(covers information from several alternate timelines)
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.
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 Scotty 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")