This study examines how marijuana use affects processes related to recovery from chronic posttraumatic stress disorder (PTSD). Half the participants will be individuals with chronic PTSD and heavy marijuana use and half will be individuals with chronic PTSD and no marijuana use. This study will assess how individuals with PTSD with heavy or no marijuana use perform on a discriminative conditioning and extinction paradigm designed to measure fear extinction learning, and how they respond to a brief daily imaginal exposure treatment in regards to PTSD symptom reduction.

In this study, 36 patients with chronic PTSD and heavy marijuana use (heavy) and 36 patients with chronic PTSD and no marijuana use (no use) will be recruited to examine the effects of marijuana use on behavioral (emotional experiencing), physiological (skin conductance, acoustic startle) and biological (cortisol, blood pressure) responding on a well-established discriminative conditioning and extinction paradigm. To examine real world therapeutic implications, we will also examine how individuals with PTSD and heavy or no marijuana use differentially respond to a brief (6 session, 50 min) daily imaginal exposure (IE) treatment. Throughout treatment, we will monitor level of cannabis metabolites in urine samples of marijuana users to correlate effects to outcomes and preliminarily explore how varying levels of cannabis metabolites affect extinction processes. Independent evaluators will assess patients at baseline, 4 weeks, and 12 weeks following study entry.

Inclusion Criteria:

1. Current PTSD diagnosis based on DSM-5 criteria, with a minimum duration of 12 weeks since the traumatic event;
2. Between the age of 18 and 65;
3. Current heavy marijuana use (5+ days per week for 3+ months) or no marijuana use in the last 3 months
4. Current diagnosis of a cannabis use disorder based on DSM-5 or no current diagnosis of a substance use disorder

Exclusion Criteria:

1. Current diagnosis of schizophrenia, delusional disorder, or organic mental disorder as defined by the DSM-5.
2. Current diagnosis of bipolar disorder, depression with psychotic features, or depression severe enough to require immediate psychiatric treatment (i.e., serious suicide risk with intent and plan).
3. Unwilling or unable to discontinue current trauma-focused psychotherapy
4. Any previous experience with prolonged exposure (PE) treatment
5. No clear trauma memory or trauma before age 3
6. Unstable dose of psychotropic medications in the prior 3 months
7. Ongoing intimate relationship with the perpetrator (in assault related PTSD cases).
8. Current diagnosis of a substance use disorder according to DSM-5, other than marijuana in the last 3 months.