I'd say absolutely NO. No federally "illegal" drugs are allowed on any cruise ship, "medicinal" or not.
That's not to say that I haven't smelled an "unusual" odor on a cruise, but if you're caught you'll be in serious trouble!
You may find yourself in a jail in a foreign port , or you may be thrown off the ship to find your own way home.
IMO, don't try it!
"A truly happy person is one who can enjoy the scenery on a detour."
I wouldn't advise trying it either. I've read occasional stories of people who were deported from the ship into the hands of the police at various ports -- not a pretty situation.
Also, when you disembark from the ship, the customs agents do use dogs. All the luggage is lined up in rows so that their furry, 4-legged agents can walk between the suitcases to detect any unusual items. Not worth it in my estimation.