Psychedelics.

MDMA alters several messenger systems, with both reported emotional effects and important bodily risks.

Ideas from Cédric Hysek, Linda Simmler, Yasmin Schmid and colleagues; Christopher Verrico, Gregory Miller and Bertha Madras; NIH NIDA · MDMA transporter research, human social-cognition studies and public health information

Research and institutional explanations are credited in the sources. The lesson, teaching example and diagrams are original simplifications.

Serotonin and noradrenaline release are especially important in MDMA's effects; dopamine also contributes. Noradrenaline is also called norepinephrine. A transporter moves molecules across a cell boundary. A receptor responds to molecular contact by changing cell activity. MDMA mainly changes messenger availability through transporters. Classic psychedelics such as DMT and psilocin prominently activate serotonin receptors.

In a controlled study of 32 healthy volunteers, Hysek and colleagues found increased emotional empathy on a task. That means participants reported stronger feelings for others. Recognising another person's emotion is a separate ability. Effects vary with the person and situation. Acute risks include dangerous overheating, disturbances in blood sodium, raised blood pressure and severe anxiety. Other substances can add further risk.

A feeling of closeness and a laboratory empathy score each describe part of an experience. Neither predicts an individual's outcome or safety.

• NIH NIDA: MDMA, experiences and health effects
• NIH NIDA: MDMA research report, mechanisms and acute risks
• Hysek, Simmler and colleagues, 2012: transporter experiments and a controlled human study
• Hysek, Schmid and colleagues, 2014: emotional empathy and social behaviour in 32 volunteers
• Verrico, Miller and Madras, 2007: MDMA and human messenger transporters

DMT can strongly alter experience through brain signalling, while the meaning of the experience requires separate interpretation.

Ideas from Christopher Timmermann and colleagues; Anna Rickli and colleagues; Rick Strassman and colleagues; NIH NIDA · DMT brain imaging, molecular assays, human experience research and public health information

Each research team is credited in the sources. The lesson and dream analogy are original teaching material; illustrations are simplified.

In 2023, Timmermann and colleagues studied 20 healthy volunteers with DMT and placebo. EEG measured electrical activity at the scalp; fMRI tracked blood-related signals associated with brain activity. They observed greater diversity in electrical signals and changes in the relationships between brain areas. Functional connectivity means signals vary together. Those measurements and experience ratings help locate patterns worth testing further.

Laboratory studies show DMT interacts with several targets. The serotonin 5-HT2A receptor is a key part of the classic psychedelic explanation; scientists continue to investigate other contributions. A powerful feeling of discovering reality is an experience researchers can study. Establishing a claim about the outside world requires additional evidence.

Small studies use selected, monitored volunteers. DMT can cause intense fear or disorientation and raise heart rate and blood pressure. Individual effects vary.

• Timmermann and colleagues, 2023: human DMT study using EEG and fMRI
• Rickli, Moning, Hoener and Liechti, 2016: receptor and transporter laboratory assays
• Strassman, Qualls, Uhlenhuth and Kellner, 1994: reported DMT experiences
• Strassman and Qualls, 1994: measured body responses to DMT
• NIH NIDA: hallucinogen research report

Serotonin receptors translate suitable molecular contacts into cell-specific responses.

Ideas from David Goodsell and the RCSB Protein Data Bank; Dale Purves and colleagues · Serotonin Receptor; Neuroscience: Serotonin Receptors

These sources explain the molecular biology. The doorbell example and wording were created for Learn.

Read 5-HT2A as an address label. 5-HT is another name for serotonin; 2A identifies one receptor subtype. Many serotonin receptors pass their signal through helper proteins inside the cell. The 5-HT3 family instead forms a channel that lets charged particles cross the cell’s boundary. These different mechanisms help explain the variety of responses.

Psilocin can also activate 5-HT2A. Changing the activity of cells connected into a brain network can influence what a person perceives. The receiver is one part of this chain. Explaining the whole experience also requires the cell, its connections and the person’s circumstances.

A doorbell illustrates contact followed by a response. Real receptors are flexible molecules, and their effects depend on the surrounding cell and network.

• David Goodsell, RCSB PDB-101: Serotonin Receptor
• Purves and colleagues: Serotonin Receptors, Neuroscience
• NIH NIDA: Psychedelic and Dissociative Drugs

Psilocybin conversion, receptor activation and network activity form connected parts of an incomplete explanation of experience.

Ideas from Martin K. Madsen, Boris B. Quednow, Joshua S. Siegel and their research teams · Human studies of receptor engagement, receptor blockade and brain-network changes

The individual studies are linked in Sources. The pathway and wallpaper example are original teaching explanations for Learn.

Researchers test different links in this chain. A 2019 PET study of eight healthy volunteers found that estimated 5-HT2A occupancy tracked reported intensity. A controlled study of 16 volunteers found that ketanserin, which blocks 5-HT2A among other targets, reduced several psilocybin effects. Together these results support this receptor’s important contribution. Drug selectivity and measurement assumptions limit how precisely each result isolates a mechanism.

In 2024, repeated fMRI scans of seven healthy adults showed large temporary changes in the usual coordination of brain signals after psilocybin. Some regions’ signals became less synchronised, and distinctions between networks weakened. fMRI follows blood-oxygen changes related to activity. Connecting these patterns to a specific feeling remains an active research question. A small brain-imaging study provides evidence about mechanisms; clinical benefits need separate patient trials.

The overall pathway has strong support, while many details remain uncertain. Responses vary. Psilocybin can cause intense anxiety, confusion and physical effects, including nausea and raised blood pressure.

• Madsen and colleagues, 2019: human PET receptor-occupancy study
• Quednow and colleagues, 2012: controlled ketanserin blockade study
• Siegel and colleagues, 2024: Psilocybin desynchronizes the human brain
• NIH NCCIH: Psilocybin for Mental Health and Addiction
• Correction: figures 2 and 3 renumbered; contents and captions unchanged

Scientific study combines subjective reports with measurements while keeping their meanings distinct.

Ideas from NIH NIDA, NIH MedlinePlus, NIH NIBIB; Joshua S. Siegel and colleagues · Public explanations of psychedelic effects and brain measurement; human imaging research

Sources support the reported effects and measurement methods. The three-view comparison and example were created for Learn.

Reports under classic psychedelics include vivid patterns, stronger feelings and a changed boundary between oneself and the world. Enjoyment and distress can occur within the same experience. The person’s expectations, surroundings and biology influence what happens. Questionnaires turn parts of a description into scores, which makes comparison easier while leaving some of the experience unrecorded.

A scan supplies measurements that require interpretation. In the studies linked here, researchers compare changing signals with participants’ ratings. These recordings give indirect or combined views of many cells, with limited detail about a person’s moment-to-moment experience. An explanation linking receptors, networks and feelings remains a testable model. Claims about what exists outside the mind need independent evidence, even when an experience feels deeply convincing.

This overview focuses on reports under classic psychedelics such as psilocybin. Experiences differ by substance and person. Panic, confusion and other harmful effects are part of the evidence too.

• NIH NIDA: reported effects and risks of psychedelic drugs
• NIH MedlinePlus: EEG
• NIH NIBIB: MRI and functional MRI
• Siegel and colleagues, 2024: brain imaging and reported psychedelic experience

Ayahuasca combines cultural history with interacting plant chemicals; understanding its effects requires both biological evidence and context.

Ideas from Indigenous Amazonian communities; Peru Ministry of Culture; Jordi Riba, Fernanda Palhano-Fontes, José Carlos Bouso and colleagues · Living cultural traditions, official heritage records, pharmacology, clinical research and survey evidence

Community traditions retain their own meanings and histories. The teaching text and mechanism diagrams are original simplifications of the credited sources.

Peru recognised native Amazonian communities’ traditional ayahuasca knowledge and use as national cultural heritage in 2008. Traditions differ across communities. Ceremonial meaning, cultural continuity and clinical outcomes are separate subjects, each deserving its own evidence.

The 29-person depression trial provides an early clinical signal. Its small sample, short comparison and difficulty concealing a noticeable psychedelic experience limit interpretation. A 2025 experiment examined inflammatory markers and behaviour in rats; that animal model supplies a different level of evidence.

The Global Ayahuasca Survey recorded experiences from 10,836 respondents across more than 50 countries. Some reported seeking medical or psychological support. Retrospective, self-selected surveys can reveal experiences worth investigating, while their percentages cannot establish risk across all users.

MAO-A also helps process other substances. Combining MAO inhibition with some serotonergic medicines, including antidepressants, can create serious interaction risks such as serotonin toxicity. Medication changes require clinical advice; prescribed treatment should never be stopped to attend a ceremony.

Ayahuasca can cause vomiting, psychological distress and cardiovascular changes. Composition, health conditions and medicine interactions affect risk. Small clinical studies cannot establish safety for everyone or a reliable treatment outcome.

• Riba and colleagues, 2003: human pharmacology in 18 volunteers
• Palhano-Fontes and colleagues, 2019: placebo-controlled trial in 29 people with depression
• Sousa and colleagues, 2025: inflammatory and behavioural findings in rats
• Peru Ministry of Culture: 2008 recognition of traditional Amazonian ayahuasca knowledge
• Callaway and Grob, 1998: potential interactions with serotonin-reuptake inhibitors
• Bouso and colleagues, 2022: adverse experiences in the Global Ayahuasca Survey

San Pedro links Andean plant traditions with mescaline pharmacology; a receptor experiment explains one piece of that larger story.

Ideas from Andean communities and Saraguro healers; Royal Botanic Gardens, Kew; Peru Ministry of Culture; Claudia Armijos, Klaiber and colleagues · Botanical records, cultural heritage, community ethnobotany and controlled mescaline research

The teaching text and diagrams are original. Cultural sources are attributed to their communities and regions; the human trial concerns isolated mescaline.

Cactus representations associated with pre-Hispanic northern Peruvian cultures, including Chavín, contribute to the historical record. Archaeological interpretations and living practice provide distinct evidence. In 2022, Peru recognised San Pedro knowledge and use in northern Peruvian curanderismo, a tradition of healing that also incorporates later Christian influences.

A 2014 ethnobotanical study documented knowledge shared by ten Saraguro healers in southern Ecuador in collaboration with their Healers Council. These accounts belong to a particular community and setting. Andean practices have diverse local histories.

The 2024 mescaline experiment measured acute experience, cardiovascular responses and drug handling in screened healthy volunteers. It tested isolated mescaline. Clinical benefit, long-term safety and outcomes from entire cactus preparations each require their own evidence.

Mescaline can raise blood pressure and heart rate; nausea and vomiting occurred in controlled research. Altered perception, fear or confusion can add risk. A plant’s origin and cultural history cannot establish its safety for every person.

• Royal Botanic Gardens, Kew: Echinopsis pachanoi, names and native range
• Peru Ministry of Culture, 2022: San Pedro knowledge in northern Peruvian curanderismo
• Armijos, Cota and González, 2014: ethnobotany with ten Saraguro healers in Ecuador
• Klaiber and colleagues, 2024: mescaline and receptor blockade in 16 healthy adults
• Carod-Artal and Vázquez-Cabrera, 2006: archaeological and ethnographic history
• NIDA: psychedelic drugs, experiences and health risks

Shulgin's work links molecules, reported experiences and questions that controlled research can investigate.

Ideas from Alexander and Ann Shulgin · PiHKAL, TiHKAL, a published interview, historical documentation and controlled human research

Historical observations and personal views are attributed to their sources. The lesson and diagrams are original explanations.

Five compounds Shulgin singled out: PiHKAL's 2C-T-7 commentary places 2C-T-7, 2C-T-2, 2C-B, mescaline and 2C-E together near the top of his personal assessment of phenethylamines. The passage gives a group without a numbered order. These names identify a historical judgement about experiences.

Chemistry as a research tool: in his interview with Scott Moore, Shulgin described new compounds as possible tools for investigating the mind. Discovering an unfamiliar effect could open a question for research or future medicine.

Character of experience: Shulgin argued that strength captures only one feature of a compound's action. He wanted descriptions detailed enough to preserve differences between experiences, including changes in feelings and perception.

People and circumstances: his discussion of ayahuasca connected an experience with its cultural traditions, social setting and expectations. He treated these circumstances as part of understanding what happened to a particular person.

Openness to discovery: he described avoiding fixed favourites to keep his attention open to unfamiliar effects. He also worried that repeated exposure could make him less sensitive to changes he was trying to observe.

Wonder and inner life: he described spirituality through surprise at what the human mind can reveal. He recognised meditation and love as other possible sources of insight. This expresses his personal interpretation of inner experience.

Ann was a writer, artist, Jungian lay therapist and co-author. Her work explored the shadow, a name for parts of ourselves we reject or hide. Her perspective helped shape the books' accounts of psychological experience.

Arikci and colleagues' 2026 study compared 2C-B, MDMA, psilocybin and placebo in 24 healthy participants. Each participant completed different conditions, allowing comparisons within the same person. Researchers collected experience ratings, body measurements and blood samples. The study examined immediate effects; claims about treating an illness require evidence in the relevant patients.

Small, self-selected groups and expectations limit what the historical reports establish about cause, safety and treatment. Controlled studies test narrower questions, and each result has limits.

• Alexander Shulgin Research Institute: Sasha’s life and research
• Shulgin Foundation: Sasha and Ann’s contributions
• Transform Press: PiHKAL publication in 1991
• Transform Press bibliography: PiHKAL and TiHKAL publication dates
• PiHKAL #20, 2C-B: reported experiences and commentary
• PiHKAL #43, 2C-T-7: the five named compounds in the commentary
• Alexander Shulgin interviewed by Scott Moore: discovery, experience and wonder
• Shulgin Foundation: 2C-B and Shulgin’s 1974 research
• Arikci and colleagues, 2026: controlled crossover study of 2C-B, MDMA and psilocybin in 24 healthy participants
• FDA, July 2026: considerations for psychedelic clinical investigations

2C-B research connects a particular molecule with acute effects; product identity and the limits of small studies remain central to interpreting the evidence.

Ideas from Alexander Shulgin; UNODC; Nicholas Cozzi; Patrick Mallaroni, Denis Arikci and colleagues; DEA; FRANK · Chemical history, receptor experiments, controlled human research and public-health information

The teaching text and diagrams are original simplifications. Laboratory mechanisms, human outcomes and market-product warnings are described separately.

A 2026 cell study measured 2C-B binding and activation of human 5-HT2A receptors. Cells expressing a receptor help isolate one biological interaction. A living brain adds other targets, metabolism and connected networks. The study’s author disclosed a financial interest in the research institute.

A 2023 study involved 22 healthy people with previous psychedelic experience. It compared 2C-B with psilocybin and placebo and measured mood, cognition and body responses. Selected volunteers and controlled environments limit how widely these findings can be applied.

The name 2C-B identifies one compound. Products sold as tusi or pink cocaine commonly contain mixtures of other drugs. DEA testing documents unreliable market names and variable ingredients. Findings about identified 2C-B therefore cannot establish the effects or safety of an unknown powder.

Possible risks include distress, panic, confusion and impaired judgement. Physical responses, interactions and underlying health conditions also matter. Small acute studies cannot establish general safety or a therapy, and uncertain product identity adds risk.

• UNODC: phenethylamines and the 1974 synthesis of 2C-B
• Cozzi, 2026: 2C-B binding and activity at human 5-HT2A receptors in cells
• Mallaroni and colleagues, 2023: acute effects in 22 healthy volunteers
• Arikci and colleagues, 2026: controlled comparison in 24 healthy volunteers
• DEA: the variable contents of products called pink cocaine or tusi
• FRANK: 2C-family risks and uncertain product identity

5-MeO-DMT has promising clinical evidence whose meaning depends on the formulation, study design and follow-up.

Ideas from Warren and colleagues; Cubała and colleagues; Rucker and colleagues; Brush and colleagues; Shen and colleagues · Molecular, clinical and toxicology research

Studies are credited individually. The teaching sequence and diagrams are original simplifications.

A 2026 phase 2b trial studied GH001 in 81 patients with treatment-resistant depression. The blinded comparison lasted seven days; the primary outcome was measured on day eight. GH Research funded the trial. Noticeable drug effects may have weakened blinding.

A separate phase 1 trial studied BPL-003 in 44 healthy volunteers. Nausea, vomiting, headache and nasal discomfort were reported. A severe poisoning report involving harmaline highlights the danger of MAOIs, substances that interfere with the breakdown of certain chemicals. The pharmaceutical studies and interaction report concern different circumstances.

Clinical findings depend on formulation, patient selection and medical monitoring. Rare harms and long-term outcomes require further study. Mixing 5-MeO-DMT with MAOIs can be dangerous.

• Warren and colleagues, 2024: structural pharmacology of 5-methoxytryptamines
• Cubała and colleagues, 2026: GH001 placebo-controlled depression trial
• Rucker and colleagues, 2024: BPL-003 phase 1 placebo-controlled study
• Brush and colleagues, 2004: severe poisoning involving harmaline and 5-MeO-DMT
• Shen and colleagues, 2010: metabolism and drug interactions

A molecule, a mixed secretion and a cultural practice each need evidence suited to the claim being made.

Ideas from Luccioni and colleagues; Anny Ortiz Bernal and colleagues; Andrew Weil and Wade Davis; Indigenous Medicine Conservation Fund · Toad chemistry, historical research and conservation context

The desk example and diagrams are original. Historical hypotheses are labelled as hypotheses.

Luccioni and colleagues analysed secretions from 26 toads in 2025 and detected 5-MeO-DMT with other related compounds. Their method had limits for comparing concentrations. The presence of several compounds creates research questions about mixtures; added therapeutic value remains unestablished.

Modern popularisation includes Albert Most’s 1984 pamphlet. Weil and Davis proposed possible pre-Columbian use in 1994. Ortiz Bernal and colleagues’ 2026 historical analysis finds ancient continuity claims unsupported. Toad symbolism, present-day community practices and commercial narratives each require careful attribution. Growing demand also raises conservation concerns.

Secretion composition and clinical context matter. Claims of ancient continuity or added healing effects require their own evidence. Intense drug effects and dangerous interactions remain relevant.

• Luccioni and colleagues, 2025: chemical study of Sonoran Desert toads
• Ortiz Bernal and colleagues, 2026: historical analysis of toad-use claims
• Weil and Davis, 1994: report and hypothesis about historical toad use
• Indigenous Medicine Conservation Fund: discussion of cultural history and conservation
• Brush and colleagues, 2004: severe poisoning involving harmaline and 5-MeO-DMT

Sananga has documented cultural contexts, variable plant identity and unresolved clinical questions about eye benefits and safety.

Ideas from Saulo Conde Fernandes; Carmen X. Luzuriaga-Quichimbo and colleagues; Pakayaku community contributors; Revista Fitos review authors; FDA · Ethnography, botanical research, evidence review and eye safety guidance

Community knowledge is attributed to its documented context. The notebook explanation and visuals are original teaching material.

Fernandes’s 2018 ethnography records changing ritual networks and an interview with Hundu Shawan, a Jaminawá-Arara participant, who described multiple plant sources. A separate botanical study documents T. sananho, called sikta, in Pakayaku, Ecuador. Its Canelo-Kichwa informants described several uses. Those findings have specific community contexts.

A 2023 review combines cultural reports, chemistry and preclinical research. Studies of isolated substances or other plant extracts leave the clinical effects of eye preparations unresolved. Robust controlled human evidence for improved eyesight or treatment of eye disease was not identified in this research. Reported burning and questions about sterility warrant attention.

Human eye safety and efficacy remain unestablished. Eye drops must be sterile; contamination can cause serious infection. Cultural accounts and laboratory findings each have limited scope for clinical claims.

• Saulo Conde Fernandes, 2018: Sananga in ritual networks, pp. 301–302
• Luzuriaga-Quichimbo and colleagues, 2018: sikta in the Canelo-Kichwa community of Pakayaku
• Revista Fitos, 2023: integrative review of Tabernaemontana sananho
• FDA: eye-drop sterility and infection risks

Psychedelics act through molecules and cells, while their full effects depend on the person and wider context.

The term classic psychedelic groups substances partly by a shared biological action involving serotonin receptors. Ketamine, MDMA and other substances often appear in broader discussions, and their main mechanisms differ. A useful first step is to identify the particular substance and the particular effect being explained.

Keep four questions visible: What did a person report? What did researchers measure? What mechanism could connect them? What further test would distinguish explanations? This route lets a striking experience become a subject of careful investigation.

The molecule-to-experience chain is a learning map. Researchers are still working out how individual mechanisms combine into particular experiences.

• NIH NIDA: Psychedelic and Dissociative Drugs
• Neuroscience: Neural signalling

A molecule's atomic arrangement shapes its chemical contacts and possible biological effects.

The next level explains attraction through electrical charge and electron arrangements. For this lesson, the useful causal step is smaller: a change in molecular structure can change contact with a protein, which can change the protein’s behaviour.

Ball-and-stick drawings simplify moving molecules. Colour, scale and empty space in the picture are chosen to help you read the model.

• NIH NIGMS: Chemistry and pharmacology glossary
• NIH PubChem: Psilocin molecular record

Receptors turn suitable molecular contacts into changes shaped by a cell's internal machinery.

An agonist is a molecule that activates a receptor. An antagonist occupies a receptor in a way that blocks activation by another molecule. These terms describe a measured interaction. The outcome for the whole organism also depends on which cells carry that receptor and how those cells are connected.

A receptor can adopt several shapes, and several substances can interact with it. A lock-and-key picture is a useful first sketch; adding flexible shapes and different responses makes the picture closer to biology.

The doorbell analogy shows a causal sequence. Receptors are flexible proteins surrounded by moving molecules.

• RCSB Protein Data Bank: Serotonin receptor
• NIH NIGMS: Chemistry and pharmacology glossary

Serotonin's effects depend on where it is released, which receptors receive it and the surrounding activity.

Serotonin is also called 5-hydroxytryptamine, shortened to 5-HT. The letters on receptor names identify this messenger system. Further numbers and letters identify receptor families and subtypes, helping researchers distinguish different molecular receivers.

Serotonin also has roles outside the brain, especially in the digestive system. To understand a claim about serotonin, first locate the tissue and receptor being discussed. Then ask which outcome was measured and how that outcome connects to the wider claim.

A serotonin level by itself cannot describe a person’s mood. Location, receptor type, timing and interacting systems all matter.

• Biochemistry, Serotonin: NCBI Bookshelf
• Neuroscience: Serotonin receptors

5-HT2A receptor evidence helps connect psychedelic molecules with altered experience, within a larger interacting system.

A human PET imaging study estimated how much of the available 5-HT2A receptor population was occupied after psilocybin. Greater occupancy was associated with greater reported intensity. PET adds a measurement of receptor engagement to the participant’s description of experience.

Each method contributes a different answer. Structural studies describe contact; blocking experiments test dependence on a target; imaging estimates engagement. Comparing these methods strengthens an explanation, while each method retains limits such as measurement assumptions and drug selectivity.

5-HT2A is a major part of the explanation. Particular experiences and longer-term outcomes depend on additional biological and contextual factors.

• Human experiment, 2013: Blocking 5-HT2A and visual effects
• Human PET study, 2019: Psilocin and 5-HT2A occupancy
• Correction: figures 2 and 3 renumbered; contents and captions unchanged

Psilocybin's conversion into psilocin connects the starting substance with important brain-receptor effects.

A substance that is converted into an active form is called a prodrug. Understanding that conversion helps explain why the material entering the body and the molecule engaging a receptor can have different names. Researchers can measure these molecules separately.

The timeline of an effect depends on several stages: conversion, movement through the body, receptor interaction and clearance. A complete explanation follows these stages together. A picture of receptor binding captures just one moment in that longer process.

The diagram simplifies several overlapping bodily processes and provides no prediction of an individual’s experience or timing.

• NIH NCCIH: Psilocybin research and health effects
• NIH PubChem: Psilocybin molecular record
• NIH PubChem: Psilocin molecular record

A psychedelic's time course depends on its molecular interactions and how the body handles it.

Structural research visualises how several psychedelics sit within the 5-HT2A receptor and which molecular contacts they make. This helps explain why the phrase “acts at the same receptor” still leaves many detailed questions open.

A controlled comparison reduces some differences between participants by studying several conditions in the same people. The result describes that sample and experimental setting. Expectations, setting and other circumstances can influence experiences outside that comparison.

A shared drug family gives a starting classification. Specific findings depend on the molecule, outcome and conditions studied.

• Human comparison, 2022: LSD and psilocybin
• Primary research, 2025: Structures of psychedelic receptor interactions

Cell signalling passes an influence through physical interactions between receiving proteins and internal machinery.

The 5-HT2A receptor belongs to the G protein-coupled receptor family. Laboratory experiments examine how different molecules influence G-protein and other signalling pathways. Findings depend on the cellular system, timing and measurement used, so one simple chain gives only a starting model.

A cell already has its own chemical state and incoming influences. A receptor interaction joins that ongoing activity. To connect this event to a perceptual change, the next step is to examine how altered cells influence the circuits containing them.

Laboratory measures of individual signalling pathways leave open how those pathways combine to produce particular human experiences.

• Laboratory research, 2023: 5-HT2A signalling pathways
• Neuroscience: Neural signalling

Functional-connectivity diagrams show relationships between measured signals that need careful interpretation.

The default mode network includes areas involved in internally directed processes such as remembering and thinking about oneself. A 2024 repeated-imaging study found prominent psilocybin-related changes involving this network. The network continues participating in a wider changing brain.

A 2026 human study compared rest, music, meditation and a film. Its analyses found that the organisation of activity under psilocybin depended on context. This adds detail to accounts focused on desynchronisation: patterns can change in structured ways as the surrounding task changes.

Functional connectivity measures relationships between signals. The lines require additional evidence before being interpreted as direct causal communication or new anatomical connections.

• Human imaging study, 2024: Psilocybin and network synchrony
• Human imaging study, 2026: Brain activity and context

Perceived appearance depends on sensory information and the brain's changing way of processing it.

The REBUS model proposes that psychedelics can reduce the influence of some strongly held, higher-level expectations. This may allow other information to influence experience more. The proposal links several observations, and its detailed predictions remain subjects of research.

Human experiments have measured changes in visual brain responses and their relationship to reported visual effects. A useful explanation keeps the observation, the person’s report and the proposed mechanism visible as three connected pieces of evidence.

Changes in experienced appearance show that perception depends on processing. Conclusions about the ultimate nature of reality require additional philosophical arguments.

• Theoretical model, 2019: REBUS and the Anarchic Brain
• Human experiment, 2013: Blocking 5-HT2A and visual effects
• Human imaging study, 2016: Neural correlates of LSD

A changed sense of self is a reportable experience whose mechanisms and wider meaning require separate investigation.

Imaging studies of psilocybin have linked changes in self-experience with changes across connected systems. Another human study examined regional glutamate changes alongside reported ego dissolution. These findings motivate further tests of how chemistry and network activity contribute to experience.

People can describe similar changes with very different emotional meanings, including connection, relief, confusion or fear. To study them carefully, researchers distinguish aspects of the experience and examine individual reports alongside group-level results.

A powerful feeling of certainty is itself an experience to investigate. Establishing a claim about reality requires evidence and arguments beyond that feeling.

• Human imaging study, 2015: Psilocybin and ego dissolution
• Human experiment, 2020: Glutamate and altered self-experience

Animal imaging shows that some structural effects can outlast acute exposure, with human consequences still requiring evidence.

A 2021 study repeatedly imaged neurons in living mice and found increased growth of dendritic spines after psilocybin. Some newly formed spines persisted. This provides direct evidence of a structural change in that animal model.

A 2025 mouse study combined imaging with targeted interventions in particular cell types and receptors. It connected molecular targets, cellular changes and measured behaviours more closely. Human benefits, durability and harms still require human studies designed to measure those outcomes.

Cellular plasticity describes a capacity for change. Whether a particular change helps a person depends on its consequences and the evidence from that population.

• Mouse study, 2021: Growth of dendritic spines
• Mouse study, 2025: Cell types, receptors and lasting changes

Mental state and surroundings help shape a psychedelic experience alongside biological factors.

A prospective study collected information before and after planned psychedelic experiences. It found associations between psychological and contextual factors and reported responses. Because people chose their own circumstances, the study could not isolate every cause.

Clinical trials usually select participants, prepare them, provide support and follow outcomes afterwards. Those procedures form part of the studied intervention. A trial’s result must be interpreted alongside these conditions when considering how far it applies to other populations or situations.

Set and setting describe influences on variation. They cannot guarantee a particular outcome or remove the possibility of distress and other adverse effects.

• Prospective observational study, 2018: Predicting responses
• Randomised clinical trial, 2022: Cognitive and emotional functions
• NIH NCCIH: Psilocybin research and health effects

Clinical claims need comparison-based evidence for particular people, outcomes and harms.

A 2022 randomised trial in treatment-resistant depression found improvement on its main short-term comparison under a specified psilocybin intervention with psychological support. It also recorded adverse effects, and some longer-term results were less conclusive. The outcome is strongest when described with its population, comparison and time point.

Blinding means trying to keep participants and assessors unaware of the assigned condition. Psychedelic effects can make that difficult, allowing expectations to affect outcomes. Replication, clear reporting, credible comparisons and follow-up help researchers judge how robust and generalisable a result is.

Therapeutic findings concern particular conditions, people and interventions. Individual benefit, longer-term effects and uncommon harms require further evidence.

• Randomised clinical trial, 2022: Treatment-resistant depression
• NIH NCCIH: Psilocybin research and health effects