I don't believe what you say is true at all, this site clearly states that Dronabinol, (the synthetic form of THC used in Marinol), can create a false positive in drug tests for marijuana. This is also confirmed by another source found here. With all due respect, please don't post information you are not 100% certain is true, it only makes it that much harder to get my question answered.

So my question still stands, does anybody know if drug testing labs can know if you are using marijuana and not Marinol?