@Steve Drew,
I don't know whether this alleged herbal blend will give you a false positive on your drug test but if you're actually honest here in terms of your not using drugs then at least if you do come up false positive, I do legally you have the right to appeal any drug test that is a false positive.
Keep away from this herbal blend until its out of your system so by the time you have to take a second drug test then you're boss or whomever is giving you the drug test will see that you've been clean from drugs even before the first drug test and that the false positive results from the first test were basically an error on their part.