Despite growing evidence supporting the efficacy of LSD-assisted psychotherapy in treating major depressive disorder (MDD), identifying reliable psychopharmacological biomarkers remains necessary. Oxytocin, a neuropeptide implicated in social bonding and flexibility, is a promising candidate due to its release following serotonergic psychedelic administration in healthy individuals; however, its dynamics in psychiatric populations are currently unexplored. This observational pilot study aimed to characterize salivary oxytocin dynamics during a single LSD-assisted psychotherapy session in our patients with treatment-resistant MDD. Participants received 100 or 150 µg LSD, and salivary oxytocin was measured at baseline, 60, 90, and 180 min post-LSD. Concurrently, participants rated subjective drug intensity (0–10 scale) at 60, 90, and 180 min. A linear mixed model revealed significant variation of oxytocin levels over time. Perceived psychedelic intensity also significantly varied over time. This supports oxytocin as a potential biomarker. Larger, controlled trials are warranted to replicate these findings and clarify the mechanistic links between oxytocin dynamics and clinical outcomes, including changes in depressive symptoms and mental flexibility.