question about Humaworm formula

Hi,
I consider using Humaworm to get rid of some of the freeloaders inside me. I think the blend of herbs is fantastic!
There is one thing that puzzles me though: how come the parasites do not get resistant to herbs in a 30 day period? I would think that even 15 days is a long enough period to create a resistance, considering that the dosage stays the same for the whole period (does not increase at all)!