The zapper has no side effects
It has some side effects when it does not manages to kill parasitic worms because the parasitic worms will try to avoid the strong curent paths and this will produce irritations, cuts/holes, internal bleeding, inflammation in the body. This can be a huge problem when parasitic worms move in the head area, near the eyes, near the hears, near the brain.
Without l ascorbic acid i would probably be dead.
From my experiments, zappers are inefficient and can be dangerous if you are infected with a kind of parasitic worm which can move to others parts of the body and survive in this other part of the body (for example toxocara larvaes, Tapeworms larvaes, Ascaris larvaes)
The idea of using an electric current to kill parasitic worms is good, but unfortunately in its current state, it does not work, it may help to control a bacteria overgrowth but that's all.