Inclusion Criteria:  Participants with a current diagnosis of PTSD as defined by the CAPS-5 for DSM-5, with a CAPS-5 Total Symptom Severity Score of ≥30 at Screening and Baseline and no >25% decrease in Score from Screening to Baseline The index trauma event must have occurred in adulthood, i.e., when the participant was ≥18 years of age Suitable contraception use in line with protocol requirements Ability to swallow tablets  Exclusion Criteria:  A period of less than 6 months since the index trauma event Current and ongoing exposure to the trauma that caused the PTSD Complex PTSD Severe depression as measured by a score of ≥ 35 on the MADRS Borderline personality disorder, bipolar disorder and other psychotic disorders Use of antidepressant medications within 30 days (fluoxetine within 90 days) of Screening. The use of alprazolam, flunitrazepam and chronic daily use of other benzodiazepines within 90 day of Screening. Failed more than three trials of antidepressant medication(s) prescribed for the treatment of PTSD. Concurrent trauma-based psychotherapy such as Cognitive Behavior Therapy, Prolonged Exposure Therapy, Eye Movement Desensitization and Reprocessing Therapy. Participants may however continue to receive supportive counseling that has been in place for a minimum of three months prior to Screening. Any moderate or severe substance use disorder in the past 12 months Any clinically significant medical history or findings as determined by the Investigator that could interfere with the objectives of the study or put the participant at risk