Psilocybin and Affective Function in Chronic Lower Back Pain Depression

This study seeks to provide insight on psilocybin's effects on mechanisms of chronic pain among patients with co-morbid chronic low back pain and depression (CLBP+D). Participants will receive either a single high-dose of psilocybin (25mg absolute dose) or methylphenidate (40mg absolute dose). Participants will be asked to complete assessments of pain, depressive symptoms, and more general questionnaires regarding the participants experiences during the experimental sessions and the associated enduring effects. This study will investigate the effects of a single experimental psilocybin (25 mg fixed dose) administration compared to a dose of methylphenidate (40 mg fixed dose). Assessments will be conducted during screening visits, before and after the drug session, at follow up visits up to 1-month after the drug session, as well as periodically throughout study participation via a multi-time-per-day survey application. Forty participants will complete all study visits including follow-up visits. Primary objectives: 1. Investigate the feasibility, safety, and acceptability of psilocybin for CLBP+D2. Investigate the effect of psilocybin on self-report of positive affect, negative affect, and pain catastrophizing 3. Investigate the effect of psilocybin on a behavioral task called positive affective pain inhibition Secondary objectives: 1. Investigate the durability (1-month follow-up) effects of psilocybin on self-report of positive affect, negative affect, and pain catastrophizing 2. Investigate the effect of psilocybin on dynamic associations between affective measures, pain, and function on a moment-to-moment basis.