The rapidly changing landscape of cannabis policy in the United States is well known, but often overlooked is that legalization has made high-potency products more available. State-regulated cannabis markets offer access to cannabis products, such as concentrates with THC potencies (70-90%) that far exceed cannabis that has been sold on the black market over the last 20 years (4-12% THC potency). State reporting suggests that concentrates are commonly used and quickly rising in popularity, with increases in 2014-2019 sales (409%) far outpacing that of flower (80% increase) and edibles (234% increase). Recent data indicate that concentrate users exhibit higher plasma THC levels than flower users and a large body of research has demonstrated dose-response relationships between increasing cannabis consumption and poor mental health outcomes. Given the increasing prevalence of concentrate use, it is imperative to clearly understand how these increasingly popular, high-potency cannabis products affect mental health and psychosocial functioning. This project leverages an ongoing, longitudinal twin study, with participants assessed approximately every 5 years since adolescence. Thus, this project is a unique opportunity to rigorously test critical hypotheses about how high-potency concentrates affect psychopathology and psychosocial functioning. The Aims of this research are: Aim 1: Examine how the use of different cannabis products relates to cannabinoid exposure (e.g., THC). We will test whether the use of high-potency cannabis concentrates, compared to flower products, is associated with elevated cannabinoid exposure. We hypothesize that associations will not be explained by familial confounds (via co-twin comparisons) and individual differences (via repeated assessments). Alternatively, it is possible that concentrate users titrate to reach the same effect as flower users. Aim 2: Examine how the use of different cannabis products relates to mental health and psychosocial functioning. It is plausible that individuals vary in their propensity to use high-potency concentrates. Thus, we will examine how use of high-potency concentrates relate to mental health while accounting for familial and individual confounds, like genetics and prior substance use. We hypothesize that twins who uses more high- potency concentrates will tend to have greater levels of depression, anxiety, and impulsivity and psychosocial dysfunction compared to their co-twins who use flower or who use high-potency concentrates less frequently. Aim 3: Test whether different levels of cannabinoid exposure are associated with mental health and psychosocial outcomes. We will test how different levels of cannabinoid exposure (i.e., THC-COOH concentrations in whole blood) associate with depression, anxiety, and impulsivity as well as psychosocial functioning. That is, we will directly test the hypothesis that cannabinoid exposure is associated with mental health and psychosocial functioning...