Definition and research guide
This page combines a MeSH definition, publication statistics and selected research abstracts. It is a starting point for reading the literature, not a medical textbook or a systematic evidence review.
Content available: 3 complete abstracts (505 words), 9 references. Full article text is not stored or reproduced here; follow the PMID, DOI or PMC links to read the original sources and their access terms.
Definition
Drugs capable of inducing illusions, hallucinations, delusions, paranoid ideations, and other alterations of mood and thinking. Despite the name, the feature that distinguishes these agents from other classes of drugs is their capacity to induce states of altered perception, thought, and feeling that are not experienced otherwise.
Definition: NLM Medical Subject Headings (MeSH) scope note (Public domain (U.S. National Library of Medicine); attribution requested). View the MeSH record.
Also known as: Hallucinogen; Hallucinogenic Agent; Agent, Hallucinogenic; Psychedelic Agents; Agents, Psychedelic; Psychotomimetic Agents; Agents, Psychotomimetic; Hallucinogenic Drugs.
Where it fits in the MeSH classification
- Broader topics
- Physiological Effects of Drugs; Psychotropic Drugs
- See also
- Hallucinations
Research landscape
PubMed indexes 9,666 records tagged with the MeSH heading “Hallucinogens” (counts retrieved 2026-10-29). 3,760 of them (38.9%) were published from 2020 onward, and the busiest period so far is 2020 onward with 3,760 records.
Reviews account for 1,747 records (18.1%) and meta-analyses for 93. Randomized controlled trials number 375 (3.9%) as a share of all records on the topic.
Show the data
| Period | Records |
|---|---|
| through 1999 | 2,700 |
| 2000-2009 | 1,621 |
| 2010-2019 | 1,585 |
| 2020 onward | 3,760 |
Publication-type chart data
| Type | Records | Share |
|---|---|---|
| Reviews | 1,747 | 18.1% |
| Meta-analyses | 93 | 1.0% |
| Randomized controlled trials | 375 | 3.9% |
Method: PubMed query "Hallucinogens"[MeSH Terms] with publication-type and date filters, retrieved 2026-10-29.
Reading the evidence in pharmacology
Drug evidence builds in layers: laboratory pharmacology describes how a compound acts, pharmacokinetic studies describe how the body handles it, and randomized trials test whether it helps and what harms it causes. Post-marketing surveillance and observational studies reveal rarer adverse effects but cannot prove causation. This page is educational and is not a recommendation to start, stop or change any medicine; decisions about treatment belong with a qualified clinician.
Evidence from open-access studies
These open-access studies come from PubMed’s best-match results for this heading (papers whose main topic it is), ranked here by citation count, with one recent addition. Each abstract is reproduced in full under its recorded open licence so that you can read the authors’ own words. They illustrate the literature; they are not a systematic summary of it. Citation counts measure attention, not reliability or clinical benefit.
| Study / authors | Year | Source label / design | Europe PMC citations | Licence / source |
|---|---|---|---|---|
| Molecular design of a therapeutic LSD analogue with reduced hallucinogenic potential | 2025 | Research article Design not recorded in structured metadata | 38 | cc by PMID 40228113 · DOI · PMC12037037 |
| An international Delphi consensus for reporting of setting in psychedelic clinical trials | 2025 | Research article Design not recorded in structured metadata | 35 | cc by PMID 40461819 · DOI · PMC12283393 |
| Human brain changes after first psilocybin use | 2026 | Research article Design not recorded in structured metadata | 21 | cc by PMID 42086570 · DOI · PMC13144397 |
Molecular design of a therapeutic LSD analogue with reduced hallucinogenic potential [1]
Abstract reading summary — source excerpts
- Opening excerpt
- Decreased dendritic spine density in the cortex is a key pathological feature of neuropsychiatric diseases including depression, addiction, and schizophrenia (SCZ).
- Closing excerpt
- This work underscores the potential of nonhallucinogenic psychoplastogens for treating diseases where the use of psychedelics presents significant safety concerns.
- Interpretation limits
- Verbatim excerpts from the authors’ abstract; the closing excerpt may describe a finding, limitation or recommendation. Design, population, effect size and uncertainty have not been independently extracted or appraised. Read the complete abstract and linked paper before interpreting the findings.
Read complete abstract (129 words)
Decreased dendritic spine density in the cortex is a key pathological feature of neuropsychiatric diseases including depression, addiction, and schizophrenia (SCZ). Psychedelics possess a remarkable ability to promote cortical neuron growth and increase spine density; however, these compounds are contraindicated for patients with SCZ or a family history of psychosis. Here, we report the molecular design and de novo total synthesis of (+)-JRT, a structural analogue of lysergic acid diethylamide (LSD) with lower hallucinogenic potential and potent neuroplasticity-promoting properties. In addition to promoting spinogenesis in the cortex, (+)-JRT produces therapeutic effects in behavioral assays relevant to depression and cognition without exacerbating behavioral and gene expression signatures relevant to psychosis. This work underscores the potential of nonhallucinogenic psychoplastogens for treating diseases where the use of psychedelics presents significant safety concerns.
Abstract reproduced from the open-access article under the recorded cc by licence; © the authors. PMID 40228113 · DOI · PMC12037037
An international Delphi consensus for reporting of setting in psychedelic clinical trials [2]
Abstract reading summary — source excerpts
- Opening excerpt
- Psychedelic substances exhibit complex interactions with the 'set and setting' of use, that is, the mental state of the user and the environment in which a psychedelic experience takes place.
- Closing excerpt
- The ReSPCT guidelines and accompanying explanatory document provide a new standard for the design and documentation of extra-pharmacological variables in psychedelic clinical research.
- Interpretation limits
- Verbatim excerpts from the authors’ abstract; the closing excerpt may describe a finding, limitation or recommendation. Design, population, effect size and uncertainty have not been independently extracted or appraised. Read the complete abstract and linked paper before interpreting the findings.
Read complete abstract (199 words)
Psychedelic substances exhibit complex interactions with the 'set and setting' of use, that is, the mental state of the user and the environment in which a psychedelic experience takes place. Despite these contextual variables' known importance, psychedelic research has lacked methodological rigor in reporting extra-pharmacological factors. This study aimed to generate consensus-based guidelines for reporting settings in psychedelic clinical research, according to an international group of psychedelic researchers, clinicians and past trial participants. We conducted a Delphi consensus study composed of four iterative rounds of quasi-anonymous online surveys. A total of 89 experts from 17 countries independently listed potentially important psychedelic setting variables. There were 770 responses, synthesized into 49 distinct items that were subsequently rated, debated and refined. The process yielded 30 extra-pharmacological variables reaching predefined consensus ratings:i.e., 'important' or 'very important' for ≥70% of experts. These items compose the Reporting of Setting in Psychedelic Clinical Trials (ReSPCT) guidelines, categorized into physical environment, dosing session procedure, therapeutic framework and protocol, and subjective experiences. Emergent findings reveal significant ambiguities in current conceptualizations of set and setting. The ReSPCT guidelines and accompanying explanatory document provide a new standard for the design and documentation of extra-pharmacological variables in psychedelic clinical research.
Abstract reproduced from the open-access article under the recorded cc by licence; © the authors. PMID 40461819 · DOI · PMC12283393
Human brain changes after first psilocybin use [3]
Abstract reading summary — source excerpts
- Opening excerpt
- Psychedelics have robust effects on acute brain function and long-term behavior but whether they also cause enduring functional and anatomical brain changes is largely unknown.
- Closing excerpt
- All effects are exclusive to 25 mg psilocybin; no effects occur with a 1 mg psilocybin placebo.
- Interpretation limits
- Verbatim excerpts from the authors’ abstract; the closing excerpt may describe a finding, limitation or recommendation. Design, population, effect size and uncertainty have not been independently extracted or appraised. Read the complete abstract and linked paper before interpreting the findings.
Read complete abstract (177 words)
Psychedelics have robust effects on acute brain function and long-term behavior but whether they also cause enduring functional and anatomical brain changes is largely unknown. In an exploratory, placebo-controlled, within-subjects, electroencephalography (EEG), and magnetic resonance imaging (MRI) study in 28 healthy, entirely psychedelic-naive participants, anatomical and functional brain changes are detected from one-hour to one-month after a single high-dose (25 mg) of psilocybin. Increases in cognitive flexibility, psychological insight, and well-being are seen at one-month. Diffusion tensor imaging (DTI) done before and one-month after 25 mg psilocybin reveals decreased axial diffusivity bilaterally in prefrontal-subcortical tracts that correlate with decreases in brain network modularity (fMRI) over the same month. Enduring functional brain changes are largely absent, but network modularity change (numerical decrease) negatively correlates with well-being change (significant increase), in line with previous findings in depression. Increased cortical signal entropy (EEG) at 1- and 2-hours post-dosing predicts improved psychological well-being at one-month. Next-day psychological insight mediates the entropy to well-being relationship. All effects are exclusive to 25 mg psilocybin; no effects occur with a 1 mg psilocybin placebo.
Abstract reproduced from the open-access article under the recorded cc by licence; © the authors. PMID 42086570 · DOI · PMC13144397
Key reviews and meta-analyses
The most cited review-type papers among PubMed’s best-match results for this heading, listed with bibliographic details only. Follow the links for the full text and access terms.
- Research article Validation of the revised Mystical Experience Questionnaire in experimental sessions with psilocybin [4]
- Research article Cessation and reduction in alcohol consumption and misuse after psychedelic use [5]
- Research article Psychiatric symptoms caused by cannabis constituents: a systematic review and meta-analysis [6]
- Research article Adverse Events in Studies of Classic Psychedelics: A Systematic Review and Meta-Analysis [7]
- Research article Psychedelic therapy for depressive symptoms: A systematic review and meta-analysis [8]
- Research article Psilocybin-assisted therapy for depression: A systematic review and meta-analysis [9]
References
- Tuck JR, Dunlap LE, Khatib YA, Hatzipantelis CJ, Weiser Novak S, Rahn RM, et al.. Molecular design of a therapeutic LSD analogue with reduced hallucinogenic potential. . 2025. PMID 40228113 · DOI · PMC12037037
- Pronovost-Morgan C, Greenway KT, Roseman L, ReSPCT Experts. An international Delphi consensus for reporting of setting in psychedelic clinical trials. . 2025. PMID 40461819 · DOI · PMC12283393
- Lyons T, Spriggs M, Kerkelä L, Rosas FE, Roseman L, Mediano PAM, et al.. Human brain changes after first psilocybin use. . 2026. PMID 42086570 · DOI · PMC13144397
- Barrett FS, Johnson MW, Griffiths RR. Validation of the revised Mystical Experience Questionnaire in experimental sessions with psilocybin. J Psychopharmacol. 2015. PMID 26442957 · DOI · PMC5203697
- Garcia-Romeu A, Davis AK, Erowid F, Erowid E, Griffiths RR, Johnson MW. Cessation and reduction in alcohol consumption and misuse after psychedelic use. J Psychopharmacol. 2019. PMID 31084460 · DOI
- Hindley G, Beck K, Borgan F, Ginestet CE, McCutcheon R, Kleinloog D, et al.. Psychiatric symptoms caused by cannabis constituents: a systematic review and meta-analysis. Lancet Psychiatry. 2020. PMID 32197092 · DOI · PMC7738353
- Hinkle JT, Graziosi M, Nayak SM, Yaden DB. Adverse Events in Studies of Classic Psychedelics: A Systematic Review and Meta-Analysis. JAMA Psychiatry. 2024. PMID 39230883 · DOI · PMC11375525
- Ko K, Kopra EI, Cleare AJ, Rucker JJ. Psychedelic therapy for depressive symptoms: A systematic review and meta-analysis. J Affect Disord. 2023. PMID 36209780 · DOI
- Haikazian S, Chen-Li DCJ, Johnson DE, Fancy F, Levinta A, Husain MI, et al.. Psilocybin-assisted therapy for depression: A systematic review and meta-analysis. Psychiatry Res. 2023. PMID 37844352 · DOI
About this article
- Sources
- NLM Medical Subject Headings (definition, synonyms); NCBI PubMed (counts, identifiers); Europe PMC (open-access abstracts and citation counts).
- Verification
- Every reference was resolved against PubMed on 2026-10-31; title, year and DOI matched.
- Review state
- automated source verified; no human expert review has been recorded yet.
- Version
- 1, last updated 2026-10-29.
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Evidence strength
EvidenceHelix's computed view of the study designs behind this topic: how common meta-analyses, randomized trials and reviews are, how recent the literature is, and a plain-language reading. It describes the design mix of the literature. It is not a quality appraisal of any study, and it is not medical advice.