Table 1 Summary of published findings.

Study	n	Condition	N₂O Dose	Control	No. of Sessions	Primary Outcome	Timepoints	% Response in N₂O Group	% Remission in N₂O Group	Group Comparison (N₂O vs placebo)
Guimarães et al. 2021	21^a N₂O = 12 placebo = 9	MDD	50%	100% oxygen	8	HAM-D17	Before and after each session (twice a week for four weeks)	91.7	75	Time-drug interaction^c p < 0.005
Nagele et al. 2015	20^b crossover trial	TRD	50%	50% nitrogen: 50% oxygen	1	HDRS-21	2 h 24 h	20	15	p < 0.001
Nagele et al. 2020	1	MDD	50%	n/a	1	PHQ-9	1 month	n/a	100	n/a
Nagele et al. 2021	24^b crossover trial	TRD	25% and 50%	air/oxygen	2	HDRS-21	2 h 24 h 1 week 2 weeks	41.7 (50%), 33.3 (25%)^d	41.7 (50%), 22.2 (25%)^d	p = 0.01
Yan et al. 2022	42^b N₂O = 20 placebo = 22	TRD	50%	50% air: 50% oxygen	1	HDRS-21	2 h 24 h 1 week 2 weeks	10 (24 h) 10 (1 week) 30 (2 weeks)	0 (24 h) 10 (1 week) 15 (2 weeks)	p = 0.017 (2 h) p = 0.033 (24 h) p = 0.463 (1 week) p = 0.711 (2 weeks)

The bold text shows the sample size and the italics provide additional information about the group allocations.
MDD major depressive disorder, TRD treatment-resistant depression, HAM-D17 17-item Hamilton Depression Rating Scale, HDRS-21 21-item Hamilton Depression Rating Scale, PHQ-9 Patient Health Questionnaire.
^an based on total number of participants who completed the trial.
^bn based on modified intention-to-treat analyses.
^cSignificant group differences observed post-session 4 (p = 0.027), post-session 7 (p = 0.008), pre-session 8 (p = 0.046) and post-session 8 (p = 0.003).
^dThis analysis only included data where pre-treatment HDRS-21 scores were ≥19.

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