Human studies used the reduced form (GSH). A label that only says "contains glutathione" does not tell you whether it is oxidised (GSSG) or reduced, and a yeast-extract format does not tell you how many mg of GSH it holds. Look for "reduced" or "L-Glutathione (reduced)" together with the GSH figure in mg.

Evidence:Richie 2015, Eur J Nutr

We cannot say that. A 2012 study reported a lower melanin index at 500 mg over 4 weeks and a 2017 study reported a trend toward better elasticity at 250 mg over 12 weeks, but both were small and short. Glutathione is also not an approved functional ingredient in Korea, so whitening claims or comparisons to injectable procedures are not permitted.

Evidence:Arjinpathana & Asawanonda 2012, J Dermatolog TreatWeschawalit 2017, CCID

Oral glutathione can degrade during digestion, so absorption design matters; a liposomal formulation showed improved absorption (Sinha 2018). Even without it, a product with the reduced form, disclosed content and a named supplier can reach A grade. Also check whether the price is sustainable for 12 weeks or more.

Evidence:Sinha 2018, Eur J Clin Nutr