Psychedelic-Assisted Psychotherapy
A classic psychedelic is administered a small number of times inside an intensive course of preparation, monitored dosing and integration, on the hypothesis that a period of increased psychological flexibility and relaxed prior beliefs allows entrenched patterns to be revised in ways that ordinary therapy cannot easily reach.
The drug does not do the therapy. It opens a window, and what happens in that window is the treatment.
Who built it
Humphry Osmond & Abram Hoffer
Psychiatrists, Saskatchewan
Ran the first substantial LSD programme for alcohol dependence in the 1950s. Osmond coined the term "psychedelic". Their results were encouraging and their methods, by contemporary standards, uncontrolled.
First waveStanislav Grof
Psychiatrist
The most systematic clinician of the first wave; developed the framework of set, setting and non-directive support that contemporary protocols still use, and documented thousands of sessions before the research was halted.
First wave / transpersonalRoland Griffiths
1946–2023Psychopharmacologist, Johns Hopkins
The 2006 psilocybin study that restarted the field with credible methodology, and the subsequent programme on psilocybin for depression, addiction and distress in life-threatening illness.
Second waveRobin Carhart-Harris
Neuroscientist, Imperial College London and UCSF
The entropic brain hypothesis and the REBUS model (relaxed beliefs under psychedelics), the leading contemporary mechanistic account, and the first modern trials of psilocybin for treatment-resistant depression.
Second wave
Theory of personality
Contemporary psychedelic research has adopted a broadly predictive-processing account of mind. The brain is understood as a hierarchical prediction machine: high-level beliefs constrain how sensory and interoceptive data are interpreted, and over time those beliefs become heavily weighted and self-confirming. Depression, addiction and rigid character are described as states of excessively precise, over-weighted priors — "I am worthless", "I cannot stop", "the world is hostile" — that data can no longer correct.
REBUS
Carhart-Harris and Friston’s model proposes that classic psychedelics, acting as 5-HT2A receptor agonists on deep-layer cortical pyramidal neurons, temporarily reduce the precision of high-level priors. Bottom-up information gains influence, entrenched beliefs become revisable, and the system enters a period of heightened plasticity. On this account the drug does not install anything; it loosens what is already installed, and what happens next depends on the context.
Set and setting
The oldest and most robust principle in the field, and the one most consistently confirmed. Outcome depends heavily on the person’s state and expectations (set) and on the physical, interpersonal and cultural context (setting). The same compound at the same dose produces a therapeutic experience in one context and a frightening one in another, which is precisely why this cannot be treated as a drug that works on its own.
Theory of psychopathology
The framework is transdiagnostic and explicitly about rigidity rather than about symptoms: depression as ruminative self-focus locked in place, addiction as a narrowed behavioural repertoire with a dominant reinforcer, end-of-life distress as an inability to hold mortality without terror, and obsessive presentations as pathological certainty.
- Excessive weighting of negative self-referential priors, maintained by attention and memory bias
- Increased activity and connectivity within the default mode network, associated with rumination and self-focus
- Narrowed behavioural and cognitive repertoires — the "canalised" state
- Experiential avoidance of the material that would revise the prior
Theory of change
The protocol is a three-phase structure in which the dosing session is the smallest part.
| Phase | Content | Typical duration |
|---|---|---|
| Preparation | Alliance building, history, psychoeducation, expectation setting, agreement on the "flight instructions", rehearsal of how to respond to difficulty, physical touch consent, safety planning | 2–4 sessions before each dosing |
| Dosing | Supervised administration, usually with two therapists present, eyeshades, curated music, minimal verbal interaction, non-directive support | 6–8 hours, one to three times |
| Integration | Making meaning of the experience and converting it into changed behaviour. The phase most likely to be under-resourced and the one most likely to carry the effect | 3–6+ sessions after each dosing |
Proposed mechanisms, and their evidential status
- 1Mystical-type or peak experience — measured by validated scales, and correlated with outcome in several studies. Correlation, not causation: people who respond may be more likely to report peak experience.
- 2Emotional breakthrough and processing of avoided material — supported by qualitative and some quantitative work.
- 3Increased psychological flexibility — measured and associated with outcome; the clearest link to existing therapy models.
- 4Neuroplasticity — animal and some human evidence for increased dendritic spine growth and synaptogenesis, potentially independent of subjective experience.
- 5Disruption of default mode network connectivity, with subsequent reintegration.
Key concepts
The vocabulary you need to read the literature and to be understood in supervision.
Where it sits in the transtheoretical grid
Which change processes the system leans on, and at what level of content it aims.
- Consciousness raising
Increasing information about oneself and the problem - feedback, interpretation, education, observation.
- Catharsis / dramatic relief
Experiencing and expressing affect about the problem, whether by corrective emotional experience or by evoking what has been avoided.
- Self-reevaluation
Appraising how one thinks and feels about oneself with respect to the problem; values clarification.
- Self-liberation (choosing)
Choosing and committing to act, plus the belief that one can change - the deliberate exercise of agency.
- Helping relationship
Being open and trusting about problems with someone who cares; the relationship as vehicle, and as medicine in its own right.
- Intrapersonal conflicts
- Maladaptive cognitions
- Symptom & situational problems