Definitely don't take it on a flight. If they deem anything about you or your bag suspicious (even completely unrelated to N) they could search, or they could just select you for a random search. In the US at least, there is some anecdotal evidence that many TSA officers only care about security threats and might just let it go, but this is based mostly on stories I've seen about people carrying relatively small amounts of cannabis, so it may or may not apply to N. Since it wouldn't have to clear Customs, mailing it should be relatively safe. I know some cross country mail, at least in the US and Canada, gets put on commercial flights and I'm not sure what kind of screening it goes through first so the best option may be a ground service from UPS, FedEx, etc.