L-Cysteine
What it is
The conditionally essential amino acid serving as the rate-limiting substrate for glutathione synthesis. While NAC is better absorbed and more studied, L-cysteine offers a cost-effective alternative with comparable antioxidant and hepatoprotective benefits at adequate doses. RCTs at 400–800 mg/day show improvements in hair shaft diameter and tensile strength. Also used in mucolytic and liver-protective protocols. Dietary cysteine often falls short during oxidative stress, illness, or intense training.
Dose
500–1,500 mg/day in divided doses with food
Time of day & tips
Synergistic with glycine (GlyNAC stack); add B6 and zinc to support the transsulfuration pathway; not dose-equivalent to NAC
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