The Hallucinogen Rating Scale: Updated Factor Structure in a Large, Multistudy Sample

The Hallucinogen Rating Scale (HRS) has been widely used to measure the subjective effects of psychedelics and other psychoactive substances. Its advantages include a basis in phenomenological interviews and clinical studies, straightforward items, and broad coverage of psychedelic effects. Previous studies have attempted to resolve its factor structure but were limited by small samples of participants who took only one substance. We obtained 991 HRS questionnaires from the authors of 18 publications involving 13 psychoactive substances. Exploratory factor analysis was used to analyze its factor structure, and mixed-effects analyses of variance were used to compare HRS scores between drugs. The HRS resolved into 8 factors with good to excellent internal consistency and that intuitively map onto the effects of psychedelics. The factor model also showed good measures of fit that were superior to previous proposed models. Model factors were able to show dose responses for most drugs. Additionally, patterns of responses on the 8 factors significantly differentiated classic psychedelics, such as psilocybin and DMT, from other substance classes, including dissociatives such as ketamine and salvinorin A, empathogens such as MDMA, stimulants such as methylphenidate and amphetamine, and Δ9-tetrahydrocannabinol. The factor of meaningfulness also uniquely differentiated psychedelics from all other substances. These data show that the HRS is an intuitive and psychometrically sound tool for measuring the effects of psychedelic drugs, and it may also have utility for measuring the effects of other drugs and altered states of consciousness. Calder et al. have updated the Hallucinogen Rating Scale, a popular instrument for assessing drug-induced altered states of consciousness. They retrieved data from 18 studies and 13 psychoactive substances, including psychedelics, dissociatives, empathogens, and others. Factor analysis revealed 8 intuitive and psychometrically sound factors that improve the questionnaire’s function. These factors can distinguish between doses, and different drug classes show specific patterns of effects. The factor “Meaningfulness” seems to be uniquely sensitive to the effects of psychedelics.