Medicine side effects

I am interested in knowing if Albendazole, or Biltricide, or Ivermectin, or any antihelmentic should give someone side effects if it does not have a pathogen to kill.

It is my understanding that these antihelmetics only work on the insect biology or zoology, and not our human biology.

If that is true then if you took one type or another and yielded zero results then you either don't have the pathogen or you have the wrong drug for what you are trying to treat.

Then could we conclude that a parasitic infection truly exists by the fact that the die off effects occurred?

Any assistance with this with links is greatly appreciated. Tweet