Upright Citizen’s Brigade had “Little Donny Disease” (magnimus- obliviophallocytis).
Strangers With Candy had the drug “Glint”, a kind of neon green slime that was administered to the lips. It seemed to cause lots of energy and hallucinations.
From the City of Heros/Villains games, there’s The Will of the Earth, a “semi-sentient bacterial sludge” that turns everything it infects into “The Devouring Earth”; a sort of genocidally hostile ecology.
There’s also the weaponized, Mad Science fortified version of the above, The Force of the Earth.
Glitterbright, a highly addictive and destructive narcotic drink from the Doc Sidhe novels.
There’s the Doctor, a sentient and generally helpful sentient “disease” from the Sector General novels.
The American Playhouse production of John Cheever’s The Shady Hill Kidnapping was punctuated with mock advertisements for “Elixorcol, The True Juice of Youth”. (I’m guessing at the spelling.) Celeste Holm was the celebrity pitchwoman. “When you look in the mirror, is your face rucked and seamed with alcoholic and sexual excesses?..Then you need Elixorcol.”
Polite Dissent has a ridiculously thorough database of fictional comic drugs here
a few highlights:
*The Dark Tower * series by Stephen King has devil-weed.
Tick, from Path of the Fury/In Fury Born. It increases reflex speed somewhat, but increases the speed of the user’s thought processes enormously. So everything they do, even at the fastest speed they can manage, is under conscious control instead of just reflexes, with plenty of thought behind it.
That reminds me of Bill Cosby talking about cocaine. He said he asked a coke-using friend, “What does it do for you?” and the friend answered, “It enhances your personality!” To which Bill replied, “Okay. What if you’re an asshole?” 
(Only time I’ve ever heard Cosby use profanity, and it was that much funnier and more effective for its unexpectedness.)
Uh, I don’t know about that…(but then, I’ve never seen the episode in question…)
Terry Pratchett is pretty good at this:
NANNY OGG: Well, that cow’s got Red Bugge, if I’m any judge
GASPODE: I’ve even got Licky End, and you can only get that if you’re a pregnant sheep.
There are probably others.
Hobbits, of course, smoke “pipe-weed.”
Why do you think they eat six meals a day? 
In Brian Daley’s 1979 S&S novel Starfollowers of Coramonde, there was a vision-inducing drug called “dreamdrowse.”
From the same universe: “Tree-of-life,” which will turn any hominid (of the right age) who eats it into a Pak Protector.
Alan Dean Foster’s Flynx novel Bloodhype involves a deadly addictive drug of that name, a/k/a “Jaster.”
You don’t want to sell me Death-Sticks.
Another from Pratchett: Slab, a mixture of ammonium chloride and radium, which will cause a troll to “sit in a corner to watch the colours.”
I recall a Freak Brothers story, “Drug Czar Freddie,” where Fat Freddy rallies public opposition to the nonexistent-even-within-the-story drug Squeak. He gets government funding for the anti-Squeak campaign, sets up an office and puts inner-city kids to work, the PTB are talking about running him for mayor . . . I won’t spoil it.
Coincidentially, The Onion AV Club this week has a list of fictional drugs: Don’t Bogart That Jenkem!
In Holly Black’s book Valiant, there’s a drug called Nevermore that allows fairies to be around iron and humans to use glamours. It also gets humans high. They call it Nevermore, because you (humans) go crazy if you take too much.
From Serenity, we have Paxilon-6 Hydrochlorate, which causes 99.9% of people exposed to it to become completely passive to the point where they literally just lay down where they are and wait to die.
What it does to the rest of the people is much worse, of course.
Babylon 5 has Stims, which are basically like caffeine shots, injected into the arm. Station medical chief Dr. Franklin had a bad addiction to them for a while on the show.
Another B5 drug is Dust, which can give mundanes temporary telepathic powers, but without any of the coping abilities that telepaths develop naturally. Most users end up rather psychologically traumatized when exposed to the thoughts and memories of others (one guy scanned a woman who had been in a skiing accident, and ended up laying on the floor screaming that the mountain was falling on him).
It’s not really a pleasure cruise for the person who gets their mind invaded by the Dust user either.
As for diseases, in the film Johnny Mnemonic, Nerve Attenuation Syndrom (NAS), also known as The Black Shakes, is a nervous disorder caused by overexposure to electromagnetic radiation coming from the omnipresent technology seen everywhere.
The computer game Wing Commander IV (and the tie-in novelization) included a plotline where the bad guys started attacking planets with a bioengineered virus that would target anyone not fitting a certain genotype, and turn their immune systems on their bodies. The end result was widespread death and decay, with most of the rest of the population being highly vulnerable to secondary diseases from poor containment/disposal of the bodies and PTSD/Survivor’s Guilt-related problems
Swamp dragons are prey to an amazing variety of diseases and disorders that run the gamut all the way from Abated Heels to Zigzag Throat.
Shifting gears considerably, in Jack Vance’s Demon Princes pentalogy Cluthe[sup]1[/sup] is something between a poison and a disease, used to kill in Star King and The Face with quite different effects (maybe the dose was different or the drug fresher).
[sup]1[/sup]An excellent piece of authoring in the linked article, by a gifted writer at the top of his game.
The White Plague also is another name for tuberculosis.
Comedian Robert Klein did a mock public service announcement promoting research into “Juergen’s myasthenia, a dreaded disease in which the nose mysteriously slides off.”
“There is no cure…but there’s HOPE!!!”