The Psychedelic Renaissance in Clinical Research: A Bibliometric Analysis of Three Decades of Human Studies with Classical Psychedelics

The investigators searched the Web of Science Core Collection on 20 December 2020 using a pre‑specified set of terms targeting classical 5‑HT2A receptor agonists plus MDMA. Search terms included specific drug names (psilocybin, lysergic acid diethylamide/LSD, ayahuasca, N,N‑Dimethyltryptamine, 3,4‑methylenedioxymethamphetamine/MDMA, mescaline, peyote, 5‑MeO‑DMT) and a wildcard Psychedelic*. The time span sampled was 1990–2020 and all available citation indexes within WoS were used (SCI‑Expanded, SSCI, A&HCI, ESCI). The initial search returned 11,921 records. The set was restricted to articles and reviews; other document types (for example, meeting abstracts and letters) were excluded. Results were sorted by citation count (highest first) and the most cited 750 titles were manually screened by two researchers. Screening removed irrelevant records arising from dual‑meaning acronyms (for example, LSD used in non‑psychedelic contexts) and excluded non‑human studies, studies not directly investigating psychedelics’ effects on human brain, behaviour, cognition, emotion or therapeutic efficacy, and research on non‑clinical contexts such as chronic substance use disorders. Discrepancies between reviewers were resolved with a third independent reviewer. From this filtered set the top 100 cited articles (T100) were selected and metadata were extracted from WoS, including year, authorship, affiliations, country, journal, citation data, keywords and funding. Journal impact factors were taken from Journal Citation Reports. The primary author was defined as the first listed author and country/institutional counts were based on affiliations as presented in each publication; when multiple affiliations were listed they were counted individually. Bibliometric analyses and visualisations were performed using bibliometrix, an R‑based scientometrics package. The annual citation rate (ACR) was calculated as total citations divided by years since publication (citations per year = total citations / [2021 − publication year]) to account for exposure time. Co‑citation and co‑occurrence methods were used to map intellectual structure, while co‑authorship analyses mapped collaboration networks. Country‑level productivity was also adjusted using UNESCO GDP/R&D data to produce a GDP‑corrected measure of contribution. Where the extracted text referenced figures, tables or supplementary material for flowcharts and matrices, those items were noted but not reproduced in the extracted text.

The top 100 most cited human psychedelic articles (T100) published between 1990 and 2020 were identified and characterised across several bibliometric dimensions. Citation counts for the T100 ranged from 82 to 668 citations, with a median of 125 and a mean of 158.1 citations. The 15 most‑cited articles accounted for over 30% of total citations within the T100; the three single most cited papers together accumulated 1,491 citations. Re‑ranking by annual citation rate (ACR) altered relative standing of some articles: ACR values in the T100 ranged from 4.1 to 55 citations per year, with a median ACR of 13.1 and a mean of 16.9, and a paper previously ranked seventh by total citations moved to first by ACR. Publication timing showed a pronounced recent rise: 54% of the T100 were published in the most recent decade covered (2010–2019). By five‑year intervals the distribution was 11 articles in the first decade, 35 in the second, and 54 in the last decade. A statistically significant effect of publication year on ACR was reported comparing the first and second halves of the sampled period (t(98) = 4.72, p < .00001), consistent with accelerating impact in recent years. Journals contributing most T100 articles were Journal of Psychopharmacology (18 articles) and Psychopharmacology (12 articles), together providing 30% of the T100. Other generalist high‑impact outlets (for example Biological Psychiatry and PLoS One, as reported) contributed substantially to the field’s global visibility. Author‑level metrics showed Vollenweider FX as the most prolific within the T100 (n = 24 articles), with Carhart‑Harris RL, Nutt D, and Liechti ME together second (n = 11). Vollenweider also had the highest total citations within the T100 (3,646), followed by Griffiths RR (1,887). Local citation analyses (citations within the T100 collection) and temporal production plots were used to characterise influence and activity over time. Collaboration and co‑citation maps identified key author clusters. Country analyses based on corresponding author affiliation indicated that the USA (n = 31), Switzerland (n = 28), the UK (n = 14), Spain (n = 8), and Germany (n = 7) were leading sources of T100 articles. Single‑country publications dominated for the USA (30/32) and Switzerland (24/28), whereas other countries had ≥40% of articles arising from international collaborations. After adjusting for GDP/R&D spending the UK emerged as the most prominent contributor, followed by the USA, Spain and Switzerland. A collaboration map (reported but not reproduced here) depicted international co‑authorship patterns and highlighted major bilateral and multilateral links. Institutional representation showed the University of Zurich and Zurich University Hospital with the highest number of author affiliations in the T100 (n = 32). The analysis also identified two non‑university organisations among the top contributors: the Beckley Foundation (n = 11) and the Multidisciplinary Association for Psychedelic Studies (reported as n = 5 in the extracted text). Of the T100 articles, 88 were original research and 12 were reviews. Co‑citation and collaboration network analyses revealed four principal collaboration clusters led, respectively, by Vollenweider and Liechti; Nutt and Carhart‑Harris; Griffiths and Johnson; and the late Riba. The authors reported that these clusters reflect concentrated hubs of expertise that have shaped the field’s development.

Hadar and colleagues interpreted their findings as quantitative evidence of a ‘‘psychedelic renaissance’’ in human clinical research, marked by both increased production and rising intellectual influence since the turn of the century. The disproportionate concentration of top‑cited articles in the most recent decade was emphasised as corroborating this resurgence. Journal‑level patterns were consistent with Bradford’s law of scattering: a small set of specialised psychopharmacology journals (Journal of Psychopharmacology and Psychopharmacology) account for a large fraction of core publications, while broader high‑impact journals contribute to the field’s visibility and cross‑disciplinary reach. Geographically, the authors highlighted an unusual distribution compared with many medical fields: leading contributions came from the UK, USA, Spain, Brazil and Switzerland. When corrected for national R&D spending, the UK surpassed the USA. Possible contextual explanations proposed by the authors included local traditions of psychedelic use (for example in Brazil) and relatively permissive regulatory environments (for example in Switzerland) that may facilitate clinical research. Institutional network analysis identified Imperial College London, University of Zurich, Johns Hopkins University, Autonomous University of Barcelona and the Federal University of Rio Grande do Norte as prominent centres. The study drew attention to diversity concerns. The bibliometric evidence was presented as consistent with prior reports of participant samples being predominantly White; the authors argued that the investigator pool also appears to be concentrated among researchers from Western, Educated, Industrialized, Rich, and Democratic (WEIRD) contexts. Brazil was noted as a partial exception, but the extracted data did not robustly demonstrate within‑country ethnic diversity of participants. The authors suggested that limited researcher and participant diversity could have implications for culturally appropriate applications of set and setting in psychedelic therapy and for equitable access to emerging treatments. Several limitations were acknowledged. The analysis relied solely on Web of Science; other databases (Scopus, PubMed/Medline, Google Scholar) may yield different citation counts and coverage, particularly for more recent literature. The authors also excluded animal, molecular and cellular studies as well as non‑peer‑reviewed altmetric sources; this narrow scope was justified as focusing on human clinical research but was admitted to create gaps in co‑citation networks that reflect foundational preclinical work. Definitions of ‘‘psychedelics’’ were constrained to a set of commonly studied compounds (MDMA, LSD, psilocybin, ayahuasca) and thus excluded other substances with psychedelic‑like properties. Finally, the authors noted that citation metrics are influenced by publication age and by broader disciplinary citation practices, which limit some interpretations of influence. Concluding their discussion, the investigators described this work as the first scientometric characterisation of clinical psychedelic research in humans across three decades. They presented the mapped networks, influential authors, institutions and journals as a practical resource for clinicians, researchers and policymakers navigating a rapidly evolving field, while recommending broader and more inclusive research practices and further bibliometric work that includes preclinical and non‑clinical literatures.