In 2013, Peter Oehen and colleagues published the first pilot study of MDMA-assisted psychotherapy outside the United States. The Swiss study focused on people with treatment-resistant PTSD, a group for whom previous treatments were insufficient.

Twelve participants received three experimental sessions, combined with intensive therapeutic guidance. Half received a full dose of MDMA, while the other half received a very low dose as an active placebo. Before and after the treatment, the severity of PTSD symptoms was measured using standardized instruments.

The results were encouraging, but cautious. Participants in the group that received the active dose showed, on average, a stronger reduction in symptoms than the placebo group. However, the difference was not as large as in later, larger studies. The researchers themselves noted that a dose of 25 mg, originally intended as a placebo, might already have a mild therapeutic effect.

An important outcome was that the treatment proved to be safe. There were no serious side effects, and participants indicated that the sessions—despite their intensity—were perceived as valuable. A one-year follow-up showed that some of the participants retained the benefits.

Oehen’s study constituted an important step towards the later phase 2 and phase 3 trials of MAPS. It demonstrated that the protocol was also workable in a European, non-MAPS context, and that the efficacy was not solely attributable to the American research tradition.