This study is evaluating the safety and efficacy of methylone in adults with PTSD. The study is conducted in two parts.

• Part A is open-label and will enroll up to 15 participants with PTSD
• Part B is randomized (1:1:1), single-blind and will enroll up to 45 participants with PTSD

Eligible participants will enter a 3-week Treatment Period (Part A) or 4-week Treatment Period (Part B) where they will receive methylone once weekly. Following the Treatment Period, participants will enter a 6-week Follow-up Period (Part A) or 8-week Follow-up Period (Part B).

Inclusion Criteria:

• Meets DSM-5 criteria for severe PTSD diagnosis, with a symptom duration of at least 6 months.
• Tried at least one treatment for PTSD (either psychotherapy or pharmacological treatment).
• Proficient in reading and writing in local language sufficient to complete questionnaires.
• Free from any other clinically significant illness or disease.

Exclusion Criteria:

• Primary diagnosis of any other DSM-5 disorder.
• Body mass index (BMI) <18kg/m2 or ≥40 kg/m2.
• Smokes an average of >10 cigarettes and/or e-cigarettes per day.
• Uncontrolled hypertension at Screening.
• Use of prohibited concomitant medications or therapies.
• Current or previous history of clinically significant cardiovascular/cerebrovascular conditions.