The intensity of the psychedelic experience is reliably associated with clinical improvements: A systematic review and meta-analysis.

Background: Psychedelic-assisted therapies have demonstrated promising results in treating mental disorders, with results suggesting that the subjective intensity and quality of psychedelic experiences plays a significant role in mediating therapeutic effects. However, the strength of this association across diagnoses and treatment settings remains underexplored.

Methods: We searched MEDLINE, Embase, and PsycINFO databases for studies examining the correlation between the intensity of the psychedelic experience and clinical outcomes in patients treated with classical psychedelics. Meta-correlations were performed, and standardized mean differences of psychedelic experience intensity scores were compared between clinical responders and non-responders using random-effects models. Subgroup analyses were conducted based on diagnosis, study design, setting (clinical vs. naturalistic), and substance used.

Results: A significant positive correlation was found between the intensity of mystical experiences and clinical improvement across all studies (r = .33, p < .0001). Subgroup analyses revealed a stronger association (p = .02) for mood disorders (r = .41) compared to addictions (r = .19). The effect was greater (p < .01) in protocol-based clinical settings (r = .50) than in naturalistic use (r = .14). Prospective designs showed stronger (p < .01) correlations (r = .43) compared to retrospective designs (r = .14).

Conclusion: The intensity of psychedelic experiences is significantly and reliably associated with therapeutic outcomes, particularly in mood disorders. Clinical settings and prospective study designs strengthen this relationship, emphasizing the importance of controlled environments and therapeutic support to fully benefit from the therapeutic potential of psychedelics.