According to L.A. Paul, undergoing an experience is transformative if we learn something we cannot learn without having the experience and if it substantially changes our point of view. While the implications of transformative experiences have primarily been discussed in the context of rational choice, their underlying concept has also proven fruitful in the context of unchosen occurrences. The present paper examines mental disorder and its treatment from a transformative experiential perspective, using major depressive disorder as an exemplary case. It (...) shows that developing a mental disorder typically requires a transformative experience since the two popular mental disorder classification systems primarily classify such disorders on an experiential basis. This provides an explanation for the lack of understanding mentally disordered people often face: their experiential state is epistemically inaccessible for those who have not experienced a similar state before. Furthermore, successful treatment of mental disorder again requires a (personally) transformative experience that results in the disorder’s overcoming. The paper examines pharmacological, psychological, and psychedelic-assisted treatment and reveals that each of them uses a different transformative route to recovery: a finding relevant, for example, to ongoing debates in medical ethics about informed consent. (shrink)