Posttraumatic Stress Disorders in Police, Correctional Service Officers, and 911 Operators

Inclusion Criteria: * Understands and reads French * Currently or previously worked for the Quebec City Police Department, or the 911 dispatch for Quebec City, or another police department or 911 dispatch in the province of Quebec, or for the Quebec Ministry of Public Security as a correctional service officer * Meets criteria for a trauma-and stressor-related disorder, such as: Acute Stress Disorder, Posttraumatic Stress Disorder, Adjustment Disorder, Other Trauma- and Stressor-Related Disorder, as defined by the Diagnostic and Statistical Manual for Mental Disorders, 5th edition. * The trauma-and stressor-related disorder must be due to a work-related event. * A score of at least 4 (moderately ill) on the Clinical Global Impressions-Severity Scale. * Participants who are currently taking a Selective Serotonin Reuptake Inhibitors or Selective Norepinephrine Reuptake Inhibitors (antidepressants) must accept to skip their morning dose on the days that they receive the study's intervention. Exclusion Criteria: * Systolic blood pressure \< 100mm Hg (millimeter of mercury) at visit 0. * Heart rate \< 55 bpm (beats per minute) at visit 0. * Medical conditions that contraindicate propranolol administration, as determined by the treating physician. * Previous diagnosis of a traumatic brain injury (TBI). * Previous adverse reaction or non-compliance with a beta-blocker. * Medications that can have an dangerous interaction with propranolol. * Fertile women who are not using an adequate contraceptive methods. * Pregnant women. * Nursing women. * The following psychiatric conditions: past or present bipolar disorder, past or present psychotic disorder, present substance abuse or dependence, actively suicidal, past or present neurological disorder, complex posttraumatic stress disorder.