Posttraumatic stress disorder (PTSD) is a disabling psychiatric disorder that affects 20%-30% of U.S. Veterans. PTSD is strongly associated with increased risk for substance abuse comorbidity, including cannabis use disorder. Multiple states now include PTSD as a condition for which patients can be legally prescribed medical marijuana, despite the fact that there has not been a single large-scale randomized clinical trial demonstrating the efficacy of cannabis to treat PTSD to date. The overall objective of the current proposal is to study the impact of reduced cannabis use on functioning among Veterans with PTSD. The investigators will evaluate the relationship between cannabis use and daily functioning among cannabis users and heavy cannabis users. The central hypothesis is that reductions in cannabis use will lead to positive changes in the functional outcomes of Veterans. The rationale for this research is that it will provide the first and only real-time data concerning the impact of reduced cannabis use on daily functioning among Veterans with PTSD.

Posttraumatic stress disorder (PTSD) is a disabling psychiatric disorder that affects 20%-30% of U.S. Veterans. PTSD is strongly associated with increased risk for substance abuse comorbidity, including cannabis use disorder; however, multiple states now include PTSD as a condition for which patients can be legally prescribed medical marijuana, despite the fact that there has not been a single large-scale randomized clinical trial demonstrating the efficacy of cannabis to treat PTSD to date. The overall objective of the current proposal is to prospectively study the impact of reduced cannabis use on psychosocial functioning among Veterans with PTSD. To do so, the investigators will first use ecological momentary assessment (EMA) methods to evaluate the relationship between cannabis use and daily functioning among Veterans with PTSD. Next, the investigators will use mobile contingency management (CM) and EMA to assess the impact of reduced cannabis use on daily functioning among Veterans with PTSD who are heavy cannabis users. The central hypothesis is that reductions in cannabis use will lead to positive changes in the functional outcomes of Veterans. The rationale for this research is that it will provide the first and only real-time data concerning the impact of reduced cannabis use on daily functioning among Veterans with PTSD. As a result, this innovative and timely project has the potential to significantly advance VHA healthcare and will directly inform the ongoing national debate concerning the impact of cannabis use on the long-term functional recovery of Veterans with PTSD.

Inclusion Criteria:

• Veteran status
• Ability to speak and write fluent English
• Current PTSD diagnosis
• Use of cannabis on 13+ days in the past month (i.e., use on 3+ days per week)

Exclusion Criteria:

Participants will be excluded if they:

• Have experienced a change in their psychiatric medication regimen during the past month (e.g., a new medication has been prescribed or the dose of an existing medication has been changed), or expect to experience a such a change during the course of the study
• Are receiving non-study CUD treatment
• Meet diagnostic criteria for bipolar disorder or schizophrenia (note that the SCID-5 (First et al., 2015) will be used to diagnoses these and other disorders)
• Become imprisoned
• Become hospitalized for psychiatric reasons
• Report imminent risk for suicide or homicide
• Meet current criteria for a substance use disorder other than cannabis use disorder or tobacco

The investigators do not plan to attend individual participant data.