Are there any ill-effects from using EMS stimulation over long periods of time?

The FDA has cleared all Slendertone EMS products for sale in the US as Class II medical devices and they are safe and effective for their intended purpose (muscle conditioning or strengthening and toning).  The long-term effects of EMS muscle stimulation are not known, however, this type of technology has been used by physical therapists and doctors all over the world for over 50 years.