Sustained Mood Improvement with Laughing Gas Exposure (SMILE): Study protocol for a randomized placebo-controlled pilot trial of nitrous oxide for treatment-resistant depression. - Ladha KS; Lee J; Mattina GF; Pazmino-Canizares J; Wijeysundera DN; Gholamali Nezhad F; Philip K; Tassone VK; Adamsahib F; Bhat V (PloS one, 2024)