L-Cystine
Amino Acid
Also known as: Cystine, L-Cystine
B
Grade B💊 500-1500 mg daily🎯 5 primary uses🔗 3 synergies⚠️ Review warnings
Levels upFitness+50 pts
Overview
Oxidized dimer form of cysteine, important for keratin production, hair/nail/skin health, and antioxidant support via glutathione synthesis.
Primary Uses
Hair healthNail strengthSkin supportKeratin synthesisGlutathione precursor
Frequently Asked About L-Cystine
How much L-Cystine should I take?
The typical effective range is 500-1500 mg daily. Individual needs vary based on age, body weight, diet, and goals — start at the lower end and adjust based on response. Always consult a healthcare provider before starting a new supplement.
When is the best time to take L-Cystine?
With meals. Consistency matters more than perfect timing — pick a daily anchor (e.g. with breakfast or before bed) and stick with it.
Should I take L-Cystine with food?
Best with food.
Does L-Cystine interact with medications?
Yes — known interactions include None significant. If you take any prescription medication, talk to your doctor or pharmacist before starting L-Cystine.
What does L-Cystine pair well with?
L-Cystine stacks well with B vitamins, Biotin, and Other amino acids — these combinations either improve absorption or work synergistically toward common goals.
Who should not take L-Cystine?
L-Cystine should be avoided or used with caution by people with Cystinuria. Pregnant or breastfeeding women should consult a healthcare provider before use.
What are the side effects of L-Cystine?
Most people tolerate L-Cystine well. The most commonly reported side effects are Well tolerated. Side effects are usually dose-dependent — lowering the dose often resolves them.
Dosage
Typical range
500-1500 mg daily
Timing
With meals
With food
Best with food
Duration
Safe long-term
Special Populations
Hair/nail support
Research & Studies
Search the literature now
We haven’t curated landmark studies for L-Cystineyet — one-click into the primary literature here. PubMed (RCTs) is usually the highest-signal starting point.
Mechanism of Action
- • Reduced to cysteine in the body
- • Provides sulfur for keratin production
- • Supports glutathione synthesis
- • Structural component of hair and nails
Evidence Quality
Evidence Grade B
Established role in keratin synthesis and sulfur metabolism
Safety & Contraindications
Serious Warnings
- • None at normal doses
Contraindications
- • Cystinuria
Common Side Effects
- • Well tolerated
Pregnancy & Breastfeeding
Consult healthcare provider
Liver & Kidney Notes
Caution in cystinuria
Interactions
💊 Medications
- • None significant
🧪 Supplements
- • Part of amino acid formulas
🍽️ Food & Alcohol
- • Found in protein foods
Stacking & Synergies
Pairs Well With
Avoid Combining With
None
Best Goal Synergies
Hair growthNail strength
Buying Guide
What to Look For
- • Pure L-cystine
Standardization Markers
L-form specified
Adulteration risk
Low
Practical Notes
- • Often combined with methionine for hair formulas
- • NAC is more bioavailable for glutathione
Tags
amino acidhairnailsskinantioxidant
Top Products with L-Cystine
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Last reviewed: August 2026 by the Formulate Research Team. Sources cited above; methodology and scoring criteria published here.
Cite this page
Formulate Research Team. (2026, August). L-Cystine — Evidence-Based Supplement Guide. Formulate Supplement Encyclopedia. https://app.formulate-health.app/learning/supplements/l-cystine
Educational content based on published research and our scoring methodology. Not medical advice — consult a qualified healthcare provider before starting, stopping, or changing supplements, especially if you take medications, are pregnant, or have a medical condition.