“Transcutaneous electrical nerve stimulation” (TENS) devices work to temporarily relieve pain by delivering pulses of low- volt electrical currents through the skin to activate nerves and stimulate the release of endorphins (pain-blocking chemicals in the body). While physical therapists have long been trained to use these devices in professional settings, the FDA approved the first over-the-counter TENS device in 2004. However, TENS devices sold directly to consumers do not undergo rigorous study to prove they relieve pain. Much of what is known about TENS and arthritis pain relief comes from studies of devices that are designed for, and applied by, healthcare professionals. While these studies have yielded conflicting results, many show that TENS failed because the therapy was not performed correctly.