I was about to say you could make a profit from selling it for more than it's worth, but then I realized that it's a profit either way because it was a gift. Carry on.
Not a druggie, but dealers do accept gift cards. Depending on their preference of the place its for, of course, and what they value it at for their goods ranges from worth half as much to almost full. If they aren't getting cash, they're going to rip you off. The more you know..
"...Why not."