I've used the TENS unit now for just under a year. I have never had any complications from using it. I use it on my feet which are totally numb and most always burning. I crank it all the way up - and I can barely feel it. I occasionally use it on my hands as well. This is a totally different situation - I can really feel it and it does make my fingers dance. Sometimes it is more effective than other times. My insurance paid for it and pays for all the supplies. The company sends me an order sheet monthly and I just check off what I need (if anything). It was prescribed to me by a physical therapist.