I have used a variety of Clark's zappers for years and have found that I need to use them along with other supplements for them to be most effective. For parasites I would use the device while taking parasite killing herbs. For Lyme I used the zapper for long periods and took homeopathic drops for mixed spirochetes. For the lingering viral problem I've had lately I'm zapping and using homeopathic drops for viruses. A zapper won't help with low Vitamin levels or autoimmune problems. It will not kill most intestinal parasites.
Hope this helps.