The expanding map of 33 states and the District of Columbia with legalized medical marijuana reflects an increased normalization of adult cannabis use. Legal use by adults is beginning to shift perceptions of risk among youth and adults alike, with perceptions of the harmfulness of marijuana use decreasing. Adolescent attitudes toward marijuana are becoming more positive and rates of marijuana use are rising in many states where cannabis has been legalized. Within this context, treating adolescent marijuana use is likely to become increasingly difficult and the need for more effective intervention strategies more urgent. The context in which parents are legal users of medical marijuana (MM) may pose an additional set of risks for their offspring. The proposed Stage 1A/1B treatment development research will involve a mixed-methods approach to formulating the Cannabis Actions and Practices (CAP) intervention. CAP is a parent-focused intervention to help parent MM users address adolescent marijuana use. The study will occur in two phases. In Phase I, 3 focus groups will be conducted to inform the structure, content, and context for the interventions’ delivery, to obtain feedback from parents who are currently legal users of MM, to obtain feedback from adolescents, and for dispensary personnel to obtain information about the feasibility of dispensary-supported dissemination. In Phase II, a pilot evaluation of CAP will be conducted, with 60 MM parents randomly assigned to CAP (n=30) or to a delayed CAP wait-list (WL) condition (n=30). Parents and their adolescents will be assessed at baseline and 3, and 6 months after baseline. Primary outcomes will be adolescent marijuana use and perceptions of marijuana harmfulness. Secondary outcomes will include parenting behaviors such as youth exposure to marijuana, communications discouraging adolescent marijuana use, and setting expectations. We hypothesize that CAP will be associated with significantly more positive pre-to-post outcomes, compared to the WL condition. We will also examine key targets of change, including changes in parent perceptions of marijuana harmfulness, parent monitoring, parent sense of competence, and parent behavioral intentions. The multi-method, multi-source data collection will include parent and youth report and biological urine assays. The study is designed to evaluate the promise of CAP, a novel theory-guided, empirically based, brief early intervention, for helping parent legal medical marijuana users support marijuana abstinence in their marijuana-involved adolescents.