Molecular hydrogen (H2) has been shown to have diverse biomedical effects. As a small molecular gas, hydrogen can be diffused to the target without hindrance. A variety of related hydrogen products used in medical research and public health have been developed. There are various methods of administration of H2, mainly including inhaling hydrogen gas, drinking hydrogen water, injecting hydrogen-saline, orally taking solid-state H2 sustained-release agents, and stimulating intestinal microbiomes to produce hydrogen. Pharmacokinetics of H2 in vivo vary with methods of administration and thus influence its biomedical effects. This review summarizes the types of H2 donors and their pharmacokinetics in vivo.