"Whiskey. Tennessee whiskey, Spock. You care for a little snort?"
Alcohol (chemical designation ethyl alcohol or ethanol) was a colorless, liquid chemical, usually the by-product of fermenting sugar. Alcohol could be a powerful psychoactive drug with intoxicating effects on humanoids. The effects of polywater intoxication were similar to those of alcohol.
Due to its emboldening effects, alcohol was sometimes referred to as "liquid courage." (ENT: "Daedalus")
Vulcans didn't drink wine, and in fact were said to have been spared the dubious benefits of alcohol altogether. (ENT: "Breaking the Ice", "Home"; TOS: "The Conscience of the King")
Seemingly contrary to Spock's statement in The Conscience of the King, both Vulcan port and Vulcan brandy were mentioned to exist. Also, T'Pol, Ambassador Soval, Sakonna and Tuvok were all seen to consume alcohol, with T'Pol excusing it as a "small indulgence" due to the anniversary of her joining Enterprise and Sakonna claiming to respect "cultural idiosyncrasies". Spock himself did later drink Saurian brandy in "Requiem for Methuselah" and Tennessee whiskey in Star Trek V: The Final Frontier.
Alcohol could be used as a coolant or disinfectant. (TNG: "The High Ground", "Final Mission"; DS9: "Past Tense, Part I")
In 1957, Stron listed alcohol, frozen fishsticks and the constant threat of nuclear annihilation as the questionable things Humans had to offer. (ENT: "Carbon Creek")
In 2263 in the alternate reality, during a birthday party for Captain James T. Kirk, Jaylah consumed a large quantity of alcoholic beverages, having been told that it would take her "edge" off, but admitted to Montgomery Scott that this had not happened. (Star Trek Beyond)
When mixed with a theragen derivative, it blocked certain nerve impulses to the brain; such a mixture was used to treat the effects of prolonged exposure to interphase in 2268. (TOS: "The Tholian Web")
By the 24th century, alcohol was often replaced by synthehol, which carried all the properties of alcohol, but without the deleterious effects. Starfleet replicators were designed with optional programming to produce real alcohol though. (TNG: "Up The Long Ladder", "Relics")
Poteen was a traditional Irish alcohol that was quite strong, which continued to be brewed the traditional way by the Bringloidi of Bringloid V. The Klingons had an even stronger drink, chech'tluth. (TNG: "Up The Long Ladder")
It was impossible for Data to get drunk from alcohol. (TNG: "The Outrageous Okona")
In 2371, the high alcohol level in Fred Noonan's blood made it difficult for a vascular regenerator to heal his injuries. (VOY: "The 37's")
In 2374, a lifeform, having newly stolen Tom Paris' DNA, replicated five alcoholic beverages in USS Voyager's mess hall and became thoroughly intoxicated. (VOY: "Vis à Vis")
That year, Quark told Major Kira that people were willing to pay a lot for a glass of burning alcohol referring to flaming cocktails. (DS9: "Honor Among Thieves")