Last verified: 17 days ago
L-Cysteine HCl
Also known as: L-Cysteine Hydrochloride, L-Cys HCl, Cysteine HCl, L-cysteine.HCl.H2O
Evidence under review. — Not yet rated
Amino acid supplement with limited clinical evidence; best studied for a rare light-sensitivity disorder.
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What it does
L-Cysteine HCl is the hydrochloride salt form of cysteine, a sulfur-containing amino acid your body uses to make glutathione, a key antioxidant. The strongest clinical evidence comes from a 3-year...
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Evidence quality
Evidence base hasn't been formally rated yet. See research below.
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Clinical dose
500-1000 mg/day based on limited clinical data
What the Science Says
L-Cysteine HCl is the hydrochloride salt form of cysteine, a sulfur-containing amino acid your body uses to make glutathione, a key antioxidant. The strongest clinical evidence comes from a 3-year placebo-controlled trial showing that 500 mg twice daily significantly increased symptom-free light exposure in people with erythropoietic protoporphyria, a rare genetic disorder causing extreme sun sensitivity. In animal studies, cysteine supplementation helped reduce accumulation of toxic heavy metals like cobalt in liver tissue, though these findings have not been confirmed in humans.
What It Doesn't Do
Not proven to detox your body in any general sense. No human evidence it boosts glutathione levels meaningfully when taken orally as a supplement. No clinical proof it protects against electromagnetic radiation from phones. No evidence it improves skin, hair, or nails in healthy people. The 'antioxidant powerhouse' marketing is not backed by human trials in the provided data.
Evidence-Based Benefits
Increases symptom-free sun exposure time in people with erythropoietic protoporphyria.
Moderate EvidenceEffective at: 500 mg twice daily (1000 mg/day)
Supporting studies (click to view on PubMed):
Reduces cobalt accumulation in liver tissue when dietary cobalt is elevated (animal data only).
Weak EvidenceEffective at: No established human dose
Supporting studies (click to view on PubMed):
Absorption & Bioavailability
Unknown from provided studies — oral bioavailability in humans is not directly assessed in the provided papers. Parenteral (IV) stability data exists for clinical nutrition use.
Red Flags to Watch For
- Most research is in animals (chicks) or highly specialized clinical populations — results may not apply to healthy adults
- Potential interaction with copper in parenteral nutrition solutions; copper binding effects are not fully characterized for oral supplementation
- Transdermal patch formulations for EMF protection have no credible clinical evidence and represent a red flag for pseudoscientific marketing
- Only one small clinical trial (47 patients) supports any human benefit, and it was for a rare genetic disease — not general wellness
Products Containing L-Cysteine HCl
See how L-Cysteine HCl is used in these analyzed products:
Frequently Asked Questions
What does L-Cysteine HCl do?
Amino acid supplement with limited clinical evidence; best studied for a rare light-sensitivity disorder.
What is the effective dose of L-Cysteine HCl?
500-1000 mg/day based on limited clinical data
Is L-Cysteine HCl safe?
Most research is in animals (chicks) or highly specialized clinical populations — results may not apply to healthy adults
What doesn't L-Cysteine HCl do?
Not proven to detox your body in any general sense.
Research Sources
- PubMed
- NIH DSLD
This information is for educational purposes only and is not medical advice. Always consult a healthcare professional before starting any supplement regimen. Last updated: 2026-05-25