Oral glutathione supplements are ineffective, since glutathione is a protein and is digested in the stomach before reaching the blood stream or tissues of the body. Researchers found that 3 grams of glutathione (a whopping dose) taken orally were ineffective in increasing circulating glutathione (glutathione in the bloodstream) in a clinical study evaluating the benefits of oral glutathione. Witschi A, Reddy S, Stofer B, Lauterburg BH. The systemic availability of oral glutathione. (source: Eur J Clin Pharmacol 1992;43(6):667-9)

Intravenous (IV) Glutathione is effective but expensive, uncomfortable, and somewhat impractical requiring infusions 2 times per month (or more) using an Intravenous (IV) line. Glutathione precursors such as n acetyl cysteine (provided by Max GXL) are a better solution for chronic supplementation.
The U.S. Government's Clinical Trials website (www.glinicaltrials.gov) lists numerous clinical trials using IV glutathione or glutathione precursors: clinical trials of glutathione