The Afterglow Inventory (AGI) – validation of a new instrument for measuring subacute effects of classic serotonergic psychedelics

Background: Classic psychedelics such as psilocybin and LSD are anecdotally associated with the phenomenon of "psychedelic afterglow," a set of predominantly pleasant, temporary psychological effects reported after the acute effects have subsided. Since post-acute effects are crucial for the therapeutic use of psychedelics, an instrument to systematically assess subacute "afterglow" effects is needed.Aims:To create and validate a questionnaire to quantify subacute "afterglow" effects of psychedelics.Methods: An international online survey was conducted in English and German. Participants who had consumed a psychedelic (N = 1,323) or another non-psychedelic substance (control group, N = 157) within the past four weeks were included. An initial list of 97 items was progressively reduced to 24 items.Results: A 5-factor structure best fit the data and showed high internal consistency. The factors included 1) Vitality, 2) Transpersonal Aspects, 3) Inspiration/Creativity, 4) Interpersonal Relationships, and 5) Relationship to Nature. The final 24-item version of the Afterglow Inventory (AGI) effectively differentiated between the psychedelic group and the control group. The overall AGI score positively correlated with the intensity (r = 0.165; p < 0.001) and positive valence (r = 0.251; p < 0.001) of the acute psychedelic effects.Conclusions: The AGI is a novel scale for quantifying positive subacute ("afterglow") effects of psychedelics. The use of the AGI could lead to a better understanding of the interplay between acute, subacute, and long-term effects of psychedelics. Insights could also be gained into how different substances, dosages, and extra-pharmacological factors, such as psychotherapy, might influence outcomes.