Exploring Mechanisms of Massed Cognitive Processing Therapy

Inclusion Criteria: Are fluent in English * Have experienced a Criterion A traumatic event during their lifetime * Have a PTSD diagnosis verified via the Clinician Administered PTSD Scale for DSM * Are interested in receiving evidence-based treatment (CPT) for PTSD and able to attend either 10 therapy sessions over the course of one week (5 days) or are interested and able to complete 5 relaxation training sessions over the course of one week (5 days) * Are willing and able to complete self-report measures and clinician-rated assessments at multiple time points over the course of the study * Reside in the state of Illinois during the course of treatment Exclusion Criteria: 1. The traumatic event occurred in the past month 2. They are currently suicidal or homicidal (i.e., plan and intent) 3. They have unmanaged psychosis or mania 4. They have not been on a stable dose of psychotropic medication for at least one month by the time of the baseline assessment 5. They have completed an evidence-based cognitive behavioral PTSD treatment (e.g., Cognitive Processing Therapy or Prolonged Exposure) in the past 3 months or are currently receiving an evidence-based PTSD treatment 6. They have an intellectual disability or significant cognitive impairment that would prevent them from engaging in CPT 7. They have a serious or unstable medical illness or instability for which hospitalization may be likely within the next year 8. They have an active substance use disorder (within the past 3 months) that would require immediate medical observation if substance use was discontinued (i.e., potential lethality) 9. They are involved with current legal actions related to the traumatic event that is anticipated to be targeted during treatment 10. They have a visual or auditory impairment that would prevent them from fully participating in study activities 11. Subjects who, at the time of consent, appear to have extenuating life circumstances (e.g., unstable housing, no internet access, etc.) which, in the judgement of the Principal Investigator, could affect the ability to deliver the intervention with fidelity