Quote Originally Posted by Burnt Toast
There is no concrete evidence establishing that zinc has any effect on THC metabolites.
Burnt Toast is right, also taking to much Zinc can cause Zinc toxicity, which is bad.

HightTimes also wrote about this and said this,
there still remains little evidence disputing the notion that self-administration of zinc supplements interferes with carboxy-THC detection since, to date, no study seeking replicating the methods employed by SUNY research team has been conducted.
source: The Truth About Zinc and Drug Tests | High Times