Over the last two decades, in North America and Europe, a growing number of laboratories have initiated clinical studies to evaluate the therapeutic potential of so-called “psychedelic” substances. Once viewed by the medical community as “hallucinogens” with pathogenic properties, these substances are now perceived by many clinicians as the next generation of treatments for mental health disorders. Based on the preliminary results of a survey conducted within clinical research units mobilizing the use of hallucinogens as well as on the analysis of the interplay of social actors involved in the medicalization of psychedelics, this article explores the modalities of this contemporary requalification of hallucinogens, the social dynamics underlying it and their epistemological, political and ethical stakes. The author highlights the central role played by religious organizations in these dynamics as well as the importance of the mobilization of medical authority in the legitimization of these emerging social practices. As some states consider changing the legal status of hallucinogens and as these substances attract the interest of private investors, a growing number of voices are being raised to oppose the medicalization of psychedelics. The reclassification of the status of hallucinogens thus promises to raise strong political, epistemological and ethical tensions. Keywords: hallucinogens – psychedelics – medecine – drugs – religion.