TaVNS 8 sessions, 30 min, 4 weeks GAD: 20 Hertz (Hz) - 80 microseconds (µs) CP: 5Hz-200µs IBS: 3Hz-250µs

TaVNS will be applied by the TENS 7000 device. The stimulation was set according the group of treatment: (GAD: 20Hz-80µs), (CP: 5Hz-200 µs), (IBS: 3Hz-250µs).

The current intensity was individually established under the pain threshold .The stimulus generates an continous asymmetric biphasic waveform. Ear clip electrodes were plugged in the concha area of the left ear. The stimulation will last 30 min per session (total=8)

To assess the response effect of the TaVNS on the severity of anxiety disorders measured by the 21 items self-administered Generalized Anxiety Disorder GAD-7 questionnaire, where scoring scores of 5, 10 and 15 represent cut-off points for mild, moderate and severe anxiety. A response will be considered as a reduced cut-off point from baseline.

To assess the response effect of the TaVNS on the severity of pain and the impact of this pain on daily functioning (Interference) measured by the 9 items self-administered Brief Pain Inventory (Short Form) questionnaire; from 0 (no pain) to 10 (worst pain), ratings from 1 to 4 corresponded to mild pain, 5 to 6 to moderate pain, and 7 to 10 to severe pain with cut-off points being 4 and 6. Scoring pain severity is the mean of the total pain score out of 10. Interference from 0 (no interference) to 10 (completely interferes), rating mild (<=5), moderate (6-7), and severe (>= 8) with cut-off points being 5 and 7. Scoring the interference severity is the mean of the total Interference score out of 10. A response will be considered as a reduced cut-off point from baseline.

To assess the response effect of the TaVNS on the severity of irritable bowel syndrome measured by the self-administered Irritable Bowel Syndrome Severity Scoring System (IBS-SSS), where the maximum achievable score is 500. Mild, moderate and severe categories were indicated by scores of 75 to 175, 175 to 300 and > 300 respectively, with cut-off points being 175 and 300. A response will be considered as a reduced cut-off point from baseline.