Table 1.

Summary of included studies. (RCT = randomised control trial, Sp6, St36, CV24, LI4, St5 and P6 = acupuncture points).

Study and year	Study design	N	Stimulation parameters	Electrode position
Wong et al. 2015 [13]	RCT	96	•TENS - acupuncture (Codetron – 902-C) •Pulse width: 250 ms •Frequency: 4 Hz, Square pulses •Intensity: adjusted to produce a deep, strong, with or without mild aching, sensation at the attachment point of the electrodes. •20 min per session	Sp6, St36, LI4 (active) CV24 (indifferent)
Vijayan et al. 2014 [14]	Interventional study	30	•TENS (MEDIHIGHTEC 8000 combo) •Pulse width: 250 μs •Frequency: 50 Hz, Square pulses •Intensity: defined as the maximum intensity that the subject still perceived to be comfortable. •5 min per session	Parotid glands, bilaterally
Wong et al., 2003 [15]	RCT	37	•TENS - acupuncture (Codetron - 902-C) •Pulse width: 250 ms •Frequency: 4 Hz, Square pulses •Intensity: adjusted to produce a deep, strong, with or without mild aching, sensation at the attachment point of the electrodes. •20 min per session	Group A Sp6, St36, LI4 (active) CV24 (indifferent) Group B Sp6, St36, P6 (active) CV24 (indifferent) Group C Sp6, St5 and 6, P6 (active) CV24 (indifferent)
Lakshman et al. 2015 [16]	Interventional study	40	•TENS (model-NS Electro Pulse) •Frequency: 500 Hz, sweep of 0.5–2 Hz. •AC pulses •Intensity: defined as the maximum intensity that the subject still perceived to be comfortable. •10 min per session	Parotid glands, bilaterally
Paim et al. 2019 [17]	RCT	15	•TENS (Neurodyn II Ibramed®) •Frequency: 50 Hz •Pulse width: 250μs •Intensity: defined as the maximum intensity that the subject still perceived to be comfortable. •20 min per session	Parotid and submandibular gland bilaterally