Alcohol is a type of organic compound featured in MS Paint Adventures that causes intoxication and can be consumed in beverages. Hangovers are a common after-effect of the consumption of alcohol.
In Problem Sleuth it is a commonly found item. Alcohol provides a large boost in Imagination, and is found in a variety of shapes, sizes and potency. Its primary use is to allow characters to enter the Realm of Imagination by imbibing liquor and then entering their Fort.
Problem Sleuth is the only character known so far to suffer from hangovers. While under the status of a hangover, Problem Sleuth's Imagination lowers, but it's maximum level remains the same. His Vim however, takes a hit from the loss of steadiness. Hangovers can be removed by drinking coffee, particularly cold coffee, which also may restore some Vim, correcting him to his pre-Hungover state.
Ace Dick had a Cruet of Brandy stashed under the desk in his office as well.
Pickle Inspector had a bottle of Illicit Moonshine in his office. The bottle was too big to fit under his desk.
AD brewed up some Candy Corn Liquor in the Still Room. This liquor was so potent it granted Pickle Inspector god-like powers in the Realm of Imagination.
Mobster Kingpin, being diabetic, exclusively drinks Sugar Free Candy Liquor. It was potent enough to grant him demon-like powers in the Realm of Imagination.
Potent Grain Alcohol fuels Ace Dick's Generator which, in turn, powers his window.
Homestuck, with its mainly underage cast, doesn't feature as much alcohol as Problem Sleuth did. However, Rose Lalonde's mother is a very heavy drinker and is never seen without a martini in her hand. Rose can tell when her mother is around by the ubiquitous presence of liquor bottles. Rose later finds that her mother has left her martini glass behind when Rose arrived at the Land of Light and Rain, and decides to sip it thoughtfully, immediately spitting it all out. The post-Scratch version of Rose's Mom, Roxy Lalonde, has a similar drinking problem, although she quits after entering the B2 session, but eventually relapses after entering Trickster Mode.
Two years into travelling through the void, Rose takes a taste for liquour - due to nervousness for her meeting with Kanaya Maryam. Though it causes her to miss the official start, it somehow becomes a date, they kiss, and Rose falls down the stairs. In Act 6 Intermission 5, during a talk with Karkat about Terezi, Dave mentions Rose, suggesting that she became an alcoholic after the incident.