When to take it
With food, once a day.
← All supplements
Amino acidsWeak evidence
L-cysteine
Also known as: cysteine
L-cysteine is a sulphur amino acid that the body uses to make glutathione and that builds keratin in hair and nails. You normally get it from dietary protein.
What it is used for
- Hair and nails in combination products – weak evidence
- Glutathione production – weak evidence (NAC is better studied)
- Antioxidant support – weak evidence
Forms and how they differ
L-cysteine
free amino acid, often in hair formulas
NAC (N-acetylcysteine)
more stable and better-studied form
L-cystine
oxidised form, used in hair products
Pairs well with
Works well with vitamin C, zinc and biotin.
Do not combine / separate
Do not stack with NAC and other sulphur amino acids without checking the total dose.
Watch out for
Not recommended in pregnancy or breastfeeding due to lack of data. If you have cystinuria, kidney or liver disease or take medicines, consult your doctor.
Safety
Well tolerated at usual doses; may cause digestive upset. Do not exceed the label dose.
Practical tip
With hair loss, first have your iron, ferritin and thyroid checked.
Products containing L-cysteine 3
Glutathione + L-cysteine + Vitamin Cmixed
L-cysteine
L-cysteine 500 mgfree form · 500 mg / tablet
How to read the evidence rating
Strong evidenceModerate evidenceWeak evidenceNo evidence
Strong = several good human studies or official recommendations; moderate = promising but smaller studies; weak = few studies or mixed results; no evidence = claims not confirmed.
Combination check
Select the supplements you take and, if relevant, your medicines. We show what interferes, what needs a time gap and what to watch out for.
Check L-cysteine with othersWhich supplements do you actually need?
Fénix Methode picks them from your blood results and schedules when to take what – no needless purchases.
From the same group
Acetyl-L-carnitineWeak evidenceAlmond proteinWeak evidenceAmino acid complexWeak evidenceBCAAWeak evidenceBeef proteinModerate evidenceCaseinStrong evidence
Important notice
This information is educational and does not replace advice from a doctor or pharmacist. We do not give medicine dosages. Supplements are no substitute for a varied diet; if pregnant, breastfeeding, ill or on medication, consult a doctor first.