"Because… because you have lost the capacity for self-judgment. Now, alcohol does this, Wesley."
Intoxication was an abnormal physiological and psychological state in an organism in reaction to exposure to mind-altering or psychotropic substances, such as alcohol or recreational drugs of various kinds. Exposure to an intoxicating substance usually occurred via ingestion, inhalation, or dermal absorption of said substance. Intoxication manifested itself in many ways, including but not limited to slurred speech, loss of balance, loss of muscle control, irrational behavior, flushed skin, bloodshot eyes, erratic behavior, and loss of inhibition.
Scott and Tomar drunk on alcohol
Alcohol intoxication, also known as drunkenness or inebriation, exhibited all of the aforementioned symptoms; it occurred when a person had too much ethanol in their bloodstream. The level of excess alcohol led to physiological as well as psychological changes within an organism, which could range from mild to severe, depending on the amount of alcohol consumed and tolerance of the organism to the alcohol. The level of one's intoxication could be determined by measuring one's blood-alcohol level. (ENT: "Shuttlepod One") One who was extremely drunk was known by idiom to be "under the table". (TOS: "By Any Other Name"; DIS: "Saints of Imperfection")
People could be put in the brig for being intoxicated in a public place.
Zefram Cochrane was well known for his imagination and intoxication caused by alcohol. (ENT: "Regeneration"; Star Trek: First Contact)
In 2063, when the USS Enterprise-E traveled back in time to stop the Borg from preventing First Contact, Deanna Troi had to drink three shots of tequila to get Zefram Cochrane to admit his identity. She stated that she was only trying to blend in and William T. Riker agreed that she was, in fact, blended. (Star Trek: First Contact)
Polywater was another intoxicating substance. (TOS: "The Naked Time"; TNG: "The Naked Now")
In 2266, the USS Enterprise arrived at Psi 2000, where gravitational shifts associated with the disintegration of the planet resulted in the creation of large strings of water molecules known as "polywater". A member of a landing party from the ship returned back to the Enterprise carrying with himself the intoxication associated with the polywater and unknowingly passed it on to others on the ship. Spock became very emotional and he and James T. Kirk, overcome by emotions, even began hitting each other at one point. Before the ship could succumb to complete chaos and eventual destruction, Doctor McCoy was luckily able to find a cure. (TOS: "The Naked Time")
Captain Picard intoxicated with polywater
Nearly a century later, in 2364, the entire crew of the USS Enterprise-D also became intoxicated by polywater, once again resulting in everyone acting out of character and exhibiting severe mania with little to no inhibitions. Geordi La Forge, for example, became very emotional, crying that he wanted to have normal vision, while Lieutenant Tasha Yar seduced an equally intoxicated Data. Wesley Crusher sealed off main engineering as part of an experiment he wanted to conduct and declared himself "Acting Captain Wesley Crusher". Doctor Beverly Crusher and Captain Jean-Luc Picard were close to crossing the line themselves, but luckily, Doctor Crusher managed to find an antidote to combat the intoxication before the ship was destroyed. Captain Picard compared everyone's behavior to drunkenness. It turned out that the SS Tsiolkovsky, which the Enterprise-D had been sent to investigate, and its entire crew had essentially intoxicated themselves to death after exposure to polywater. (TNG: "The Naked Now")
In 2370, Odo and Quark arrested Kor after the latter was found intoxicated inside one of the Holosuites playing the Battle of Klach D'kel Brakt. Quark shut off the power and Odo arrested Kor and placed him in a cell to sleep it off. Koloth came by later to bail Kor out, but when he saw Kor was still drunk he told Odo to keep him and stormed off to the Replimat for lunch. Dax bails Kor out and the two of them leave to join Koloth at the replimat. (DS9: "Blood Oath")
In 2373, Jake Sisko untruthfully used drunkenness as an excuse for Nog and himself accusing Kai Winn Adami of burglary and the kidnapping of Elias Giger when the latter went missing. (DS9: "In the Cards")
Seven, drunk off her implants
In 2374, Steth, a shapeshifter with the ability to steal the DNA of any humanoid form, switched places with Tom Paris and posed as the real one on board the USS Voyager. Seven of Nine caught him with flushed cheeks and red eyes after he had replicated five alcoholic beverages in the mess hall alone. (VOY: "Vis à Vis")
In 2375, Seven became intoxicated after consuming only one glass of champagne at the christening of Voyager's quantum slipstream drive in engineering. After scanning her, The Doctor said, "Apparently, the Borg can't hold their liquor." (VOY: "Timeless")
Seven might have overcome this disability by 2399, as in PIC: "Stardust City Rag" she requests "bourbon, straight up".
In the same year, the USS Voyager was hosting Ambassador Tomin of the Kadi, a conservative race to whom formalities and proper etiquette, as well as dispassion and aloofness in every aspect of life, were highly valued virtues. Neelix, who was put in charge of Tomin during his time on board, made every effort to shield the ambassador from any kind of temptation to indulgences, but the ambassador was interested in anything but adhering to proper etiquette and dull diplomatic routines. On the contrary, he indulged in every vice he could imagine, one of which was consuming large amounts of synthehol. As a result, he drunkenly tumbled around the mess hall during a diplomatic event, bothering everyone; he came on to Seven, asking her to assimilate him, and he laughed at Tom Paris' jokes. This went on until he eventually passed out. Even though synthehol was not supposed to have the same effects on humanoids as real alcohol, in Tomin's case, the enzymes that broke down synthehol were not present in his bloodstream. Tom Paris joked that he might need "a cold shower" to sober up, but, in the end, Seven's nanoprobes were encoded to assimilate the synthehol molecules. (VOY: "Someone to Watch Over Me")
When, in 2377, The Doctor was forced to hide his program in Seven of Nine's Borg implants, Seven, controlled by The Doctor, began consuming large amounts of alcohol and acted erratic, losing inhibition and her otherwise stoic Borg apathy. Seven herself was not at all pleased with what The Doctor had done to her body, but The Doctor wanted to at least once experience the sensation of being intoxicated with alcohol, among other things. (VOY: "Body and Soul")
In one of the earliest series of notes concerning the development of Star Trek: Voyager (dated 30 July 1993), Executive Producer and series co-creator Jeri Taylor wrote that among the forthcoming series' main characters were to be "no drunks!" (A Vision of the Future - Star Trek: Voyager, p. 175)