This paper provides a review of the literature on the nature, use and clinical effectiveness of MDMA-assisted psychotherapy for the treatment of patients with post -traumatic stress disorder (PTSD). We first describe MDMA, highlighting its pharmacological properties and psychological effects, followed by historical informations on its synthesis and early therapeutic uses. We will then analyse the phase III clinical study, as well as the long-term clinical evaluations of the therapy. The results show that MDMA-assisted therapy is highly effective in treating PTSD. A phase III study showed that in a 90 -participant sample, 67% of participants no longer met the diagnostic criteria for PTSD after therapy, and that 88% of participants had a statistically significant reduction in their symptoms. MDMA acts mainly at the level of emotions and social interactions, and it helps the patient to feel confident with his therapists while encouraging the expression of emotions. MDMA facilitates access to traumatic memories where, under normal circumstances, the emotional charge exceeds the subject's capacity for integration and symbolisation. In this new transitory state, the patient, supported by the presence of two therapists, can then revisit his or her traumatic experiences in order to process them with classic therapeutic tools. MDMA-assisted psychotherapy is an innovative approach that can be extended far beyond the treatment of PTSD. It is part of the rapidly developing field of psychedelic -assisted therapies, the specificity of which is a one-time intake of a substance that differs from the prolonged use of molecules with therapeutic properties in psychiatry.