Molecular hydrogen (H2) appeared as an experimental agent in biomedicine approximately 40 years ago, yet the past 5 years seem to confirm its medicinal value in the clinical environment. H2 improves clinical end-points and surrogate markers in several clinical trials, from metabolic diseases to chronic systemic inflammatory disorders to cancer. However, less information is available concerning its medicinal properties, such as dosage and administration, or adverse reactions and use in specific populations. The present paper overviews the clinical relevance of molecular hydrogen, and summarizes data from clinical trials on this innovative medical agent. Clinical profiles of H2 provide evidence-based direction for practical application and future research on molecular hydrogen for the wider health care community.