Despite suggestive early findings on the therapeutic use of hallucinogens in the treatment of substance use disorders  rigorous follow-up has not been conducted To determine the safety and feasibility of psilocybin as an adjunct to tobacco smoking cessation treatment we conducted an open-label pilot study administering moderate (20 mg/70 kg) and high (30 mg/70 kg) doses of psilocybin within a structured 15-week smoking cessation treatment protocol