Objectives: The studies described in this dissertation aimed to create and validate a standardized questionnaire for the assessment of attitudes about psychedelics, to apply this questionnaire by assessing a group of European psychiatrists about their attitudes, and to complement these findings by conducting selected interviews with European psychiatrists on the same topic. Methods: The first and second studies were cross-sectional and used an online survey. The third study was a qualitative study, based on a reflective thematic analysis of semi-structured interviews. Results: The first research showed the validity of the new instrument and provided preliminary data on the attitudes of the Croatian general population about psychedelics, where it was shown that many people do not even have basic knowledge about psychedelics. The second study showed that European psychiatrists are open to psychedelics, but are concerned about the possible side effects and abuse of these substances. More positive attitudes in that group were associated with previous personal use of psychedelics, greater knowledge about psychedelics, younger age, male gender, and spirituality. Variables related to professional training and practice did not show a significant influence on attitudes on psychedelics. The third study showed the complexity of attitudes on psychedelics and their deep connection to the social, political and historical context. Attitudes on psychedelics in psychiatry are mixed and a large number of psychiatrists believe that the evidence for their therapeutic effectiveness is still not sufficiently convincing. Conclusions: The new instrument we validated has a many potential uses for future research. General knowledge about psychedelics is poor, and psychiatrists state that this topic is underrepresented in their education. This should be improved in order to hold high-quality informed discussions about the future of psychedelic therapy. Our findings suggest that psychedelics are a topic where it is difficult to remain impartial, especially as an education or treatment provider.