So why does psilocybin appear to be a more successful treatment for depression than a typical antidepressant? Brain imaging data from the trial, alongside the psychological data we collected, appears to show that while SSRIs dampen emotional depth by reducing the responsiveness of the brain’s stress circuitry, helping to take the edge off depressive symptoms, psilocybin seems to liberate thought and feeling. It does this by “dysregulating” the most evolutionarily developed aspect of our brain, the neocortex. When this liberation occurs alongside professional psychological support, the most common outcome is a renewed breadth of perspective. Psychedelic therapy seems to catalyse a type of psychological growth that is conducive to mental health, overlapping in many respects with spiritual growth.

The most exciting aspect of this trial is a sense that we are on the verge of a paradigm shift in mental healthcare linked to an improved understanding of the origins of depression, and how we can most effectively treat it. In my view, this shift will take us away from an outdated and myopic “drug-alone” perspective that has dominated psychiatry for several decades, and towards a multi-level “biopsychosocial” model. This model sees the symptoms of depression as an adaptive response to adversity, with decipherable – albeit complex – psychosocial causes. Psychedelics can treat depression by activating powerful brain states that have evolved in humans to catalyse deep psychological change. When these “hyper-plastic” states are combined with a nurturing environmental context, defensive habits of mind and behaviour can undergo a healthy, potentially enduring revision.