The purpose of this study is to test whether propranolol is capable of reducing subsequent physiological trauma-related conditioned responses, as well as self-reported post-traumatic stress disorder (PTSD) symptoms.

Inclusion Criteria:

• Suffer from chronic PTSD for at least 6 consecutive months;
• Obtain a score of 33 or more on the Impact of Events Scale-Revised:
• For participants aged 40 years: accept to undergo an electrocardiogram assessment. The results of the electrocardiogram must be normal;
• Accept to not commence taking new medications on a regular basis during the study.

Exclusion Criteria:

• Hypotension;
• Cardiac rhythm below 55 beats per minute;
• Medical conditions that contraindicates the administration of propranolol;
• Previous adverse reaction to, or non-compliance with, beta-blockers;
• Current use of medication that may involve potentially dangerous interactions with propranolol;
• Any medication that can have an impact on cardiac rhythm;
• Women who are breast feeding;
• Past or present bipolar disorder or psychosis,
• Present substance abuse or dependence, suicidal ideation;
• Participating in psychotherapy other than support psychotherapy;
• An average score above 20 on the Dissociative Experience Scale.