Although it is legal in the U.S. (at this point in time), that does not necessarily mean it is legal under the FFD guidelines. You need to check with your medical review officer or site NRC representative to find that out. It appears from what little I read when I goggled it, is that they don't know just yet how bad it can affect your body, but it's probably worse than the THC in cannabis. The FDA has it listed right now as a drug of concern.
If people you know are trying to circumvent the rules by using something synthetic they should just get in a line of work that doesn't have a FFD program. I know it's not worth my livelihood to play around with.