RecruitingEarly Phase 1Drug trialRM1 Project 1 - tAN NaloxoneThis two-visit, randomized, double-blind, sham-controlled trial, uses a novel naloxone blockade model in 136 individuals to determine whether the analgesic effects of a 30-minute transcutaneous auricular neurostimulation (tAN) intervention are mediated through a release of endogenous opioids. Analgesic effects of four various stimulation interventions will be measured (auricular vagus, auricular trigeminal, combination, or sham) while varying the type of intravenous (IV) infusion (either naloxone or saline) a participant is administered to determine whether the analgesic effects are mitigated by pharmacological opioid receptor blockade.