, soy, milk, egg, fish, shellfish or tree nut ingredients.

Storage

Store in a cool, dry place after opening.

Seals/Symbols

Crescent H (Halal) GMP Quality Assured

Triangle K (Kosher)

FDA Statement of Identity

A Dietary Supplement

General Statements

Family owned since 1968.

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

See for yourself

Double Strength L-Lysine 1000 mg by NOW label

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

Double Strength L-Lysine 1000 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 Double Strength L-Lysine 1000 mg by NOW

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.

L-Lysine

Interacts with
1 drug
1 Gram(s) per serving

Lysine is an essential amino acid your body cannot make on its own, so it must come from food or supplements. People most often take extra lysine to t...

L-Lysine monograph & interactions

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

Interaction report

Double Strength L-Lysine 1000 mg by NOW Drug Interactions

Want to check YOUR meds against Double Strength L-Lysine 1000 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
1Drugs
1 Minor

Ingredients driving the most interactions

L-Lysine 1

Individual Drug Interactions

The ingredients in Double Strength L-Lysine 1000 mg interact with 1 drug. Click any drug to see the details.

1 of the 1 ingredient in Double Strength L-Lysine 1000 mg interact with drugs. Each result below shows which ingredient is responsible. L-Lysine

Each ingredient & the kinds of drugs it affects

For each ingredient in Double Strength L-Lysine 1000 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-Lysine1 drug type · 1 drug

5-Ht4 Agonists

Theoretically, lysine may reduce the effects of 5-HT4 agonists.
Animal research suggests that L-lysine is a partial serotonin receptor 4 (5-HT4) antagonist and inhibits diarrhea induced by the 5-HT4 agonist, 5-hydroxytryptophane.

Likelihood Unlikely Evidence D
L-Lysine full monograph & interactions
The maker

Brand information

Manufacturer and brand details for Double Strength L-Lysine 1000 mg, from the product label.

NOW

See all NOW products
Name
NOW Foods
Street Address
395 S. Glen Ellyn Rd.
City
Bloomingdale
State
IL
ZipCode
60108
Web Address
nowfoods.com
Pharmacist Counseling Corner

Double Strength L-Lysine 1000 mg by NOW: Common Questions

Does Double Strength L-Lysine 1000 mg by NOW interact with any medications?
Yes. Based on its ingredients, Double Strength L-Lysine 1000 mg has a known interaction with 1 medication. Use the checker to see how it interacts with a specific drug.
How can one product interact with so many drugs?
Double Strength L-Lysine 1000 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 L-lysine actually help my cold sores?
Lysine is possibly effective for cold sores, which means there's some evidence it may help, but it's not a guarantee. The proof isn't rock-solid, so it's worth trying if you want, but manage your expectations.
Can I take this while I'm pregnant?
There isn't enough reliable information on lysine supplements in pregnancy to say it's safe or unsafe. Lysine from food is fine, but for supplement use, talk with your doctor or pharmacist first — they know your pregnancy details and can give you personalized advice.
What side effects might I get?
The most common ones are stomach upset, diarrhea, and indigestion. Most people tolerate it well at normal doses, but high amounts are more likely to cause digestive trouble. If you notice these symptoms, lower the dose or stop and check with your pharmacist.
Is this just one ingredient?
Yes — the active ingredient is L-lysine hydrochloride at 1,000 mg. The rest is the tablet coating and fillers to hold it together.
Can I take this while breastfeeding?
There isn't enough reliable data on lysine supplements while breastfeeding, so caution is advised. Talk with your doctor or pharmacist before starting to make sure it's right for you and your baby.

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

Not sure if Double Strength L-Lysine 1000 mg is safe with your meds?

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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.

Double Strength L-Lysine 1000 mg label
Go deeper

The Full Monographs Behind Double Strength L-Lysine 1000 mg’s Ingredients

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

Herb & supplement monograph

Lysine

Interacts with 1 drug

Lysine is an essential amino acid your body cannot make on its own, so it must come from food or supplements. People most often take extra lysine to try to prevent or shorten cold sores, but...

Read the full Lysine monograph →
Sources

Sources & How We Checked

Double Strength L-Lysine 1000 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.

Lysine 7 references
  1. Thein DJ, Hurt WC. Lysine as a prophylactic agent in the treatment of recurrent herpes simplex labialis. Oral Surg Oral Med Oral Pathol 1984;58:659-66. PubMed
  2. McCune MA, Perry HO, Muller SA, O'Fallon WM. Treatment of recurrent herpes simplex infections with L-lysine monohydrochloride. Cutis 1984;34:366-73.
  3. DiGiovanna JJ, Blank H. Failure of lysine in frequently recurrent herpes simplex infection. Treatment and prophylaxis. Arch Dermatol 1984;120:48-51. DOI
  4. Milman N, Scheibel J, Jessen O. Lysine prophylaxis in recurrent herpes simplex labialis: a double-blind, controlled crossover study. Acta Derm Venereol 1980;60:85-7.
  5. Griffith RS, Walsh DE, Myrmel KH, et al. Success of L-lysine therapy in frequently recurrent herpes simplex infection. Treatment and prophylaxis. Dermatologica 1987;175:183-90. DOI
  6. Lo JC, Chertow GM, Rennke H, Seifter JL. Fanconi's syndrome and tubulointerstitial nephritis in association with L-lysine ingestion. Am J Kidney Dis 1996;28:614-7. PubMed
  7. Smriga M, Torii K. L-Lysine acts like a partial serotonin receptor 4 antagonist and inhibits serotonin-mediated intestinal pathologies and anxiety in rats. Proc Natl Acad Sci U S A. 2003 Dec 23;100(26):15370-5.

See these in context on the Lysine 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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