Summary: ∆8-THC is a minor cannabinoid found in the cannabis plant, possibly as an artifact resulting from non-enzymatic isomerization of a small amount of ∆9-THC. Outside of the plant, ∆8-THC can be easily synthesized from CBD. As a result of federal and state policy changes, the Agriculture Improvement Act of 2018, and the absence of clear guidance on the control status of ∆8-THC, manufacturers have produced large supplies of this cannabinoid, which is now available to the public everywhere unregulated, in spite of clear warning from the CDC and FDA to the possible risks of consuming ∆8-THC containing products. The synthetic process of converting hemp-derived CBD to ∆8-THC results in several impurities in the marketed products. Our group has identified 15 impurities, eight of them with no known pharmacological properties. The goal of this proposal is directed toward the isolation and characterization of these impurities in sufficient supply to study their pharmacology and their interaction with ∆8-THC. This will be achieved through the following set of specific aims: Aim 1: To scale up the isolation process for ∆8-THC products' impurities to prepare enough supply for both in vitro and in vivo evaluation. Aim 2: To assess the affinity, potency, and behavioral effects of ∆8-THC products' impurities. This will be carried out using in vitro assays to study the binding affinity of each impurity to human CB1, CB2, and GPR55 receptors. Efficacy and potency will be evaluated using functional GTPγS and/or cAMP assays as well as calcium mobilization assays in cultured neurons. Further, in vivo testing of impurities' effects on body temperature, locomotion, catalepsy and nociception will be evaluated in cohorts of male and female mice (tetrad assay). Aim 3: To determine whether ∆8-THC impurities can potentiate, antagonize, or be additive to the psychoactive effects of ∆8-THC through both in vitro and in vivo studies. Our team has the necessary expertise to achieve these goals. At the conclusion of this work, we will have a good understanding of the pharmacology of these impurities and how they influence the effects of ∆8-THC.