tuneTypical Dose
600-1200
Supplement
L-cysteine
L-cysteine
Evidence TierCWADA PROHIBITED
watchEffect Window
Next-day hangover period
lockCompliance
WADA PROHIBITED
Overview
Clinical Summary
L-cysteine is an amino acid or related metabolite involved in protein turnover and cellular signaling. It is taken to support exercise performance, recovery, or specific metabolic pathways.
Evidence is context dependent. Trials most often evaluate exercise outcomes such as fatigue, blood flow, or muscle soreness, and some show small benefits at adequate doses. Minority uses include support for wound healing, immune function, and sleep quality. Effects vary with baseline protein intake, training status, and coingested nutrients.
Likely supports acetaldehyde-related and redox pathways, but clinical effect consistency is limited.
Outcomes
What This Is Expected To Influence
Primary Outcomes
- Possible reduction in selected hangover symptoms
- Low-certainty evidence overall
Secondary Outcomes
- Formulation-specific effects likely
- Not a broad alcohol-harm solution
Safety
Contraindications and Interactions
Contraindications
- Pregnancy/lactation
- Severe liver disease without supervision
- Alcohol use disorder without formal care
Side effects
- Possible GI upset
- Persistent hangover symptoms despite use
- Uncertain benefit consistency
Interactions
- Multi-ingredient hangover products (confounding)
- Complex polypharmacy (caution)
- Overlapping antioxidant stacks
Avoid if
- Under legal drinking age
- Escalating harmful drinking behavior
- Inability to track symptom response
Evidence
Study-level References
l-cysteine-SRC-001Randomized double-blind placebo-controlled trial
Sourceopen_in_newEriksson CJP, et al. L-Cysteine containing vitamin supplement and alcohol-related hangover symptoms. Alcohol Alcohol. 2020;55(6):660-666. PMID:32808029
Population: Healthy adult men (n=19), high alcohol challenge
Dose protocol: 600 or 1200 mg L-cysteine formulation
Key findings: Reduced selected hangover symptoms
Notes: Small sample and specific cohort
Paper content
Reduced selected hangover symptoms
l-cysteine-SRC-002Systematic review
Sourceopen_in_newRoberts E, et al. Pharmacologically active interventions for alcohol-induced hangover: systematic review of RCTs. Addiction. 2022;117(8):2157-2167. PMID:34972259
Population: 21 RCTs, 386 participants total
Dose protocol: Heterogeneous interventions (including L-cysteine)
Key findings: No high-certainty recommendation for any intervention
Notes: Very low certainty for efficacy outcomes
Paper content
No high-certainty recommendation for any intervention
l-cysteine-SRC-003Randomized double-blind crossover placebo-controlled trial
Sourceopen_in_newCoppersmith V, et al. N-acetylcysteine in prevention of hangover: randomized trial. Sci Rep. 2021;11(1):13397. PMID:34183702
Population: Healthy volunteers (n=49)
Dose protocol: NAC 600-1800 mg around alcohol challenge
Key findings: No overall significant total-score benefit
Notes: Related compound (NAC), overall null primary result
Paper content
No overall significant total-score benefit
l-cysteine-SRC-004Randomized, placebo-controlled trial.
Sourceopen_in_newKumar P, Liu C, Suliburk J, et al. Supplementing Glycine and N-Acetylcysteine (GlyNAC) in Older Adults Improves Glutathione Deficiency, Oxidative Stress, Mitochondrial Dysfunction, Inflammation, Physical Function, and Aging Hallmarks. J Gerontol A Biol Sci Med Sci. 2023;78(1):75-89. doi:10.1093/gerona/glac135. PMID:35975308.
Population: Older adults compared with young adult controls.
Dose protocol: GlyNAC (glycine plus NAC) for 16 weeks versus alanine placebo in older adults.
Key findings: Corrected glutathione deficiency, improved oxidative stress, mitochondrial function, inflammation, and physical function. Supports cysteine-availability as rate-limiting for glutathione synthesis in aging.
Notes: Uses NAC (cysteine prodrug) rather than free L-cysteine. Small sample (n=24 older adults). Single-center design.
Paper content
This RCT tested GlyNAC (glycine plus N-acetylcysteine, a cysteine prodrug) versus alanine placebo for 16 weeks in 24 older adults, with 12 young adults as a comparison group. GlyNAC supplementation corrected glutathione deficiency, improved oxidative stress, mitochondrial dysfunction, inflammation, and physical function measures. While the intervention uses NAC rather than free L-cysteine, it supports the broader rationale that cysteine availability is rate-limiting for glutathione synthesis in aging. The small sample size and single-center design limit generalizability, but the breadth of improved endpoints is notable.
l-cysteine-SRC-005Randomized, double-blind, parallel-group, benchmark- and placebo-controlled trial.
Sourceopen_in_newDuperray J, Sergheraert R, Chalothorn K, Tachalerdmanee P, Perin F. The effects of the oral supplementation of L-Cystine associated with reduced L-Glutathione-GSH on human skin pigmentation: a randomized, double-blinded, benchmark- and placebo-controlled clinical trial. J Cosmet Dermatol. 2022;21(2):802-813. doi:10.1111/jocd.14137. PMID:33834608.
Population: Asian female subjects.
Dose protocol: 500 mg L-cystine with or without 250 mg reduced glutathione versus placebo for 12 weeks.
Key findings: L-cystine plus glutathione produced significant skin lightening and dark spot reduction at 12 weeks in Asian women. L-cystine alone showed a weaker signal.
Notes: Cosmetic endpoint limits health relevance. Four-arm design with 124 participants is the largest direct L-cystine human trial.
Paper content
This four-arm RCT tested L-cystine (500 mg) with and without reduced glutathione (250 mg) versus glutathione alone and placebo for 12 weeks in 124 Asian women. The combination group showed significant skin lightening and facial dark spot reduction at 12 weeks. L-cystine alone showed a weaker signal. The study supports L-cystine's role in modulating melanin synthesis through glutathione-dependent pathways, though the cosmetic endpoint limits clinical health relevance. This is the strongest direct evidence for standalone L-cystine supplementation producing a measurable human outcome.