The PASSENGER project aims to conduct a pilot feasibility study of the implementation of a randomized clinical trial on psilocybin-assisted psychotherapy for the treatment of gambling disorder. Feasibility will be assessed by estimating the ability to retain participants until the end of the protocol. Other objectives of the study will be to generate preliminary efficacy data, identify clinical factors potentially associated with the intensity of the psychedelic experience (which determines the expected therapeutic effect), and conduct a preliminary assessment of the safety of the treatment under study.