We carried out a randomized, double-blind, placebo-controlled trial of hyperbaric oxygen therapy (HBO) in patients with chronic stable MS. Eighty-two patients were treated in a multiplace hyperbaric chamber with gas supplied by mask. Forty-one patients received 20 consecutive daily treatments of 100% O2 followed by 7 “booster” treatments in the next 6 months; 41 control patients received “air” (12.5% O2 at 1.75 atmospheres absolute). There was no significant difference in treatment and control groups in the Extended Kurtzke Disability scores, Kurtzke Functional scores, magnetic resonance imaging, or evoked potentials after the initial 20 treatments or after the boosters. HBO is not effective in treating chronic stable MS.

Harpur, Suke, Bass, Bass, Bull, Reese, Noseworthy, Rice, (1986). Hyperbaric oxygen therapy in chronic stable multiple sclerosis: double-blind study. Neurology, 1986 Jul;36(7):988-91. https://www.ncbi.nlm.nih.gov/pubmed/3520382