Transcutaneous Auricular Vagus Nerve Stimulation for Poor Weight-Loss Response to Incretin Receptor Agonists

Participants will receive active transcutaneous auricular vagus nerve stimulation plus tirzepatide 5 mg for 12 weeks. Active stimulation will be delivered to the bilateral cymba conchae, an auricular region innervated by the auricular branch of the vagus nerve. Stimulation will use an intermittent waveform of 15 seconds on and 5 seconds off at 20 Hz, with a pulse width of 0.2 ms. Stimulation intensity will be titrated from 0 mA to a level that produces mild tingling without obvious discomfort, usually 1.0-2.5 mA. Stimulation will be administered twice daily for 30 minutes per session, 5 days per week, for 12 weeks. Tirzepatide will be administered as a subcutaneous injection once weekly.

Participants will receive sham stimulation in addition to tirzepatide 5 mg for 12 weeks. Sham stimulation will be applied to the bilateral tail of the helix, an auricular site without vagus nerve distribution, whereas active taVNS targets the cymba conchae, which is innervated by the auricular branch of the vagus nerve. The sham group will use the same waveform parameters, stimulation intensity titration, and treatment schedule as the active group, namely twice daily for 30 minutes per session, 5 days per week, for 12 weeks. Tirzepatide will be administered as a subcutaneous injection once weekly.