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Dietary supplement

L-Cysteine 500 mg Ingredients & Drug Interactions

by Douglas Laboratories

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

First and foremost: checking L-Cysteine 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: Moderate

L-Cysteine 500 mg is a dietary supplement by Douglas Laboratories with 1 active ingredient. Its ingredients are commonly taken for antioxidant support, skin and hair health, liver support.Based on those ingredients, 86 medications have a known interaction with it, the most serious rated moderate. The ingredients most likely to interact are L-Cysteine. 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-Cysteine 500 mg by Douglas Laboratories

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

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HelloPharmacist Scorecard of L-Cysteine 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-cysteine, a semi-essential amino acid your body uses to build and repair tissue. The capsule also holds cellulose, gelatin, and vegetable stearate as inactive ingredients to hold everything together.

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 L-cysteine product and its label doesn't state a use — see L-cysteine'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-cysteine doesn't currently support using it for androgenic alopecia (pattern hair loss), venous leg ulcers, hangover, stroke, or gastritis. The data we hold rates all of these as having insufficient reliable evidence.

That doesn't mean it doesn't work — it means the quality or size of existing studies isn't strong enough to confirm a benefit.

The evidence, ingredient by ingredient L-cysteine

How safe is it?

Some data gaps
Safety Information · database check
Some gaps

Safety data exists for these ingredients, but with some important gaps.

Why this rating?
  • We hold adverse-effect (side-effect) data for 0 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-cysteine from food sources is generally well tolerated. However, the safety of high-dose supplements like this one over the long term hasn't been well studied.

The dose in this product is above what you'd get from a normal diet, so use it cautiously and only if your doctor advises it. For pregnancy and lactation, L-cysteine is rated as likely safe, though supplement-level doses haven't been extensively studied — talk with your doctor or pharmacist about whether it's right for you during these times.

Side effects, ingredient by ingredient L-cysteine

Meds to double-check

Moderate interaction found
Known Interaction Concern · database check
Moderate identified

The most serious documented interaction for these ingredients is Moderate. Check your medications for a personalized result.

Why this rating?
  • 1 of the 1 matched ingredient can interact with medications — L-cysteine.
  • The most serious interaction on file is rated Moderate.
  • Some involve high-stakes drug classes: diabetes medications.
  • For scale: 86 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 antidiabetes drugs (insulin, metformin, sulfonylureas, or other blood-sugar-lowering medications), check your exact prescriptions with the tool on this page before adding L-cysteine, as it may increase the risk of low blood sugar.

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. Moderate medication interactions have been identified, and some safety-information gaps remain.

This product is a simple, single-ingredient amino acid supplement. If you take diabetes medication, you'll want to clear it with your doctor or pharmacist first because of the low blood sugar risk.

Since high-dose safety data is limited, it's wise to use it only if your healthcare provider recommends it.

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 1, 2012.

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-Cysteine 500 mg, straight from the product label.

Brand Douglas Laboratories
Barcode (UPC) 310539002681
Net contents 60 Capsule(s)
Market status On market
Date entered into DSLD Jun 1, 2012
DSLD ID 8699
Product type Amino Acid/protein
Supplement form Capsule
Dietary claims / uses All Other
Intended target group(s) Adult (18 - 50 Years), 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 L-Cysteine 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
310539002681
IngredientAmount% DV
L-Cysteine500 mg--

Other ingredients: Cellulose, Gelatin, 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.
Formulation

This product contains NO yeast, wheat gluten, soy protein, milk/dairy, corn, sodium, sugar, starch, artificial coloring, preservatives or flavoring.

Storage

For optimal storage conditions, store in a cool, dry place. (59(0)-77(0)F/15(0)-25(0)C) (35-65% relative humidity)

Precautions

Tamper resistant package, do not use if outer seal is missing.

KEEP OUT OF REACH OF CHILDREN.

General

Formula #7433

Suggested/Recommended/Usage/Directions

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

FDA Statement of Identity

A Dietary Supplement

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

See for yourself

L-Cysteine 500 mg by Douglas Laboratories label

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

L-Cysteine 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-Cysteine 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-Cysteine

Interacts with
86 drugs
500 mg per serving

L-cysteine is a sulfur-containing amino acid your body uses to make proteins and the antioxidant glutathione. Most people get enough from food, and su...

L-Cysteine monograph & interactions

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

Interaction report

L-Cysteine 500 mg by Douglas Laboratories Drug Interactions

Want to check YOUR meds against L-Cysteine 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
86Drugs
86 Moderate

Ingredients driving the most interactions

L-Cysteine 86

Individual Drug Interactions

The ingredients in L-Cysteine 500 mg interact with 86 drugs. Click any drug to see the details.

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

Each ingredient & the kinds of drugs it affects

For each ingredient in L-Cysteine 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-Cysteine1 drug type · 86 drugs

Antidiabetes Drugs

Theoretically, taking L-cysteine supplements with antidiabetes drugs might increase the risk of hypoglycemia.
Animal research suggests that L-cysteine can have hypoglycemic effects.

Likelihood Possible Evidence D
L-Cysteine full monograph & interactions
The maker

Brand information

Manufacturer and brand details for L-Cysteine 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
Web Address
www.douglaslabs.com
Pharmacist Counseling Corner

L-Cysteine 500 mg by Douglas Laboratories: Common Questions

Does L-Cysteine 500 mg by Douglas Laboratories interact with any medications?
Yes. Based on its ingredients, L-Cysteine 500 mg has a known interaction with 86 medications. Use the checker to see how it interacts with a specific drug.
How can one product interact with so many drugs?
L-Cysteine 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.
Is L-cysteine safe to take while pregnant or breastfeeding?
L-cysteine is rated as likely safe during pregnancy and lactation. That said, supplement-level doses haven't been extensively studied in these situations, so talk with your doctor or pharmacist about whether it makes sense for your personal situation.
Does this supplement have any reported side effects?
No adverse effects are documented in the data we hold for L-cysteine. That doesn't mean none can occur, but none have been flagged in the available evidence.
Can L-cysteine help with hair loss?
The evidence for L-cysteine and androgenic alopecia (pattern hair loss) is insufficient to say whether it works. The studies available aren't strong enough to confirm a benefit.
Is this product free of fillers?
No — this capsule contains cellulose, gelatin, and vegetable stearate as inactive ingredients to hold the L-cysteine in form. These are standard binders and capsule materials.
How much L-cysteine is too much?
Food amounts of L-cysteine are generally well tolerated. This supplement provides a dose higher than you'd get from diet, and the long-term safety of high-dose supplements hasn't been well studied. Use it only if your doctor advises, and ask them about what amount makes sense for you.

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

Not sure if L-Cysteine 500 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.

L-Cysteine 500 mg label
Go deeper

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

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

Herb & supplement monograph

L-cysteine

Interacts with 86 drugs

L-cysteine is a sulfur-containing amino acid your body uses to make proteins and the antioxidant glutathione. Most people get enough from food, and supplements are usually well tolerated, bu...

Read the full L-cysteine monograph →
Sources

Sources & How We Checked

L-Cysteine 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 2 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.

L-cysteine 2 references
  1. Dowlati Y, Maheux M, Meyer JH. The effect of oral L-cysteine on breast milk and plasma cysteine concentrations. Neuropsychiatr Dis Treat 2020;16:3163-3172.
  2. Lee S, Han KH, Nakamura Y, et al. Dietary L-cysteine improves the antioxidative potential and lipid metabolism in rats fed a normal diet. Biosci Biotechnol Biochem 2013;77(7):1430-4.

See these in context on the L-cysteine 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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