Trends in the Top-Cited Articles on Classic Psychedelics

This review paper (2021) investigates the trends in the top-cited papers on psychedelics and finds more RCT studies on psilocybin being done that get cited more often.

Abstract

“This study was designed to identify trends in the top-cited classic psychedelic publications. The top 50 publications on classic psychedelics with the greatest total of number of citations and annual citation rate were identified and pooled. Unique articles (n = 77) were dichotomized by median year of publication (2010); the differential distribution of study characteristics between the “Recent Cohort” (n = 40) and “Older Cohort” (n = 37) were documented. The Recent Cohort had a greater annual citation rate (median 76.5, IQR 43.8 to 103.3) compared to the Older Cohort (median 8.8, IQR 4.2 to 17.2, p < .001). The Recent Cohort included a greater number of clinical studies (n = 27 [67.5%] vs. n = 10 [27.0%]) while the Older Cohort included more basic science and preclinical studies (n = 22 [59.5%] vs. n = 3 [7.5%], p < .001). Psilocybin was the predominant psychedelic studied in the Recent Cohort (n = 26 [40.6%] vs. n = 8 [17.4%]) while lysergic acid diethylamide (LSD) was predominantly studied in the Older Cohort (n = 26 [56.5%] vs. n = 19 [29.7%], p = .028). The Recent Cohort included more studies examining affective disorders (n = 16 [25.8%] vs. n = 1 [2.7%]) and substance use disorders (n = 6 [9.7%] vs. n = 1 [2.7%]), while the Older Cohort included a greater number of pharmacological outcomes (n = 26 [70.3%] vs. n = 11 [17.7%], p < .001). This study identified and documented trends in the top-cited classic psychedelic publications. The field is continuing to form a foundational understanding of the pharmacological effects of psychedelics and is now advancing with the identification of therapeutic uses within clinical populations.“

Authors: David W. Lawrence, Bhanu Sharma, Roland R. Griffiths & Robin L. Carhart-Harris

Summary

This study identified and documented trends in the top-cited classic psychedelic publications. The Recent Cohort had a greater annual citation rate, included more clinical studies, and examined more affective disorders and substance use disorders than the Older Cohort.

Introduction

The renewed interest in classic psychedelics is evident, and the research documenting a largely therapeutic role for these substances in the treatment of a multitude of mental health-related conditions is expanding.

Psychedelics are a broad class of psychoactive agents that induce alterations in perception, mood, cognition, sense of self, and consciousness. They can be classified by their pharmacodynamics and molecular structure, subjective perceptual, psychological, and/or spiritual effect, and derived source material.

Bibliometric analyses can be used to identify areas that are well established and those that are deficient in the field of psychedelic research. Moreover, publication citation rates act as a proxy for the relative influence of articles within a particular field.

Search strategies and database construction

Two databases were used for the analyses: PubMed and Web of Science. Psilocybin, psilocin, LSD, mescaline, and DMT were included as classic psychedelics, and 2,5-dimethoxy-4-iodoamphetamine was excluded due to its previous recognition within the amphetamine-derivate class.

A search strategy was applied to Web of Science and PubMed to construct a comprehensive database of published works investigating classic psychedelics. The search strategy excluded the terms hallucinogen, LSD, and DMT.

A Web of Science search strategy was completed to identify 8074 relevant articles. A citation report was created with the results and an average citation per year was estimated.

The primary database was rank ordered and sorted by descending order with respect to both total number of citations and annual citation rate. 50 articles were then identified and reviewed for inclusion/exclusion criteria.

Publications investigating or discussing classic psychedelics that were peer-reviewed and the full-manuscript was accessible were included in this study.

Qualitative analyses

Two reviewers independently coded the study design and study outcome(s) for each publication in both cohorts, and consensus was achieved after category development for each MU.

Analysis by year of publication

In order to evaluate trends in publications on the top-cited classic psychedelics by year of publication, two cohorts were created: the Recent Cohort and the Older Cohort.

Descriptive statistics were used to describe the distribution of variables among the two cohorts, and a Wilcoxon Rank Sum test and Fisher test were used to compare the two cohorts.

Results

A total of 8,889 publications were identified on classic psychedelics based on the PubMed search strategy. The annual publication rate increased from 2010 to 2020.

The bibliometric search strategies resulted in two cohorts of 50 publications: the TNC cohort and the ACR cohort. The 50 articles within each cohort underwent full manuscript review.

Trends by year of publication

Twenty-three studies were included in both TNC and ACR cohorts, with 40 studies published within or after 2010 and 37 studies published prior to 2010. The Recent Cohort had a significantly higher annual citation rate than the Older Cohort.

The distribution of country of origin was different between the Recent and Older Cohorts. In the Older Cohort, 78.4% of the studies were conducted in the United States of America.

Study design, psychedelics studied, and study outcomes

The Recent Cohort included a greater number of clinical studies and fewer preclinical studies compared to the Older Cohort, and Psilocybin was the most frequently included psychedelic within the Recent Cohort.

A significant difference was observed in the distribution of study outcomes between the Recent Cohort and Older Cohort. The Recent Cohort included a greater number of studies investigating the therapeutic effect of classic psychedelics, predominantly affective disorders, anxiety, and/or depression, and substance use disorders.

Discussion

This study identified the most cited publications within the field of classic psychedelic research. The most frequently studied psychedelic was psilocybin in the Recent Cohort, while LSD was most frequently studied in the Older Cohort.

The trend toward renewed academic productivity with increasing annual publication rates observed from 2010 through 2020 is consistent with a similar investigation by Rucker and colleagues.

The Recent Cohort of psychedelic research publications supports the sentiment that the field of classic psychedelic research is expanding, with an increasing focus on the clinical use.

The Older Cohort included more preclinical studies, predominantly within animal and in vitro models, whereas the Recent Cohort had a greater number of clinical studies examining psychiatric outcomes. This trend is consistent with other fields of study and follows the process of pharmaceutical development. The field of classic psychedelic research differs from the development of most pharmaceuticals, in that most research has relied on largely nonindustry funded research support.

The field of classic psychedelics is notable, but large clinical trials are resource intensive and are hindered by strict regulatory statutes.

This study was unable to detect potential highly influential novel studies, and highly cited studies that met citation thresholds after the search date were not included. Additionally, the risk of bias and formal analyses of study quality were not conducted.

The field of psychedelics is relatively small, with few active research centers, and may be biased by self-citation rates and excluding non-English manuscripts. Alternative citation indices, such as the g-index, h-index, and e-index, are recognized, but were not incorporated in this study.

This study examined the top-cited classic psychedelic publications and observed that the field continues to explore the physiological and pharmacological effects of psychedelics in preclinical basic science and animal models.