Double-blind randomized parallel-group trial of adjunctive nitrous oxide (50% N2O/50% O2, 60 min twice weekly for 4 weeks; n=12) vs placebo (100% O2, same schedule; n=11) added to stable SSRI treatment in MDD patients aged 18–65 with HDRS-17 > 17. Primary outcome: HDRS-17 change from baseline. Sponsor: Hospital das Clínicas FMRP-USP, Ribeirão Preto, Brazil.
50% nitrous oxide diluted in 50% oxygen inhaled for 60 minutes twice a week for 4 weeks
50% N2O diluted in 50% oxygen; administered via disposable nasal mask
100% oxygen inhaled for 60 minutes twice a week for 4 weeks
100% oxygen used as placebo