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Dietary supplement

L-Cysteine Powder Ingredients & Drug Interactions

by Source Naturals

L-Cysteine Powder label
See full label image
Powder Category: Amino Acid/protein
Most serious interaction: Moderate
Clinical methodology reviewed by · Updated Sep 16, 2026 · Label data from the NIH DSLD
What is this page for?

First and foremost: checking L-Cysteine Powder 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 Powder is a dietary supplement by Source Naturals 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.

Jump to a section

Check Your Meds Against L-Cysteine Powder by Source Naturals

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

Pharmacist-reviewed data Checks every ingredient Answer in seconds
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HelloPharmacist Scorecard of L-Cysteine Powder by Source Naturals

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 powder contains one active ingredient: L-cysteine, an amino acid your body uses to make glutathione, a key antioxidant. There are no inactive ingredients listed for this product.

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: liver protection and antioxidant support.
  • Our graded evidence for these ingredients doesn't cover that particular purpose.

We don't have solid evidence yet for L-cysteine's effectiveness at any of the conditions it's marketed for — androgenic alopecia (male-pattern hair loss), venous leg ulcers (slow-healing sores in the legs), hangover, stroke, and gastritis. The data we hold rates them all as insufficient evidence to say whether it works.

That doesn't mean it doesn't; it means the studies aren't there yet to prove it does.

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 is generally well tolerated at the amounts found in food, but the long-term safety of high-dose supplements hasn't been well studied. The safety notes advise caution with supplement-level doses unless your doctor recommends otherwise.

Pregnancy and lactation: the data rates L-cysteine as likely safe during pregnancy and breastfeeding, but because high-dose supplement safety overall isn't well established, it's smart to talk with your doctor or pharmacist about whether to take it.

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.

Check your exact antidiabetes medications (insulin, metformin, sulfonylureas, and similar drugs) with your doctor or pharmacist before starting L-Cysteine. The interaction is Moderate severity — it may raise the risk of low blood sugar (hypoglycemia).

No other medication types are documented to interact with L-cysteine in our data.

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.

L-Cysteine may be worth considering if you're curious about amino acid supplements, but the evidence for what it treats isn't solid yet. If you take any blood sugar medication, you'll need to check with your doctor or pharmacist first — there's a real risk it could lower your blood sugar further.

The long-term safety at supplement doses isn't well known, so stick with personalized advice from your healthcare provider.

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 Nov 22, 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 L-Cysteine Powder, straight from the product label.

Brand Source Naturals
Barcode (UPC) 021078001201
Net contents 3.53 Ounce(s); 100 Gram(s)
Market status On market
Date entered into DSLD Nov 22, 2022
DSLD ID 274767
Product type Amino Acid/protein
Supplement form Powder
Dietary claims / uses Nutrient, All Other, Structure/Function
Intended target group(s) Adult (18 - 50 Years), 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 L-Cysteine Powder by Source Naturals, 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:
1.2 Gram(s)
Maximum serving Sizes:
1.2 Gram(s)
Servings per container
83
UPC/BARCODE
021078001201
IngredientAmount% DV
L-Cysteine900 mg--

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.
FDA Statement of Identity

Dietary Supplement

Formula

L-Cysteine is a crystalline free-form amino acid that is active in many body processes. L-Cysteine works in the liver to protect the body from harmful substances and may help to prevent oxidation of tissues. L-Cysteine, along with L-glutamic acid and glycine, is the rate-limiting precursor in the synthesis of glutathione per-oxidase (one of the body's main antioxidant enzymes), which minimizes lipid peroxidation (fats turning rancid).

Suggested/Recommended/Usage/Directions

Suggested Use: 1/4 teaspoon per day between meals. If you experience stomach irritation, take with meals.

Precautions

Note: If you are pregnant, may become pregnant, or are breastfeeding, consult your health care professional before using this product.

Do not use if either tamper-evident seal is broken or missing.

Keep out of the reach of children.

Storage

Store in a cool, dry place.

Formulation

Contains no yeast, dairy, egg, gluten, corn, soy or wheat. Contains no sugar, starch, salt, preservatives, or artificial color, flavor or fragrance.

Free-form

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.

Brand IP Statement(s)

Copyright SOURCE NATURALS, INC.

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

See for yourself

L-Cysteine Powder by Source Naturals label

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

L-Cysteine Powder 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 Powder by Source Naturals

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

Serving size1.2 Gram(s) Dosage formPowder Servings per container83 Amounts shown are per serving.

L-Cysteine

Interacts with
86 drugs
900 mg per serving Form: L-Cysteine Hydrochloride Monohydrate

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
Interaction report

L-Cysteine Powder by Source Naturals Drug Interactions

Want to check YOUR meds against L-Cysteine Powder?

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 Powder interact with 86 drugs. Click any drug to see the details.

1 of the 1 ingredient in L-Cysteine Powder 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 Powder 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 Powder, from the product label.

Source Naturals

Name
Source Naturals, Inc.
Street Address
P. O. Box 2118
City
Santa Cruz
State
CA
ZipCode
95062
Web Address
www.sourcenaturals.com
Pharmacist Counseling Corner

L-Cysteine Powder by Source Naturals: Common Questions

Does L-Cysteine Powder by Source Naturals interact with any medications?
Yes. Based on its ingredients, L-Cysteine Powder 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 Powder 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?
The data we hold rates L-cysteine as likely safe during pregnancy and lactation. That said, because high-dose supplement safety in general isn't well studied over time, talk with your doctor or pharmacist about whether to take it during pregnancy or while breastfeeding.
Does L-Cysteine actually help with hair loss?
We don't have reliable evidence yet to say whether L-cysteine works for androgenic alopecia (male-pattern hair loss). The current data is insufficient to rate it either way.
What does L-cysteine do in the body?
L-cysteine is an amino acid your body uses to make glutathione, a powerful antioxidant. It's naturally present in protein-rich foods.
Are there any side effects listed for L-Cysteine?
No adverse effects are documented in our data for L-cysteine. That said, high-dose supplement safety over time hasn't been well studied, so it's best to stay in touch with your doctor about any changes you notice.
Can I take L-Cysteine if I take diabetes medication?
Not without checking first. Animal research suggests L-cysteine may lower blood sugar, so taking it with your diabetes drug could theoretically increase the risk of low blood sugar. Talk with your doctor or pharmacist before starting — they may want to watch your blood sugar more closely or adjust your dose.
How long has L-Cysteine been studied?
The long-term safety of supplement-level doses isn't well established. Food amounts are considered fine, but we don't have strong data on high-dose supplements taken over time, so caution is advised.

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

Not sure if L-Cysteine Powder 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.

L-Cysteine Powder label
Go deeper

The Full Monographs Behind L-Cysteine Powder’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 Powder'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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