Can TENS machines be used by everybody? TENS machines tend mainly to be used to help reduce pain from problems in muscles, joints and nerves (so-called musculoskeletal pain). They may work better for these problems than for tummy (abdominal), chest or head pains. Unlike a lot of medication there are virtually no side-effects when using a TENS machine. However, people with the following must not use a TENS machine: When the cause of the pain is not known or is not diagnosed. 1.Pregnancy (unless specifically medically advised - or in labour). 2.Pacemakers. 3.Epilepsy or certain types of heart disease.