Before you buy any supplement you need to make sure that it has been 3rd party tested! Third party testing is test carried out by a company other than the one selling or manufacturing it.
This testing ideally will confirm that the product is free from impurities such as
METALS
MOULDS
PLASTICS
PESTICIDE RESIDUE
Even if something’s certified or organic, that does not mean its free from or has been tested for all these impurities (toxins). These impurities accumulate in your body and they can feed the parasites and even have negative effects in your body (even if you don't have parasites).
If you're shopping for supplements, always check that it has been third party tested to be free from these impurities so you know exactly what you're getting.