RESULTS: Drinking high H2 water seems to raise the concentration of H2 more than the H2 saturated (1.6 ppm) water in vivo. Urinary 8-OHdG was significantly reduced by 14.3% (p < 0.01) on average. DAS28 also decreased from 3.83 to 3.02 (p < 0.01) during the same period. After the wash-out period, both the urinary 8-OHdG and the mean DAS28 decreased, compared to the end of the drinking period. During the second drinking period, the mean DAS28 was reduced from 2.83 to 2.26 (p < 0.01). Urinary 8-OHdG was not further reduced but remained below the baseline value. All the 5 patients with early RA (duration < 12 months) who did not show antibodies against cyclic citrullinated peptides (ACPAs) achieved remission, and 4 of them became symptom-free at the end of the study.