L-Cysteine HCl
Also known as: L-Cysteine Hydrochloride, L-Cys, Cysteine HCl, L-cysteine.HCl.H2O
Effective Dosage
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, one of its main antioxidant compounds. The strongest human evidence comes from a 3-year placebo-controlled trial in patients with erythropoietic protoporphyria — a rare genetic disorder causing extreme light sensitivity — where 500 mg per day significantly increased the time patients could tolerate sunlight without symptoms. Animal studies suggest it may help the body handle certain heavy metal exposures, such as cobalt and cadmium, though results were mixed and human data is absent.
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. No evidence it protects against electromagnetic radiation from phones — that transdermal patch study was a formulation experiment, not a clinical outcome trial. Don't expect anti-aging, immune, or muscle-building benefits based on the available data.
Evidence-Based Benefits
L-Cysteine HCl is the hydrochloride salt form of cysteine, a sulfur-containing amino acid your body uses to make glutathione, one of its main antioxidant compounds. The strongest human evidence comes from a 3-year placebo-controlled trial in patients with erythropoietic protoporphyria — a rare genetic disorder causing extreme light sensitivity — where 500 mg per day significantly increased the time patients could tolerate sunlight without symptoms. Animal studies suggest it may help the body handle certain heavy metal exposures, such as cobalt and cadmium, though results were mixed and human data is absent.
Weak EvidenceEffective at: 500-1000 mg/day based on limited clinical data
Source: auto-research
Absorption & Bioavailability
Unknown from provided studies. The parenteral nutrition research confirms stability in IV solutions, but oral bioavailability data was not covered in the provided papers.
Red Flags to Watch For
- Only one small human clinical trial in the provided evidence, and it was for a rare genetic disease — results may not apply to healthy people
- Potential interaction with copper in nutritional formulations; copper levels can drop when L-Cysteine HCl is present
- Animal data showed cysteine supplementation actually increased kidney cadmium accumulation in infected chicks — suggesting detox effects are not straightforward
- Widely marketed as a glutathione booster and general detox agent, but no human trials in the provided data support these broad claims
- Found in over 1,000 registered supplement products despite very limited clinical evidence for most marketed uses
Products Containing L-Cysteine HCl
See how L-Cysteine HCl is used in these analyzed products:
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: 2026-04-09