Methods: In all, 44 psychedelic-naïve participants enrolled in the double-blind, placebo-controlled single ascending dose study (1–12 mg BPL-003). Concentrations of 5-MeO-DMT and its pharmacologically active metabolite, bufotenine, were determined in plasma and urine. PD endpoints included subjective drug intensity (SDI) rating, the Mystical Experience Questionnaire (MEQ-30) and the Ego Dissolution Inventory (EDI). Results: BPL-003 was well tolerated at doses up to 12 mg. There were no serious adverse events (AEs), and most AEs were mild; the most common being nasal discomfort, nausea, headache and vomiting. 5-MeO-DMT was rapidly absorbed and eliminated; the median time to peak plasma concentration was approximately 8–10 min and the mean terminal elimination half-life was <27 min. 5-MeO-DMT systemic exposure increased approximately dose-proportionally, while plasma bufotenine concentrations and urinary excretion of 5MeO-DMT and bufotenine were negligible. The intensity of the SDI ratings was associated with plasma 5MeO-DMT concentrations. MEQ-30 and EDI scores generally increased with the BPL-003 dose; 60% of participants had a ‘complete mystical experience’ at 10 and 12 mg doses. Profound and highly emotional consciousness-altering e!ects were observed with BPL-003, with a rapid onset and short-lasting duration. Conclusion: The novel intranasal formulation of BPL-003 was well tolerated with dose-proportional increases in PK and PD e!ects. The short duration of action and induction of mystical experiences suggest clinical potential, warranting further trials.