Background and research question. (A) Previous studies of transcutaneous cervical vagus nerve stimulation (tcVNS) found modulated brain activity in regions associated with opioid craving and/or withdrawal. Heart rate reductions during tcVNS were also observed. The hypothesized mechanism of action is shown, where tcVNS is believed to produce afferent signaling to the nucleus tractus solitarius (NTS), followed by neural processing and resultant efferent signaling affecting peripheral organs such as the heart. (B) In this study, we hypothesized that tcVNS would reduce opioid withdrawal symptoms in comparison to sham stimulation in a double-blind, randomized, sham-controlled pilot study.