L-cystine,
does it really help with Improvement in diffuse hair loss and hair growth?
research showsThe 47-person trial combined L-cystine with retinol and gelatin, while the 72-person trial combined it with B vitamins and other ingredients. Every cited human trial tested a combination, and no human hair-loss efficacy trial of L-cystine alone was identified, so the result cannot be attributed to L-cystine. This is an indeterminate rating due to absent single-ingredient human evidence, not a finding of no effect.
ads claimPharmacy hair-nutrition products and direct-import products present “a keratin-building amino acid,” “root nutrition,” “reduced telogen shedding,” and “hair growth.” The public clinical trials concern multi-ingredient medicines or nutritional combinations, not L-cystine capsules alone.
Useful facts when choosing a product
- The key 1989 combination contained L-cystine 70 mg/day, retinol 18,000 IU/day, and gelatin 7 g/day.
- The 1993 trial compared two combinations with different B-vitamin and L-cystine contents.
- Efficacy endpoints included anagen and telogen proportions on trichogram, hair density, and hair swelling.
- The short-term tolerability signal for L-cystine itself was good, but the high-dose vitamin A in the combination has separate safety implications.
What the research actually shows
The 47-person double-blind trial tested L-cystine plus retinol and gelatin, while the 72-person randomized double-blind trial tested L-cystine with B vitamins and other ingredients. Neither included an L-cystine-only arm.
Why this is classified as ?
Every cited human trial tested a combination, with no L-cystine-only arm or standalone efficacy trial. Because ingredient attribution is impossible, no score is assigned and the rating is indeterminate.
Counterpoint. Signals exist for the full formulations, but the single-ingredient contribution is unknown.
Rejudgment record. Reassessment (cross-check reflected) — The only human trials tested a 47-person L-cystine-retinol-gelatin combination and a 72-person combination with B vitamins and other ingredients; no standalone human hair-loss efficacy trial permits attribution to L-cystine, so the rating is indeterminate
Cross-check — Codex and Claude
Evidence Table
| Study | Design | Sample | Funding | Endpoint | Result | Weight |
|---|---|---|---|---|---|---|
| Hertel H et al. 1989 | Pilot clinical study followed by a double-blind placebo-controlled trial | 47 | Unknown | Anagen and telogen proportions on trichogram and hair density | The L-cystine, retinol, and gelatin combination was reported to reduce telogen rate by 13.5% and improve anagen rate by 8%. | Key |
| Budde J et al. 1993 | Randomized, double-blind, placebo-controlled comparative trial | 4 | Included an author affiliated with Agpharm | Hair swelling, frontal/parietal anagen rate, and investigator/participant assessment | Active combination 1 was superior to placebo, and the contribution of additional ingredients was not replaced by higher L-cystine alone. | Key |
Receipt — 2 References
All 2 cited sources were verified for existence at the original page (as of 2026-07-11).
Reviewed and approved: Chamgap Editorial Team · Approval date: 2026-07-11 · Corrections: none
Cite this verdict
[Chamgap] L-cystine x improvement in diffuse hair loss and hair growth — Evidence Grade ?. 2 cited sources checked. Source: https://health-receipt.pages.dev/en/verdicts/skin-hair/l-cystine-diffuse-hair-loss-growth/ · CC BY 4.0CC BY 4.0 — free to use with attribution; do not distort grades, numbers, or verdict meaning.
What this document does and does not do
Chamgap is an information source. It reports what research has and has not confirmed; it does not tell readers what to take or buy. That decision belongs to readers and, when needed, medical or legal professionals. This verdict reflects literature available up to the search date and may change as new research appears. Nothing here is medical advice.