|Synopsis: Over 500 peer-reviewed articles show molecular hydrogen (H2 gas) to be therapeutic in 150 different human disease models, and in essentially every organ of the human body. This medical gas has marked therapeutic potential in the field of disease prevention and neuroprotection. H2 can easily diffuse through the blood-brain-barrier, cell membranes and intercellular compartments, not only because it is the smallest molecule in the universe, but it is also electrically neutral and hydrophobic. H2 selectively scavenges the cytotoxic hydroxyl radicals (*OH) without eliminating the beneficial signaling molecules (e.g. H2O2, NO*, O22-, etc.). It can also stimulate the Nrf2 pathway leading to increased endogenous antioxidants including glutathione, superoxide dismutase, catalase, etc. . Lastly, the cell modulating property of H2 affords it with remarkable anti-inflammatory, anti-alleragy, anti-apoptotic, and other neuroprotective benefits.