Effect of SSRIs on Response to Psilocybin Therapy

This study is an open-label, single-arm, within-subjects design in individuals with mild-moderate Major Depressive Disorder (MDD). All participants will receive a single dose of 25mg of psilocybin in a therapeutic setting. In order to investigate the effects of length of time on SSRI therapy, 30 participants with varying lengths of time on SSRI therapy will be enrolled, stratified into four groups: * Group 1: ≤ 1 year * Group 2: 1 to ≤ 5 years * Group 3: 5 to ≤ 10 years * Group 4: \> 10 years