People with any electronic or metal implants like pacemakers, spinal cord stimulators and in-dwelling pumps should not use TENS devices. However, they are safe for people with certain health conditions. It's still best to check with your physician first, especially if you are pregnant or have cancer, diabetes, epilepsy and cognitive impairment. People allergic to adhesives or nickel should also use a hypoallergenic alternative.
Never use a TENS device while in the shower or near water. Also, avoid using it with cold packs or heating pads. It is ideal to start your TENS session when you’re awake, too. Lastly, do not stick it close to an open wound or damaged skin as it can prolong recovery time.