Substances can happen.
They can be found anywhere, not just where they are legal.
I have smelled wacky tabbaki on a couple of cruise but since it did not envolve me, there was no problem.
Carnival Liberty New Year's Eve 2007
Liberty of the Seas 5/2008+11/2009
Allure 1/16/ 2011
Independence of the Seas 12/29/2013 Top-notch!