The use of the psychological flexibility model to support psychedelic assisted therapy

Watts and colleagues base their account on three elements: published quantitative outcomes from Psilodep 1, thematic qualitative analysis of interviews with Psilodep 1 participants, and the design of an ongoing clinical trial (Psilodep 2) in which the ACE model is being operationalised. Psilodep 1 was an open trial of 20 people with treatment-resistant depression who received two preparation sessions, two therapist-supported psilocybin sessions, and three integration sessions; the authors report large effect sizes for depressive symptoms at early follow-up. At six months post-treatment, the 20 participants were interviewed to identify patient-reported change processes; the investigators applied thematic analysis to these interviews to extract common experiential themes. Psilodep 2 is described as a registered randomised, double-blind trial in which participants undergo two psilocybin sessions spaced three weeks apart, with a standardised but flexible psychotherapeutic package: four preparation contacts (including one extended face-to-face Preparation 3 session), the two dosing days, and four to seven integration sessions plus optional remote sessions. The dosing sessions are non-directive—patients wear eyeshades, listen to music, and are encouraged to ‘‘go inside’’—and therapists are instructed to be supportive and minimally directive, emphasising acceptance, connection, and embodiment. Development and operationalisation of ACE involved mapping the six PFM ‘‘hexaflex’’ processes (contact with the present moment, acceptance, cognitive defusion, self as context, values, committed action) onto an acceptance triad and a connection triad, and embedding embodiment throughout. Two experiential exercises were created: P-ACE (a preparation exercise, delivered in the main preparation session) and I-ACE (an integration exercise), both of which use guided imagery and body-focused work to cultivate willingness, present-moment contact, and values-driven action. The paper describes the content and delivery of these exercises and how they are incorporated into preparation and the three-stage integration structure (narrative pulling together, distilling insights, and supporting behavioural change).

From Psilodep 1, the authors report large quantitative effects on depression: Cohen's d = 2.2 and d = 2.3 at weeks 1 and 5 post treatment, with sustained but reduced effect sizes of d = 1.5 and d = 1.4 at 3 and 6 months, respectively. These published outcome data provide the clinical context for the qualitative work. The qualitative analysis of six-month follow-up interviews identified two overarching, complementary themes: a movement from disconnection (from self, others, world) to connection, and a movement from emotional avoidance to acceptance. Participants described intense, often transformational acute experiences during psilocybin sessions and sustained changes afterwards. The researchers mapped participant accounts onto the six PFM processes and presented illustrative examples for each process. Examples included: willingness (psilocybin interrupting ruminative mental loops and enabling surrender to intense emotion); cognitive defusion (reports of ‘‘mental freedom and clarity’’ and seeing thoughts as thoughts); present-moment focus and embodiment (heightened sensory awareness, feeling ‘‘grounded’’ and noticing lasting changes in sensory experience); acceptance (confronting and processing long‑suppressed painful experiences leading to immediate shifts in felt state); self as context (accessing observer, wise, or compassionate aspects of self and feeling interconnection or expanded self‑perspective); and connection with values (reorientation toward what matters, including relationships, nature, or spirituality). The paper reproduces brief participant quotes to illustrate these processes. The authors also note convergence with neuroscientific models cited in the paper—such as proposals of a ‘‘flattened landscape’’ under psychedelics that permits transitions between mental states—and suggest that this temporary increase in neural and psychological flexibility may create a window for new habits. Early practical feedback from Psilodep 1 informed Psilodep 2 design choices: participants preferred a humanistic, non‑directive approach and therapists reported the ACE principles to be helpful when applied flexibly.

Watts and colleagues interpret their findings as convergent evidence that psychological flexibility is a central process in psilocybin assisted therapy. They argue that psychedelics may produce rapid increases in psychological flexibility—facilitating present‑moment contact, acceptance of difficult emotion, loosening of rigid self‑narratives, and renewed contact with values—and that psychotherapy grounded in the PFM can shape preparation and integration to consolidate and extend these gains. The authors position this work alongside earlier psychotherapy research showing that improvements in psychological flexibility predict therapeutic gains and that Acceptance and Commitment Therapy (ACT) can cultivate these processes; they suggest that psilocybin may accelerate or amplify PFM‑relevant change and that a PFM‑informed psychotherapy could help translate acute experiential shifts into lasting behavioural change. In discussing application, they stress that ACE is intended as a flexible, non‑directive scaffold rather than a prescriptive protocol: therapists are to emphasise acceptance, connection, and embodiment while following the patient's unfolding process. Several limitations and uncertainties are acknowledged. The evidence supporting ACE is largely qualitative and derived from an open trial with a small sample; many of the reported participant experiences are anecdotal and require replication. The authors note the general limits of talking therapies (language constraints) and the need to practise and consolidate newly established behaviours—psilocybin may open a window of flexibility, but maintaining change depends on post‑session support. They also observe that not all participants reach the behavioural change stage of integration and that further follow‑up dosing or integration may be needed to prolong benefits. On implications, the study team suggests that PFM‑based psychotherapies may be especially well suited to prepare patients to engage with challenging material and to support post‑session meaning making and committed action. The ACE model is presented as a practical bridge between a powerful inner experience and outward, value‑driven life change; ongoing trials (including Psilodep 2 and work at other centres) will be needed to test its utility and scalability.

The authors conclude that the psychological flexibility model both helps explain processes of change observed in psilocybin assisted therapy and provides a useful framework to guide preparation and integration. They propose that psychedelics can rapidly disrupt constraining patterns of thought and feeling, offering an embodied opportunity to learn acceptance and reconnect with values, while PFM‑based psychotherapy—implemented here as the ACE (Accept, Connect, Embody) model—can help translate those acute experiences into lasting behavioural change. Watts and colleagues note that ACE is currently being used in ongoing trials and express the hope that integrating PFM principles into psychedelic therapy will produce durable benefits for patients and inform future, more fully developed therapeutic models.