Richard Zeifman

Richard Zeifman

How Does Psilocybin Therapy Work?: Exploring Experiential Avoidance as a Mechanism of Change



Psilocybin therapy shows promise as an intervention for improving a wide range of mental health outcomes (e.g., well-being; Johnson et al., 2018). However, there remains an incomplete understanding of the underlying psychological mechanisms that explain its therapeutic action. Qualitative research suggests that experiential avoidance may play a key role in psilocybin therapy (Watts et al., 2017), suggesting that further research into experiential avoidance as a mechanism underlying psilocybin therapy is warranted. Methods:We conducted a within-subject experimental study in which healthy, psychedelic-naïve, individuals (N=17) were administered a low and high dose of psilocybin. At baseline, as well as 4-weeks after low and high-dose psilocybin, individuals completed self-report measures of experiential avoidance and well-being. Results:A repeated measure ANOVA with post-hoc tests indicated that high dose psilocybin (p=.002; Cohen’s d=3.59), but not low-dose psilocybin (p=.08; d=1.88), led to significant increases in well-being. Similarly, high dose psilocybin (p=.004; d=3.36), but not low-dose psilocybin (p=.269, d=1.15), led to decreases in experiential avoidance. Furthermore, changes in experiential avoidance were significantly associated with changes in well-being following high-dose psilocybin (r=.51, p=.035), but not low-dose psilocybin (r=-.08, p=.769).


Our findings indicate that a single high-dose of psilocybin leads to decreases in experiential avoidance and increases in well-being among healthy individuals. These results suggest that experiential avoidance may be a transdiagnostic mechanism underlying outcomes associated with psilocybin therapy. Furthermore, integrating psilocybin and psychotherapeutic interventions that specifically target experiential avoidance (e.g., acceptance and commitment therapy [ACT]; Hayes, Strosahl, & Wilson, 2012) may optimize treatment outcomes.


Richard Zeifman is a PhD student in Clinical Psychology at Ryerson University and a research intern at the Centre for Psychedelic Research at Imperial College London. Richard’s research focuses on evidence-based interventions for highly suicidal individuals, as well as mechanisms of change underlying psychotherapeutic outcomes. He is particularly interested in exploring psychedelics as novel interventions for suicidality, as well as identifying psychological mechanisms that account for the therapeutic effects associated with psychedelic therapy.



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