A human clinical trial demonstrated that oral Gamma-glutamylcysteine (GGC) is directly taken up by cells and increases glutathione (GSH) within several hours. This ability to rapidly increase cellular glutathione (GSH), even in healthy subjects, is unlike any other supplement on the market, including glutathione itself. 
Gamma-glutamylcysteine (GGC) has the advantage of being able to diffuse into cells where it is effectively converted to glutathione (GSH) by an enzymatic reaction which simply adds the amino acid glycine. Unlike cysteine prodrugs, such as NAC, which only increase cellular glutathione (GSH) following severe depletion such as in acetaminophen (paracetamol) overdose, gamma-glutamylcysteine (GGC) does so without limitations. This ability to increase glutathione (GSH) regardless of the current state of cellular glutathione (GSH) makes gamma-glutamylcysteine (GGC) unique in the vast supplement market touting effective ways to do so. The body’s biochemistry clearly indicates and research confirms that consuming gamma-glutamylcysteine (GGC) is the only way to ensure healthy glutathione (GSH) levels for all individuals including those suffering from chronic disease and inflammation.
- Zarka, M.H. and W.J. Bridge, Oral administration of γ-glutamylcysteine increases intracellular glutathione levels above homeostasis in a randomised human trial pilot study. Redox Biology, 2017. 11: p. 631-636.