Psychedelics for Treating Mental Disorders: A Research Overview
Summary
Dr. Matthew Johnson, Director of the Center for Psychedelic and Consciousness Research at Johns Hopkins, explores the pharmacology, clinical applications, and therapeutic mechanisms of psychedelic compounds including psilocybin, MDMA, ketamine, DMT, and LSD. The conversation covers how these substances alter self-representation and neural models, and what a structured clinical psychedelic therapy session actually looks like from screening through integration.
Key Takeaways
- Psychedelics work primarily by challenging the brain’s predictive models — dissolving rigid mental frameworks, particularly around self-identity, which may explain their therapeutic effects across vastly different conditions.
- The serotonin 2A receptor is the primary target of classic psychedelics (psilocybin, LSD, DMT, mescaline), though the mechanism of their profound effects beyond simple receptor binding remains poorly understood.
- Changes in self-representation appear to be the common therapeutic denominator — whether treating depression, cancer-related anxiety, or addiction — more so than the specific content of the psychedelic experience.
- HPPD (hallucinogen-persisting perceptual disorder) is real but extremely rare, and has never been observed in thousands of clinical trial participants — only in illicit use contexts, suggesting factors like dose uncertainty, polypharmacology, or rare neurological susceptibility.
- Integration after the session — writing about the experience, discussing it with guides, and taking it seriously — may be as therapeutically important as the session itself.
- Flashbacks are likely not drug-related in the traditional sense; most are either state-dependent memory retrieval or brief perceptual anomalies in the day or two following use. Fat storage of psychedelics has no scientific evidence.
- Ketamine (as Spravato/esketamine) is FDA-approved for treatment-resistant depression, but its antidepressant effects last roughly one week vs. one year or more for psilocybin — a gap that may relate to whether ketamine is administered using a full psychedelic therapy model.
- Set and setting — the therapeutic relationship, preparatory sessions, and physical environment — critically shape the psychedelic experience and its outcomes.
- Big life decisions (ending relationships, quitting jobs) should be deferred at least one to two weeks following a psychedelic session.
Detailed Notes
What Is a Psychedelic?
The term “psychedelic” is more cultural than pharmacological, spanning multiple distinct drug classes. Dr. Johnson defines psychedelics broadly as substances with the ability to profoundly alter one’s sense of reality, including the sense of self.
Major classes:
- Classic psychedelics (serotonin 2A agonists): psilocybin, LSD, DMT, mescaline
- Structurally divided into tryptamines (psilocybin, DMT) and phenethylamines (mescaline)
- NMDA antagonists: ketamine, PCP, dextromethorphan
- Kappa-opioid agonists: Salvinorin A (from Salvia divinorum)
- Entactogens/Empathogens: MDMA — works via serotonin release (flooding the synapse), not receptor agonism like classic psychedelics
“All of the classic psychedelics serve as agonist or partial agonists at the serotonin 2A receptor.”
How Classic Psychedelics Work
- Psilocybin is structurally similar to serotonin (both tryptamine-based), but activates the 5-HT2A receptor differently — triggering alternate downstream signaling
- Classic psychedelics also increase glutamate transmission, which may explain overlap with ketamine’s psychedelic effects
- The brain is described as a prediction machine, operating top-down; psychedelics appear to dissolve or destabilize these predictive models
- Neuroplasticity is triggered by the experience; the actual neural rewiring is a process, not a single event, and may unfold over months or years
The Clinical Psilocybin Session: Step by Step
Screening:
- Structured psychiatric interviews (using DSM criteria)
- Exclusion criteria include: psychotic disorders (schizophrenia), bipolar disorder (particularly manic features), significant cardiovascular disease
Preparation (several hours across multiple sessions):
- Participants develop therapeutic rapport with their guides/therapists
- Informed of the wide variability of possible experiences — described as “all arounders”: potentially the most beautiful or most terrifying experience of one’s life
Dosing:
- Pure synthetic psilocybin administered in a small capsule (white powder)
- Typical therapeutic dose range: 20–30 mg (historically body-weight adjusted to ~70 kg; newer protocols dropping this adjustment)
- Onset: 15–60 minutes; average ~30 minutes
- Duration: approximately 6–8 hours
During the session:
- Participants lie on a couch wearing eyeshades (not “blindfolds”) to encourage internal focus
- Music is played
- Blood pressure and pulse monitored every ~30 minutes
- Protocol exists for cardiovascular intervention if needed (nitroglycerin sublingually); rarely required
- Emotional expression — including crying — is explicitly welcomed and encouraged
- Guides are present throughout; no cognitive tasks or fMRI during therapeutic sessions
Integration:
- Brief initial discussion ~5–6 hours into the session (late afternoon)
- Overnight homework: write about the experience (no length requirement, no judgment)
- Next-day 1–2 hour integration session with guides to discuss the experience and its meaning
- Supportive, non-directive therapy style; humanistic approach with unconditional positive regard
- Participants encouraged not to make major life decisions for at least 1–2 weeks
Therapeutic Mechanisms: Self-Representation
The leading hypothesis for why psychedelics work across such diverse conditions:
“The common denominator are persisting changes in self-representation — the fundamental relationship of a person in the world.”
- The self is the brain’s largest predictive model: “I am a smoker,” “I am a depressed person,” “I am a failure”
- Psychedelics appear to dissolve or loosen this model, allowing it to be rebuilt differently
- This is not driven by language or affirmations — neural networks change in response to experience, not words
- Falling in love with a pen, or processing childhood trauma, may both lead to the same endpoint: a transformed relationship with self and world
- Memory reconsolidation may play a role, particularly in trauma processing — memories appear to be reprocessed during the experience in lasting ways
Examples from clinical work:
- Smoking cessation: participants report suddenly recognizing they can simply decide not to smoke — identity shift from “I am a smoker who can’t quit” to a non-smoker
- Cancer patients: reduction in existential fear; recognition that suffering was partly self-generated; renewed engagement with life
- These are described as “duh” experiences — insights that seem obvious but were previously inaccessible
Ketamine and NMDA Antagonists
- Ketamine (as Spravato/esketamine) is FDA-approved for treatment-resistant depression
- Current clinical model does not frame the psychedelic experience as therapeutically relevant — it is treated as a “side effect”
- Antidepressant effects last approximately one week, versus one year or more for psilocybin
- Russian research by Krupitsky in the 1990s–2000s used high-dose ketamine as psychedelic therapy for heroin and alcohol addiction, with high success rates
- The gap in durability between ketamine and psilocybin may reflect the absence of a psychedelic therapy framework for ketamine
- A “K-hole” refers to a heavily dissociative state at higher doses (~75–100 mg+)
Flashbacks and HPPD
Hallucinogen-Persisting Perceptual Disorder (HPPD):
- Real diagnosis in the DSM: persisting visual disturbances (halos, trails, color distortions) lasting months, causing clinical distress
- Never observed in thousands of clinical trial participants across the modern and historical research eras
- Only documented in illicit use — likely due to unknown doses, purity issues, polypharmacology,