Background: Cannabis use and cannabis use disorder (CUD) are increasing in the US population, and adults aged 50 and older are among the fastest growing groups of cannabis users. While cannabis use is increasing, it is often perceived as harmless and marketed to patients as helpful for several conditions despite a lack of evidence. There is no data on past month cannabis use, daily cannabis use, and CUD among Veterans using primary care, but there is evidence that cannabis use is common in specific Veteran subgroups (11% to 25%) and that CUD identified using administrative data is increasing. Significance: There are reasons to be concerned about the potential under-identification of cannabis use among Veterans. Smoking cannabis is the most common form of cannabis use among Veterans, and there is evidence that cannabis use is associated with respiratory symptoms and cancer. Comorbid mental health conditions are prevalent among Veterans, and these conditions are commonly reported as motivation for regular cannabis use. Cannabis use negatively impacts treatment outcomes of Veterans with anxiety, depression, and post-traumatic stress disorder (PTSD), and use is associated with psychosis and suicidal ideation. Symptoms of cannabis withdrawal can frequently be confused with symptoms of mental health conditions by patients which can perpetuate use. Finally, there are effective behavioral treatments available for CUD and several medications that have shown benefit in treatment of CUD and withdrawal from cannabis in trials. It is important to identify cannabis users to ensure access to effective therapies. Innovation and Impact: This proposal will address important gaps in the priority areas of women’s health, substance use disorders, and mental health. This proposal will lay the foundation for the validation of a simple, frequency-based screening measure for cannabis use that could be feasible in the primary care setting. Specific Aims: We propose to improve our understanding of at-risk populations and determine whether cannabis treatment services in the Veteran population are being underused. We also propose to determine if certain use patterns are associated with adverse mental and physical health outcomes, placing individuals at higher risk. Such individuals (if identified) may also require brief intervention, referral, and/or treatment. Aim 1: To examine the patterns of cannabis use (past month use, daily use, CUD, persistent use), behaviors (e.g., alcohol use) associated with use, and characteristics associated with use among a nationally representative sample of Veterans 50 and older who receive VA primary care. Aim 2a: To determine whether Veterans discuss cannabis use with their providers and whether providers document use and/or intervene upon use or CUD. Aim 2b: To explore provider experiences assessing cannabis use and initiating CUD-related treatment and referrals in the primary care setting. Aim 3: Using the cohort created in Aim 1, we w...