It is a generally widespread consensus that persons with organ/tissue transplants should NOT use ionic foot spas at all. The reasoning behind this, is that a transplanted organ/tissue is technically not part of your body and could be identified as an “invader” by the ions which would try to “fix” the organ/tissue by attempting to flush it out. For that reason, it is strongly recommended that persons with organ/tissue transplants NOT use the ionic foot spa unless under close physician supervision.
The second category of persons who should possibly NOT use ionic foot spas are person with “electrically active” implants such as pacemakers, defibrillators, spinal stims, etc. Again, it is strongly recommended that persons with these implants NOT use the ionic foot spa unless under close physician supervision.
Inert transplants (nonelectrical) in the body such as metal pins, screws, rods, joints (hip, knee, etc) are just fine and persons can use the ionic foot spa without issues.