Amino Acid
L-Cystine
Also known as: Cystine, L-Cystine
Oxidized dimer form of cysteine, important for keratin production, hair/nail/skin health, and antioxidant support via glutathione synthesis.
Last reviewed June 2026 · Evidence graded from peer-reviewed research, not editorial opinion. Educational only — not medical advice.
Every L-Cystine product we have scored
| # | Product | Score | Per serving |
|---|---|---|---|
| 1 | Thorne Amino Complex - Travel Packs - Berry | 85 A- | $1.20 |
| 2 | Thorne Amino Complex - Travel Packs - Lemon | 85 A- | $1.20 |
| 3 | Thorne Amino Complex - Berry | 84 A- | $1.47 |
| 4 | Thorne Amino Complex - Lemon | 84 A- | $1.47 |
| 5 | Thorne Amino Complex | 80 A- | $1.20 |
Scored on dose accuracy, form, label transparency and third-party testing. Per-serving cost is list price divided by servings per container. No brand pays to be listed or ranked.
Common questions
How much L-Cystine should I take?
The typical range is 500-1500 mg daily. Safe long-term
When should I take L-Cystine?
With meals. Best with food.
Which form of L-Cystine is best?
Capsule — Common form. Other forms in the catalog: Powder.
Is L-Cystine safe?
Commonly reported: Well tolerated. Serious warnings: None at normal doses. Caution in cystinuria
Which L-Cystine supplement scores highest?
Thorne Amino Complex - Travel Packs - Berry, at 85/100. Scored on dose accuracy, form, label transparency and third-party testing — no brand pays to be listed or ranked.
Primary uses
- Hair health
- Nail strength
- Skin support
- Keratin synthesis
- Glutathione precursor
How it works
- Reduced to cysteine in the body
- Provides sulfur for keratin production
- Supports glutathione synthesis
- Structural component of hair and nails
Dosage
- Typical range
- 500-1500 mg daily
- Timing
- With meals
- With food
- Best with food
- Duration
- Safe long-term
- Special populations
- Hair/nail support
Forms
- Capsule
- Powder
Safety
Common side effects
- Well tolerated
Contraindications
- Cystinuria
Products containing L-Cystine
Top-scoring supplements in our catalog that list L-Cystine on the label. Each product is graded on Formulate's ingredient-level rubric — dose accuracy, form, transparency, and third-party testing.
Evidence notes
Established role in keratin synthesis and sulfur metabolism
Grade B: Some human trials support key claims; further confirmation needed.
Related in Amino Acid
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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.