Enhanced antioxidant protection
Supports glutathione production for cellular protection
L-Cysteine
Semi-essential sulfur amino acid crucial for antioxidant production, detoxification, and protein structure
Scientific nameL-Cysteine
FormulaC3H7NO2S
Molecular weight121.16 g/mol
CAS52-90-4
60
absorption score
7
safety / 10
20
USD per month
5
documented interactions
Check it against something
L-Cysteine with:
- Amylase
- Ashwagandha
- Avocado Oil
- BCAA (Branched-Chain Amino Acids)
- Beetroot Powder
- Beta-Alanine
- Bifidobacterium lactis
- Bifidobacterium longum
- Bovine Collagen
- Caffeine
- Calcium
- Calcium Bone Formula
- Calcium Carbonate
- Casein Protein
- Chicken Collagen
- Choline (Bitartrate)
- Chondroitin Sulfate
- Coconut Oil
- Collagen Peptides
- Comprehensive Immune Support Complex
- Comprehensive Multivitamin-Mineral Complex
- Creatine HCL
- Creatine Monohydrate
- D-Mannose
- DHA
- Electrolyte Blend
- EPA
- Fish Oil (EPA/DHA)
- Folate (5-MTHF)
- Ginger
- Iron Fumarate
- Iron Sulfate
- Joint Mobility Formula
- Keratin
- Krill Oil
- L-Carnitine
- L-Citrulline
- Lactase
- Lactobacillus acidophilus
- Lactobacillus rhamnosus
- Lipase
- Magnesium Citrate
- Magnesium Glycinate
- Magnesium Oxide
- Marine Collagen
- Melatonin
- Modafinil
- Olive Oil Extract
- Omega-3 + Curcumin + Vitamin D Triple Anti-Inflammatory Formula
- Papain
- Protease
- Saccharomyces boulardii
- Turmeric
- Vitamin B12 (Cyanocobalamin)
- Vitamin B12 (Methylcobalamin)
- Vitamin C (Ascorbic Acid)
- Vitamin C (Sodium Ascorbate)
- Vitamin D3
- Whey Protein
- Zinc Gluconate
Nothing found
82
out of 100
Works better together
Compatible. Timing differs, so follow each supplement's own window.
What it does
mechanism and evidence for each claimImproved detoxification capacity
Supports liver detoxification and toxin elimination
Enhanced hair, skin, and nail health
Supports healthy keratin production and structural integrity
Respiratory health support
May help reduce mucus thickness and improve breathing
Heavy metal chelation
Helps remove heavy metals and toxic substances
Others take these for the same thing
Same goal, different mechanism — check any of them against this one
Turmeric
Anti-inflammatory & antioxidant
300-1000mg
A
3%
Glutathione
Master antioxidant & detox support
250-750mg
B
20%
Astaxanthin
Superior antioxidant & skin protection
4-12mg
B
20%
SAM-e
Mood support & liver health
400-800mg
A
70%
Plant Collagen
Vegan collagen support & antioxidants
2-5g
C
70%
Quercetin
Immune support & allergy relief
500-1000mg
B
5%
Every pair we checked
12 combinations scored by the engine
L-Cysteine + Caffeine
No documented interaction either way
No known interaction
70
L-Cysteine + Creatine Monohydrate
No documented interaction either way
No known interaction
70
L-Cysteine + Calcium Carbonate
No documented interaction either way
No known interaction
70
L-Cysteine + Whey Protein
No documented interaction either way
No known interaction
70
L-Cysteine + Lactase
No documented interaction either way
No known interaction
70
L-Cysteine + Bovine Collagen
No documented interaction either way
No known interaction
70
L-Cysteine + DHA
No documented interaction either way
No known interaction
70
L-Cysteine + Turmeric
No documented interaction either way
No known interaction
70
L-Cysteine + Fish Oil (EPA/DHA)
No documented interaction either way
No known interaction
70
L-Cysteine + Vitamin D3
Protects cysteine from oxidation and enhances glutathione
Works better together
82
L-Cysteine + Selenium (Thyroid Support)
Essential for glutathione peroxidase function
Works better together
82
L-Cysteine + Glycine
Other amino acids needed for glutathione synthesis
Works better together
82
Dosage
Daily500-1500mg
Antioxidant support500-1500mg daily
Detoxification600-1800mg daily
Hair skin support500-1000mg daily
Upper limit3g daily (with adequate hydration)
Before you take it
VeganYes
When to expect it
First Effects1-2 weeks for antioxidant and detox benefits
Peak Benefits6-12 weeks for sustained cellular protection benefits
Deficiency DevelopmentWeeks during stress, illness, or inadequate methionine
Toxicity OnsetRare, mainly kidney stone risk with very high doses
How to measure it
MarkerPlasma cysteine, glutathione, or oxidative stress markers
OptimalCysteine: 200-350 μmol/L, Glutathione: 900-1400 μmol/L
Deficient belowCysteine: <150 μmol/L
FrequencyEvery 3-6 months if monitoring antioxidant status
What people actually reported to the FDA
CAERS, 11 reports naming it as the suspectMost reported effects
Named as the suspect
11 reports
of 16 that mention it at all
Serious outcome
95%
hospitalisation, emergency room or worse
Other Serious or Important Medical Event8
Visited Emergency Room5
Hospitalization4
Reports are voluntary and unverified — they record what someone experienced while taking something, not what the compound caused. Counts skew towards products people take a lot of, and a serious outcome is more likely to be reported than a mild one, so these are not rates. How we filter them →
What actually reaches you
The label counts the carrier, your body does not
Absorption
High 60 of 100 · absorbs well relative to other forms
Delivered daily
600 mg
Cost per 100 mg delivered
$0.11 comparative — uses the absorption score, not a measured percentage
Works better with
+
Vitamin C
Protects cysteine from oxidation and enhances glutathione
Antioxidant protection and glutathione recycling · level A
+
Selenium
Essential for glutathione peroxidase function
Required cofactor for glutathione enzyme system · level A
+
Glycine Glutamate
Other amino acids needed for glutathione synthesis
Complete glutathione synthesis requires all three amino acids · level AWhat not to take with L-Cysteine
!
Alcohol
Alcohol depletes cysteine and glutathione
Increases oxidative stress and depletes antioxidants · major significance
!
Acetaminophen
Acetaminophen depletes glutathione
Drug metabolism consumes glutathione stores · major significanceMedication interactions
Discuss these with a pharmacist before combiningMay enhance nitrate tolerance
What to do: May help prevent nitrate tolerance
Protective against acetaminophen toxicity
What to do: May help prevent liver damage
Available forms
L-Cysteine (Free Form): Glutathione precursor, Detox support, Hair/skin health, Well-researched
Food sources
Poultry and meat
0.2-0.4g per 100g · 60
Fish and seafood
0.2-0.3g per 100g · 60
Dairy products
0.1-0.2g per 100g · 55
Eggs
0.3g per 100g · 65
Too little
- Reduced glutathione levels and oxidative stress
- Poor detoxification capacity
- Hair loss and brittle nails
- Slow wound healing
- Increased susceptibility to toxins
- Poor immune function
- Respiratory issues with thick mucus
Too much
- Rare with oral supplementation:
- Kidney stone formation (cysteine stones)
- Gastrointestinal upset
- Sulfur intolerance symptoms
- Generally good safety profile
Who benefits most
antioxidant-support
Essential for glutathione production and cellular protection
500-1500mg daily
liver-detox-support
Supports liver detoxification and toxin elimination
600-1800mg daily
hair-skin-nail-health
Provides sulfur for keratin and structural proteins
500-1000mg daily
respiratory-health
May help reduce mucus thickness and improve breathing
600-1200mg daily
heavy-metal-detox
Helps chelate and remove heavy metals
500-1500mg dailyWhere to buy it
Look for L-Cysteine at 500-1500mg per serving. The form that matters here is L-Cysteine (Free Form).
Find on Amazon
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What else affects it
Beyond other supplements
!
Alcohol
Alcohol depletes cysteine and glutathione
Increases oxidative stress and depletes antioxidantsHow it works
- Rate-limiting precursor for glutathione synthesis
- Provides sulfur for disulfide bond formation in proteins
- Essential for phase II liver detoxification pathways
- Chelates heavy metals through sulfur-metal binding
- Breaks disulfide bonds in mucus proteins
- Important for keratin synthesis in hair, skin, and nails
Key findings
what the evidence supports- Essential rate-limiting precursor for glutathione synthesis
- Effective for liver detoxification and antioxidant support
- Important for hair, skin, and nail health
- NAC form generally preferred for better stability and absorption
Sources: NIH Examine.com · data reviewed 2026-08-02
Compiled by Denis, who maintains this database and holds no medical qualification — every figure here is sourced or derived, never asserted. How we calculate it →
Common questions
What are the benefits of L-Cysteine?
Documented effects: Enhanced antioxidant protection; Improved detoxification capacity; Enhanced hair, skin, and nail health; Respiratory health support. Supports glutathione production for cellular protection
How much L-Cysteine should you take per day?
The common daily range is 500-1500mg. By goal — antioxidant support: 500-1500mg daily; detoxification: 600-1800mg daily; hair skin support: 500-1000mg daily; upper limit: 3g daily (with adequate hydration).
When is the best time to take L-Cysteine?
Empty stomach. First effects are typically reported within 1-2 weeks for antioxidant and detox benefits.
What are the side effects of L-Cysteine?
At excessive doses: Rare with oral supplementation:, Kidney stone formation (cysteine stones), Gastrointestinal upset, Sulfur intolerance symptoms, Generally good safety profile. Safety rating at normal doses is 7 out of 10.
What should you not take with L-Cysteine?
Separate it from Alcohol, Acetaminophen by two to four hours. Alcohol depletes cysteine and glutathione
Does L-Cysteine interact with medications?
Documented interactions with nitroglycerin, acetaminophen. Discuss these with a pharmacist before combining.
How do you know if you need L-Cysteine?
The marker is Plasma cysteine, glutathione, or oxidative stress markers, optimal range Cysteine: 200-350 μmol/L, Glutathione: 900-1400 μmol/L. Common deficiency signs: Reduced glutathione levels and oxidative stress, Poor detoxification capacity, Hair loss and brittle nails, Slow wound healing.