Transcutaneous Electrical Nerve Stimulation (TENS) is a method of electrical stimulation which primarily aims to provide a degree of symptomatic pain relief by exciting sensory nerves and thereby stimulating either the pain gate mechanism and/or the opioid system. The effectiveness of TENS varies with the clinical pain being treated, but research would suggest that when used 'well' it provides significantly greater pain relief than a placebo intervention. There is an extensive research base for TENS in both the clinical and laboratory. It is worth noting that the term TENS could represent the use of ANY electrical stimulation using skin surface electrodes which has the intention of stimulating nerves. In the clinical context, it is most commonly assumed to refer to the use of electrical stimulation with the specific intention of providing symptomatic pain relief.
The type of stimulation delivered by the TENS unit aims to excite (stimulate) the sensory nerves, and by so doing, activate specific natural pain relief mechanisms. For convenience, if one considers that there are two primary pain relief mechanisms which can be activated the Pain Gate Mechanism and the Endogenous Opioid System, the variation in stimulation parameters used to activate these two systems will be briefly considered. Experts generally consider TENS to be safe, although the machine could cause harm if misused.