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Reflecting on the State of the Science of Prolonged Exposure Therapy

Carmen P. McLean & Edna B. Foa

May 13, 2024



Prolonged Exposure Therapy (PE) is a trauma-focused cognitive behavioral therapy that was developed in the 1980s by Edna Foa and colleagues to treat posttraumatic stress disorder (PTSD). Building on work by Terence Keane and others testing exposure therapy with veterans with PTSD, Dr. Foa developed and began systematically testing the effects of PE among women with sexual assault-related PTSD. The early success of the treatment, along with a rigorous provider training model, led to additional trials being conducted by independent research centers in North America and later in many other countries including Sweden, Israel, Netherlands, Australia, and Japan. 


For decades, PE has been the most well-supported treatment for PTSD. A recent count identified 40 randomized clinical trials of PE with adults, and there are countless more studies using other research methodology or targeting younger persons. Unsurprisingly, PE has consistently been identified as a first line treatment for PTSD in all major clinical practice guidelines, including the ISTSS guidelines. The PE therapist manual, which was updated in 2019, has now been translated into 10 languages: Japanese, Korean, Swedish, Polish, Spanish, German, Chinese, Norwegian, Russian, and Italian. 

What is PE?

PE is a trauma-focused cognitive behavioral therapy that is typically delivered in 8-15 individual weekly or twice weekly sessions. Sessions focus on psychoeducation, in vivo exposure (i.e., approaching trauma-related feared situations in real life), and imaginal exposure and processing (i.e., revisiting in imagination and recounting aloud the memory of the worst traumatic event followed by a discussion of the recounting experience). While the therapy itself has not changed substantively since its development, the breadth and strength of evidence that has accrued in support of the effectiveness of PE over the past thirty years has significantly improved our understanding of how to treat individuals with PTSD.

Research on PE

Studies have shown that PE can significantly reduce PTSD symptoms (and typically symptoms of associated psychopathology such as depression) across several populations, trauma types, and in the presence of comorbid conditions (e.g., depression, substance use). Research in this vein has found that PE is effective even among populations with PTSD that were once thought to be poor candidates for exposure therapy. For example, when the comorbid condition is concurrently managed, PE has been found effective for individuals with comorbid substance use disorders, borderline personality disorder, and psychotic disorders. 


Over the past 10-15 years, much of the research on PE has focused on two important questions: 

  1. How can we make PE more accessible?
  2. How can we make PE more effective?

How can we make PE more accessible?

Only a subset of individuals with PTSD are likely to access standard weekly PE sessions at a specialty mental health clinic. In recognition of this, recent research has evaluated the effects of PE when delivered in briefer sessions (60-minute versus the standard 90-minute), in massed or intensive formats (e.g., daily session) through telehealth or a web-based program, and in a brief format adapted for primary care settings. The more options there are for how individuals can access PE, the more likely it is that they can find a PE program that meets their needs and preferences. 

How can we make PE more effective?

Research examining augmentation strategies has aimed to make PE more efficacious and/or more efficient by either enhancing the therapeutic learning that occurs during PE or increasing tolerability of and engagement with PE. This work includes studies evaluating pharmacological (e.g., d-cycloserine, ketamine, cannabinoids), hormonal (e.g., estrogen), behavioral augmentation (e.g., exercise, peer support), and transcranial magnetic stimulation. Despite some promising findings from animal research and experimental studies, very few candidate augmentation strategies have yet to advance to multiple randomized controlled trials among individuals with PTSD. Future research that can identify strategies to promote engagement, limit non-response, and/or improve clinical outcomes is needed to push beyond the (already high) efficacy ceiling for PE. 


The impressive body of research supporting PE was built by researchers around the world, each designing studies to answer critical scientific questions about the safety and efficacy of PE in new populations, new settings, and in novel formats. This work has and continues to challenge assumptions about who can benefit from PE, who can deliver PE, how PE sessions should be spaced and packaged, and more, with each study opening the door to a new set of scientific questions. Indeed, there remains much to learn about the use of PE and the mechanisms underlying its efficacy. There is also considerable room to improve both access and clinical outcomes. Reflecting on the state of the science to date, we are inspired and hopeful that future empirical and theoretical work will yield further insights to make PE event better, faster, and available to more individuals with PTSD.

Discussion Questions

  1. What characteristics of PE do you think have facilitated or limited its dissemination and implementation?
  2. What do you see as the most promising or important avenues of research to pursue related to PE?

Author Biographies


Carmen P. McLean, Ph.D. is a licensed Clinical Psychologist at the National Center for PTSD's Dissemination and Training Division at the Palo Alto VA and a Clinical Professor (Affiliate) at the Department of Psychiatry and Behavioral Sciences at Stanford University. Her reseach examines ways to increase the reach of exposure therapy for PTSD by addressing implementation barriers and testing digital exposure-based interventions with the goal of helping more individuals with PTSD benefit from effective treatment. Connect with Dr. McLean on X (formerly known as Twitter) at @CarmenMcLeanPhD.



Edna B. Foa, Ph.D. is a Professor of Clinical Psychology in Psychiatry at the University of Pennsylvania and Founding Director of the Center for the Treatment and Study of Anxiety. Dr. Foa has devoted her academic career to study the psychopathology and treatment of anxiety disorders, primarily obsessive-compulsive disorder (OCD) and posttraumatic stress disorder (PTSD) and is currently one of the world leading experts in these areas. Her work has been recognized with numerous awards and honors, including: Lifetime Achievement Award presented by the International Society for Traumatic Stress Studies; 2009 Lifetime Achievement Award presented by the Association for Behavior and Cognitive Therapies, TIME 100 Most Influential People of the World, and 2010 Lifetime Achievement in the Field of Trauma Psychology Award from American Psychology Association. 

Read the full paper here in JOTS

McLean CP, Foa EB. State of the Science: Prolonged exposure therapy for the treatment of posttraumatic stress disorder. J Trauma Stress. 2024 Apr 23. doi: 10.1002/jts.23046. Epub ahead of print. PMID: 38652057.