Psychedelics and Personality Change: What the Science Actually Shows

For most of the twentieth century, personality psychology operated under a fairly tidy assumption: the Big Five traits — Openness, Conscientiousness, Extraversion, Agreeableness, and Neuroticism — drift slowly across adulthood, but they are largely stable after age thirty. William James called personality "set in plaster" by the third decade. Decades of longitudinal data mostly agreed.

Then a small Johns Hopkins study published in 2011 reported something genuinely uncomfortable for that picture. A single high-dose session of psilocybin, the active compound in psychedelic mushrooms, appeared to produce a measurable shift in adult personality that was still detectable a year later. The trait that moved was Openness, and the magnitude of change was larger than what is typically observed in healthy adults over multiple decades of life.

Fifteen years and several phase-2 and phase-3 trials later, the picture has filled in considerably. Psychedelic-assisted therapy is no longer a fringe topic — it is being studied at most major research universities, MDMA-assisted psychotherapy has cleared phase 3 trials for PTSD, and personality change is one of the most replicated outcomes across compounds. This article walks through what the evidence actually shows, where it gets oversold, and why a particular therapy framework — Internal Family Systems — has become the de facto integration model in this space.

Curious where you sit on the Big Five right now? Take our free comprehensive personality assessment for a baseline reading on Openness, Neuroticism and the other three traits psychedelic studies most often move.

The Personality Backdrop: Why "Set in Plaster" Mattered

To appreciate why the early psilocybin findings raised eyebrows, it helps to understand the prior consensus. Big Five traits do change across the lifespan — Conscientiousness and Agreeableness tend to rise, Neuroticism tends to fall — but the year-over-year movement is small. Researchers using the NEO-PI-R, the gold-standard Big Five inventory, generally consider effect sizes of 0.10 to 0.20 standard deviations to be meaningful over five to ten years.

Therapy and major life events can move traits a bit faster, but not by much. A meta-analysis of psychotherapy trials published in 2017 estimated that several months of treatment produced average personality changes of about 0.30 standard deviations, mostly in Neuroticism. Against that benchmark, the changes reported after a single psychedelic session — sometimes 0.5 standard deviations or more in Openness — are unusual.

What the Big Five Actually Measures

Before getting into the studies, a quick refresher on the traits being moved:

• Openness — imagination, aesthetic sensitivity, intellectual curiosity, emotional depth, willingness to entertain unconventional ideas. The trait most tied to creativity and to interest in art, abstraction and meaning.
• Conscientiousness — organization, self-discipline, follow-through, goal orientation, impulse control.
• Extraversion — sociability, positive emotionality, assertiveness, energy in social settings.
• Agreeableness — warmth, cooperativeness, trust, compassion, low antagonism.
• Neuroticism — emotional reactivity, tendency toward anxiety, sadness and self-criticism. Sometimes called negative emotionality in newer instruments.

Psychedelic research most reliably moves Openness up and Neuroticism down. Other traits move too, but less consistently and usually only in clinical samples.

The Openness Effect: The MacLean 2011 Study

The foundational paper here is MacLean, Johnson and Griffiths (2011), published in the Journal of Psychopharmacology. The team gave 51 healthy adults one or more sessions of high-dose psilocybin in a controlled clinical setting, with extensive screening and a trained monitor present throughout each eight-hour session. Personality was measured with the NEO-PI-R at baseline and again more than a year later.

Across the full sample, Openness rose significantly — and more importantly, the change persisted at follow-up. But the effect was not uniform. The lasting Openness shift was concentrated in the roughly 60% of participants who reported a "mystical-type experience" during their session, characterized by a sense of unity with all things, ineffability, transcendence of time and space, and a feeling of sacredness. Participants who took the same dose without that subjective experience showed minimal personality change.

"Normally, if anything, openness tends to decrease as people get older." — Roland Griffiths, in commentary on the original Hopkins findings

That qualifier matters. The effect is not pharmacological in any simple sense. The drug is necessary but not sufficient. What seems to durably reshape Openness is the meaning-saturated subjective experience the drug enables under the right conditions.

Beyond Openness: What Newer Trials Have Found

The MacLean study used healthy volunteers. The more interesting question for the last decade has been whether personality change generalizes to clinical populations and to other traits. The answer, broadly, is yes.

Psilocybin vs. Escitalopram for Depression

A 2023 paper by Weiss, Carhart-Harris and colleagues at Imperial College London reported personality outcomes from a phase 2, double-blind, randomized trial comparing psilocybin therapy to escitalopram (a standard SSRI) for moderate-to-severe major depressive disorder. The psilocybin arm received two sessions across the trial; the escitalopram arm took daily medication for six weeks.

At week six, psilocybin therapy was associated with statistically meaningful decreases in Neuroticism, introversion, disagreeableness and impulsivity, and increases in absorption, Conscientiousness and Openness. At six months, lower Neuroticism and lower disagreeableness were still present. Escitalopram produced changes in a similar direction but smaller in several dimensions, and the between-group differences did not reach statistical significance — a useful reminder that effective antidepressant treatment of any kind nudges personality.

MDMA-Assisted Therapy for PTSD

Wagner and colleagues (2017) examined personality change in participants from earlier MDMA-assisted psychotherapy trials for chronic PTSD. They found persistent increases in Openness and decreases in Neuroticism following treatment. Critically, the magnitude of the Openness increase correlated with the magnitude of PTSD symptom reduction, suggesting Openness is not just a side effect — it may be part of how the treatment works.

This pattern — personality shift mediating clinical improvement — has shown up enough times across compounds and conditions that some researchers now treat trait change as a candidate mechanism of action, not a downstream curiosity.

Ayahuasca

Ayahuasca, the DMT-containing brew used ceremonially in parts of South America, has been studied less rigorously than psilocybin or MDMA but more naturalistically. Longitudinal studies of ceremonial users have reported increases in Agreeableness and Openness and decreases in negative emotionality, with effects sustained at six months and, in some cohorts, at a year. A recent naturalistic study added a novel finding — increases in Extraversion — that has not appeared as cleanly in psilocybin work.

The ayahuasca evidence is messier than the clinical-trial evidence because participants self-select into ceremonies and there are no placebo controls, but the direction of effect rhymes with the controlled studies on other compounds.

The IFS Intersection: Why Parts Work Pairs So Well

One of the most interesting developments in psychedelic-assisted therapy in the last several years is not a new compound — it is a particular psychological framework that has become the integration model of choice for many practitioners. That framework is Internal Family Systems (IFS), developed by Richard Schwartz in the late 1980s.

IFS treats the mind as a constellation of distinct sub-personalities or "parts." Some parts (managers and firefighters in IFS terminology) work to keep the system functioning and protected. Other parts (exiles) carry pain, shame and fear from past trauma and are kept walled off from awareness because contact with them feels intolerable. Underneath the parts is what IFS calls Self — a baseline state of calm, curiosity, compassion and clarity that every person has access to in principle. The work of IFS therapy is to unblend from protective parts, develop relationship with exiles, and let exiles unburden the painful loads they have been carrying. For a fuller introduction to the model, see our guide to discovering your IFS parts.

Why the Two Fit

Three convergences make IFS a natural fit for psychedelic work:

1. Psychedelics soften protectors. Protective parts maintain the structure of everyday selfhood by keeping painful material out of awareness. Psychedelics — psilocybin, MDMA, ayahuasca, ketamine — appear to do something similar at the neural level: they reduce the dominance of the brain's default mode network, the system most associated with self-referential rumination and rigid identity. Clinically, this manifests as protectors relaxing. Material that protectors normally guard becomes accessible.

2. The "expanded state" looks a lot like Self. The psychological qualities people most often report from a constructive psychedelic session — openness, connection, calm presence, compassion, curiosity — map remarkably closely onto the IFS description of Self-energy. This is part of why IFS therapists who began working with psychedelics describe the experience as familiar rather than novel. The Self is not absent in everyday life; it is usually crowded out by parts. Psychedelics, used carefully, can reduce the crowding.

3. Exiles can be witnessed and unburdened. The most challenging step in IFS work is sitting with exiles — the parts that hold the original wounds. In ordinary therapy this can take months of careful preparation, because protectors have to be persuaded to step back. In a psychedelic session, with protectors already softened and Self-energy more available, exiles often surface spontaneously. The integration window — the days and weeks after the session — is where IFS provides language and method for actually completing the unburdening rather than just having a striking experience.

"Psychedelics give you access. IFS gives you a map for what to do with it." — paraphrased from clinical lectures by Robert Falconer, longtime IFS trainer and co-author with Richard Schwartz of Many Minds, One Self

Schwartz himself, Michael Mithoefer (lead investigator on the MDMA-PTSD trials) and Falconer have all spoken publicly about IFS as a framework for the preparation, experience and integration phases of psychedelic-assisted therapy. None of them claim IFS is the only framework that works — but the convergence of clinicians from very different starting points on the same model is hard to ignore.

What This Means for Personality Change

The personality-change finding and the IFS framing are not separate observations. If protective parts are softened, and exiles are successfully unburdened, what changes downstream is precisely the trait profile a person presents to the world. A protector that has spent decades enforcing emotional vigilance shows up on a Big Five inventory as elevated Neuroticism. An exile carrying shame shows up as low Agreeableness or low Self-Compassion. Unburdening these parts does not just feel different; it reads differently on a personality test.

This is one plausible reading of why psychedelic-induced personality changes look the way they do — Openness up, Neuroticism down, often Agreeableness up. These are the trait correlates of a system in which exiles have been heard and protectors have been allowed to relax their roles.

The Caveats Researchers Insist On

The clinical-trial picture is more guarded than enthusiast media often suggests. Several caveats are worth taking seriously.

Set, Setting and Integration Are Part of the Intervention

Every personality finding cited above came from studies in which participants underwent multiple preparatory sessions, took the substance in a quiet room with trained support, listened to a curated playlist, and engaged in structured integration sessions afterward. Stripping out any of those elements is not the intervention that has been studied. The phrase "set and setting" has a long history in the literature for a reason: outcomes track these variables far more than they track milligram dose.

Screening Excludes a Significant Population

Trial protocols typically exclude people with personal or family histories of psychotic disorders, certain cardiovascular conditions, current bipolar I or II diagnoses, and several other categories. This is not bureaucratic caution — psychedelics can precipitate or worsen these conditions. The favorable trial outcomes are for a screened population, not the general public.

Drug Interactions Are Real

SSRIs, MAOIs and several other medication classes interact with psychedelic compounds in ways that range from blunting the experience to producing serotonin syndrome. This is one of the largest safety considerations and one of the most consistently underappreciated outside clinical settings.

Personality Change Is Not Always Improvement

Higher Openness can mean useful flexibility — or weakened critical thinking and susceptibility to fringe ideas. Lower Neuroticism can mean genuine equanimity — or a defended numbness that masks unprocessed material. The Big Five describes traits, not virtues. Practitioners who work in this space describe a small but real subset of clients who emerge from psychedelic experiences in worse psychological shape than they entered, particularly without proper integration support.

Legal and Regulatory Status Varies

Psilocybin remains a Schedule I substance under U.S. federal law. Oregon and Colorado have established regulated therapeutic frameworks. MDMA-assisted therapy was rejected for FDA approval in August 2024 despite positive phase 3 results, and the regulatory path remains unsettled. Outside structured trials and the few legal frameworks, use is illegal in most jurisdictions, and underground access carries the additional risks of unknown compounds, unknown dosing and unscreened facilitators.

You do not need a psychedelic experience to start mapping your inner system. Our free IFS-based parts assessment identifies the protectors and exiles most active in your psychology — the same map IFS therapists use during preparation and integration work.

What This Means If You Are Not Going Anywhere Near Psychedelics

The most useful takeaway from the psychedelic-personality literature, for most readers, has nothing to do with taking a substance. It is the empirical demolition of the "set in plaster" assumption. Adult personality is more changeable than the dominant model of the late twentieth century suggested. Psychedelics produce one of the larger documented effect sizes, but they are not the only mechanism of change.

Several lines of conventional research show similar (smaller) effects from:

• Sustained psychotherapy, particularly approaches that work with parts or schemas
• Sustained meditation practice, especially intensive retreat formats
• Major life role changes — entering a stable partnership, becoming a parent, taking on substantial professional responsibility
• Therapy specifically targeting Neuroticism, which is the most reliably modifiable trait

The common thread across all of these — including psychedelic work — is that durable trait change seems to require some combination of meaningful experience, time spent processing it, and a framework for integrating insight back into ordinary life. The substance is a catalyst, not the mechanism.

The Bottom Line

The evidence that psychedelics can change adult personality, particularly Openness and Neuroticism, is now robust enough to take seriously. The effect sizes are larger than what most other interventions produce, the changes persist for at least months and in some studies more than a year, and they appear across compounds, populations and research groups. This is no longer a fringe finding.

What remains unsettled is who benefits, who is harmed, and how to deliver the intervention safely outside tightly controlled trial conditions. The personality changes themselves are not the goal — they are the trace left by something deeper: protective parts loosening their grip, exiled parts being heard, and a more flexible, less defended way of inhabiting one's own experience taking root.

Internal Family Systems has emerged as the leading framework for making sense of that deeper process, both inside and outside psychedelic contexts. If the headline studies make you curious about your own inner system, the IFS-style work — mapping parts, attending to protectors, eventually witnessing exiles — is available without a substance and without a clinical trial. The science of personality change is showing that adults are more workable than we thought. The question is what each person decides to do with that.