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Amino Acid

L-Cysteine HCl Anhydrous

Also known as: L-Cysteine Hydrochloride, N-Acetyl-L-Cysteine precursor, Cysteine HCl

B
Evidence

L-Cysteine HCl is a semi-essential amino acid that serves as a precursor to glutathione, a major cellular antioxidant. It plays roles in protein synthesis, detoxification, and hair/skin/nail health.

Last reviewed June 2026 · Evidence graded from peer-reviewed research, not editorial opinion. Educational only — not medical advice.

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Primary uses

  • Glutathione production
  • Antioxidant support
  • Hair, skin, and nail health
  • Detoxification support
  • Immune function

How it works

  • Precursor to glutathione synthesis
  • Disulfide bond formation in proteins
  • Cellular antioxidant defense
  • Chelation of heavy metals

Dosage

Typical range
500-1,500 mg daily
Timing
Any time; may divide doses
With food
Can take with or without food
Duration
Safe for long-term use; effects on antioxidant status build over weeks
Special populations
Individuals with homocystinuria should avoid or use under medical supervision

Forms

  • Powder· 70/100
  • HCl salt· 70/100

Safety

Common side effects

  • Nausea
  • Diarrhea
  • Abdominal discomfort
  • Headache (rare)

Contraindications

  • Homocystinuria (genetic metabolic disorder)
  • Cystinosis
  • Pregnancy and lactation (limited safety data; use only if medically indicated)

Evidence notes

Good evidence for cysteine's role in glutathione synthesis and antioxidant support from mechanistic and clinical studies. RCT evidence exists for specific conditions (acetaminophen toxicity, respiratory health) though most general wellness uses are supported by moderate evidence.

Grade B: Some human trials support key claims; further confirmation needed.

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Medical disclaimer. This page is educational and does not replace advice from a qualified healthcare provider. Individual needs and risks vary — consult a professional before starting, stopping, or combining supplements, especially if you are pregnant or nursing, taking medication, or managing a health condition.