One of the amazing things about history is that the minute after we learned to plant grain, we started making beer. It seems like from the moment we became conscious we have been searching for ways to blunt or change that consciousness. It comes up throughout history in every culture.
Which brings the question, are there any animals that seek out mind-altering substances?
Catnip?
You sometimes see chimpanzees spin around in circles till they get dizzy. While not actually a drug you can say it does in some way alter thier conciousness.
I’ve known horses with a fondness for marijuana.
Well yes but you don’t won’t to go to a party with a butch of them because they chew the reefer and hardly ever pass it around.
I read somewhere that elephants will actually stomp on fruit, then come back later to eat the fermented result.
Frugivorous birds like waxwings have been known to get loopy on fermented fruit, but I don’t think it is something they’d be likely to seek out.
Outlierrn, that was hilarious!
I’m going to blow the whistle on jaguars and sheep.
Covert surveillance operations have apparently caught the big cat chewing on ayahuasca vine. The sheep have been spotted openly and unashamedly trying to score some narcotic lichen.
And they go on horrible rampages and kill people. 
I remember seeing something on TV a few years back about some small monkey’s that hung out in a touristy/resort area (in Mexico or maybe Spain don’t remember) that would steal the patrons drinks when they weren’t looking.
my cat loved catnip, which is definitely a drug to felines.
He also loved the smell of pot, though hated the smoke. He’d always come into the room when me and my friends were smoking. He probably associated the smell with a bunch of stoners who were totally willing to pet him for hours on end 
Also my friend used to live in a house who’s owner’s dog LOVED beer. He’d literally try and knock the cup out of your hand at a party so he could lap up the spilled contents, and if we weren’t careful he’d spend the party licking the keg’s tap. Weird dog
I’ve heard it said that lab rats will normally avoid alcohol, but they can be bred to be alcoholics.
And wasn’t caffeine (or something similar) allegedly discovered by a farmer who noticed his goats acting… oddly? That could be myth, though.
A dairy farmer I know has reported that his cows especially like the damp silage from the bottom of the silo. Of course, what’s making it damp isn’t entirely water.
I started this thread earlier this year, but didn’t get many responses. But take a look at Duck Duck Goose’s link.
Or discover they can fly after waking up in a tree.
Well, they don’t seek it out, but spiders have been known to partake 
http://www.youtube.com/watch?v=sHzdsFiBbFc
I know I’ve seen some monkeys drinking some fermented fruit/nectar concoction on the Discovery channel before.
And for more domesticated animals, my SO’s ferrets and my pet bunny will drink/spill any strawberry daiquiri you happen to leave lying aound.
ETA: ‘smoking monkey’ search on youtube posted this video as #1 result, which I found entertaining. 
Smoking monkey
“…everybody must get stoned.”
-Bob Dylan-