The United States is still struggling with an opioid epidemic and high rates of opioid use disorder (OUD). Medically supervised withdrawal is an important tool in management of OUD, where opioid discontinuation occurs either directly from nonmedical opioid use or following agonist treatment. Abrupt discontinuation of chronic opioid use results in a severe, multidimensional withdrawal syndrome that includes symptoms such as aches/pain, tremors, restlessness, as well as increased pain sensitivity (hyperalgesia), and negative emotional symptoms such as anxiety and irritability. There is compelling preclinical evidence that delta-9- tetrahydrocannabinol (THC) and other cannabinoid-1 receptor (CB1R) agonists can reduce opioid withdrawal symptoms. However, direct CB1R agonist-based medications can produce adverse side effects and have demonstrated abuse liability. New research suggests that indirect agonism of CB1R through increasing circulating endocannabinoids (eCBs) is a promising strategy as it confers similar benefits with fewer undesirable cannabimimetic effects. Recently, we determined sterol carrier protein-2 (SCP-2) acts as a binding and transport protein for eCBs and we have synthesized an SCP-2 inhibitor (SCPI-1) to block eCB transport and thereby increase eCB tone. This R21 Exploratory/Developmental application will evaluate the effects of SCPI-1, a novel endocannabinoid transport inhibitor using a multidimensional model of opioid withdrawal symptoms in rats. Our Primary Aim is to evaluate whether SCPI-1 attenuates symptoms of spontaneous morphine withdrawal in male and female rats and determine whether effects of SCPI-1 are via CB1R-dependent mechanisms. Opioid physical dependence will be induced using a morphine dose escalation and maintenance procedure (opioid dependent group). Following abrupt discontinuation of morphine dosing, we will inject SCPI-1 or vehicle under blinded conditions and then assess opioid withdrawal symptoms that include: 1) somatic signs (e.g., ptosis, wet-dog shakes, grooms, hypophagia and weight loss) and food intake and body weights; 2) negative emotional symptoms of anxiety- and irritability- like behavior in the open field, elevated plus maze, and bottle brush test; and 3) hyperalgesia using the von Frey test of mechanical pain sensitivity. In addition, we will evaluate if effects of SCPI-1 on withdrawal-related behaviors are CB1R-dependent through pretreatment with the CB1R antagonist rimonabant or its vehicle under blinded conditions. Overall, this research will evaluate efficacy of SCPI-1 for treatment of opioid withdrawal symptoms and advance medications development of SCP- 2 inhibitors as a novel target for OUD. This supplement is proposed to provide additional funding support for the PI given they experienced a critical life event during Year 2 of the parent grant. The PI had a child in July of 2023 and was on maternity leave through October, pausing data collection and delaying the completion of project ...