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
Highest-scored catalog products containing L-Cystine, ranked by our scoring engine.
Browse all L-Cystine products →
More in Amino Acid
Other ingredients in the Amino Acid category.
5-HTP
Direct serotonin precursor, one step closer than tryptophan. More potent for mood and appetite but requires more caution.
Glycine
Simplest amino acid with diverse roles in collagen synthesis, sleep quality, neurotransmission, and detoxification.
Glycine (for Relaxation)
Simplest amino acid with profound calming and sleep effects. Lowers body temperature.
Glycine (Longevity Dose)
Simplest amino acid with emerging longevity benefits at higher doses. Supports glutathione, collagen, sleep, and may mimic methionine restriction.
Hydrolyzed Whey Protein
Pre-digested whey protein with faster absorption than isolate or concentrate, ideal for post-workout recovery and those with digestive sensitivities.
L Carnitine
L-carnitine is a naturally occurring compound synthesized from amino acids that plays a crucial role in transporting long-chain fatty acids into mitochondria for energy production. Evidence supports modest benefits for exercise performance and recovery in carnitine-deficient individuals, though benefits in healthy populations are limited.
Last reviewed: June 2026 by the Formulate Research Team. Sources cited above; methodology and scoring criteria published here.
Cite this page
Formulate Research Team. (2026, June). 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.