Drug and Alcohol Dependence 62 (2001) 215–223 Psychometric assessment of the Hallucinogen Rating Scale  Jordi Riba a , Antoni Rodrı ´guez-Fornells a,b , Rick J. Strassman c , Manel J. Barbanoj a, * a A ` rea d’Inestigacio ´ Farmacolo `gica, Institut de Recerca, Hospital de Sant Pau (HSCSP), Sant Antoni M. Claret, 167, 08025 Barcelona, Spain ; Departament de Farmacologia i Terape `utica, Uniersitat Auto `noma de Barcelona, Spain b Departament de Personalitat, Aaluacio ´ i Tractaments Psicolo `gics, Facultat de Psicologia, Uniersitat de Barcelona, Barcelona, Spain c Taos, NM 87571, USA Received 14 March 2000; received in revised form 13 June 2000; accepted 20 June 2000 Abstract Reliability and convergent-discriminant validity of a Spanish version of the Hallucinogen Rating Scale (HRS) were assessed in two differentiated populations of hallucinogen users involving the retrospective assessment of drug effects. In Study 1 (immediate assessment), 75 European users of the South American hallucinogenic drink ayahuasca answered the HRS 4 h after drug intake in their habitual setting. In Study 2 (delayed assessment), 56 adult polydrug users answered the HRS and a short form of the Addiction Research Center Inventory (ARCI) recalling the effects they experienced when they last took a hallucinogen, in order to test the convergent-discriminant validity of HRS with the scales of the standard questionnaire used in most studies involving psychoactive drugs. The HRS scales showed increases after both the immediate and delayed retrospective assessment of drug effects. Reliability data indicated that four of the six scales show an acceptable level of internal consistency. Significant but limited correlations were found between the Perception and Somaesthesia scales and the ARCI LSD scale, pointing out the question- naire’s construct validity. Thus, the HRS was sensitive to hallucinogenic drug effects other than those elicited by intravenous N,N-dimethyltryptamine (DMT), for which it was originally designed, and showed reasonable reliability and convergent validity. Results suggest its usefulness in the evaluation of subjective effects elicited by psychoactive drugs with hallucinogenic properties, and constitute a preliminary approach to the effects of ayahuasca in European subjects. © 2001 Elsevier Science Ireland Ltd. All rights reserved. Keywords: Hallucinogen Rating Scale (HRS); Immediate versus delayed retrospective assessment; Subjective effects; Reliability; Convergent analysis www.elsevier.com/locate/drugalcdep 1. Introduction Experimental studies involving hallucinogenic drug administration to human subjects have awakened re- newed interest since the research of Hermle et al. (1992) and Vollenweider et al. (1997a,b,c) with model psy- choses in Europe and Strassman’s studies involving the administration of N,N -dimethyltryptamine (DMT) to healthy volunteers in the US (Strassman et al., 1994, 1996; Strassman, 1996). Before the resumption of clini- cal studies, these intriguing drugs had received little attention in psychiatry and human experimental psy- chopharmacology in the last two decades, despite their popularity as recreational drugs. Hallucinogen con- sumption, especially of LSD, rather than decreasing, has remained stable or even increased throughout the years and has recently won new impetus in the form of synthetic amphetamine derivatives such as MDMA (Pope et al., 1990; Schuster et al., 1998). Additionally, in Europe, a new pattern of use is emerging involving the so-called ‘natural drugs’ or ‘shamanic inebriants’, such as peyote (a mescaline-containing cactus) or ayahuasca (a DMT containing-drink) rediscovered by religious cults or ‘new age’ groups. Regarding ayahuasca, several groups ingesting this South Ameri- can hallucinogenic drink have settled in recent years in several European countries, particularly in Holland, Italy, Germany and Spain. This hallucinogenic bever- age is obtained from infusing various plants native to the Amazon Basin, habitually Banisteriopsis caapi and  The full text of Appendix A is available at the journal website at http://www.elsevier.com/locate/drugalcdep under ‘Supplementary Materials’. * Corresponding author. Tel.: +34-93-2919019; fax: +34-93- 2919286. E-mail address: mbarbano@santpau.es (M.J. Barbanoj). 0376-8716/01/$ - see front matter © 2001 Elsevier Science Ireland Ltd. All rights reserved. PII:S0376-8716(00)00175-7