Psilocybin and Personality Change: The Openness Research
Personality is among the most stable of psychological constructs. Longitudinal studies show that the Big Five personality traits — openness, conscientiousness, extraversion, agreeableness, neuroticism — typically change only slowly across decades of life. Yet a 2011 study from Johns Hopkins demonstrated something remarkable: a single high-dose psilocybin session could produce lasting increases in one of these traits, particularly openness to experience.
The MacLean Study
Katherine MacLean, then a postdoctoral researcher in Roland Griffiths' lab at Hopkins, led the study published in the Journal of Psychopharmacology in 2011.
Design: 51 healthy adults with no prior psychedelic experience completed personality assessments (NEO-PI-R) before and after psilocybin sessions. Sessions were double-blind, with participants receiving either psilocybin or methylphenidate (active control) in two sessions.
Finding: Openness to experience increased significantly after psilocybin, particularly in participants who had a complete mystical experience during the session. The increase was not subtle — roughly equivalent to the average amount of openness change that occurs over an entire adult lifespan under normal conditions.
Duration: Follow-up assessments at 1 year confirmed the openness increase was maintained. This is not a transient post-session afterglow — it is a lasting change in a stable personality trait.
What Is Openness to Experience?
Openness is one of the Big Five personality traits, characterized by:
- Aesthetic sensitivity and appreciation
- Active imagination and fantasy
- Intellectual curiosity
- Openness to new experiences and ideas
- Emotional depth and expressiveness
- Willingness to examine and reconsider one's own values and beliefs
High openness is associated with creativity, intrinsic motivation, curiosity-driven behavior, and tolerance for ambiguity. It is also associated with greater psychological flexibility — the ability to hold multiple perspectives and update beliefs in response to evidence.
Low openness is associated with preference for routine, conventional thinking, resistance to change, and tendency toward more rigid mental patterns.
The Mystical Experience Connection
The most critical finding in the MacLean study was the specificity of the effect: not all participants showed increased openness. The increase was concentrated in participants who had a "complete mystical experience" during the session — scoring highly on the Mystical Experience Questionnaire (MEQ30) measures of unity, sacredness, noetic quality, and transcendence of time and space.
This is consistent with findings across multiple psilocybin trials: the mystical experience itself — not merely the pharmacological effects of the drug — is the active therapeutic ingredient. The implication for openness research: psilocybin doesn't just pharmacologically increase openness; it does so by enabling a specific type of experience that transforms how the person relates to themselves and the world.
Replications and Related Findings
The MacLean finding has influenced subsequent research significantly. Multiple studies have found:
Positive personality changes post-treatment: Reduced neuroticism, increased agreeableness, and increased conscientiousness in addition to openness — though openness remains the most consistent finding.
Psychological flexibility: Multiple studies have found increased psychological flexibility (acceptance of difficult internal states, reduced experiential avoidance) following psilocybin treatment. This is closely related to openness and is a key mechanism in multiple therapeutic applications.
Attitude and perspective changes: Studies have documented lasting changes in worldview — reduced materialism, increased nature connectedness, greater sense of meaning and purpose — following psilocybin sessions. These correlate with the openness dimension.
Clinical Implications
Increased openness has therapeutic implications across multiple conditions:
Depression: Depression is characterized partly by cognitive rigidity and closed thinking patterns. Increased openness may directly counter this.
Addiction: Recovery from addiction requires openness to identity change — willingness to see oneself differently. Increased openness supports this.
PTSD: Trauma maintains PTSD partly through closed, avoidant processing. Openness to processing traumatic material is part of what makes trauma therapy work.
General wellbeing: Openness is positively associated with wellbeing, life satisfaction, and adaptability across the lifespan.
What This Doesn't Mean
Increased openness doesn't mean increased credulity or reduced skepticism. Openness in the psychological sense is about willingness to engage with new ideas, aesthetic experience, and emotional depth — not about abandoning critical thinking. The most open individuals in personality research are often also the most intellectually rigorous, because they are genuinely curious rather than defensive.