In the past, TENS units for home use were available only through a physical therapist or other clinician. The units have been simplified, and you can now buy one without a prescription. According to Cleveland Clinic physical therapist Kelly Kinsey, PT, "The old units that came through physical therapists could be set to meet individual needs. The parameters could be altered and varied for comfort and changed to address different types of pain." The simplified TENS units you get without a prescription are not as customizable. They are programmed to the most commonly beneficial settings and comfort level.