Eternal Prohibition

Drugs Are Bad. So bad that even in the future, 20th-century drug laws remain unchanged. Nevertheless, alcohol and tobacco remain legal, as are 'stims'. Apparently, the citizens of The Future are more traditional than we realize.

This is most frequent in TV, presumably because producers are unwilling to risk controversy by including real drugs, but appears in other media as well.

Strangely, many future societies seem to have forgotten modern recreational chemistry, and have just one or two illicit drugs (e.g., Dust and Stims in Babylon 5), which you will never see a character actually using, but which is clearly bad.

Subtrope of Society Marches On. See Eternal Sexual Freedom and High Times Future for modern mores working in the opposite direction.

Examples:

Anime and Manga

 * Serial Experiments Lain plays this one: it's immediately obvious that 14-year-old Toru is doing wrong every time he's smoking or drinking at the Cyberia. There are stronger drugs, such as Accela, a type of "nanomachine amphetamine", is very obviously illegal, gives you instant Caffeine Bullet Time, and makes users homicidal and/or suicidal.

Comic Books

 * Inverted in Transmetropolitan. It seems like everyone does drugs all the time. It helps that they can fix any potential health effect. They're still illegal; it's just that almost nobody cares. They're still not good for you either, if certain descriptions of Spider's really bad days are to be taken at face value.
 * Averted in Paul Pope's 100% which is set in the near future, where marijuana cigarettes are legal.
 * Averted in Judge Dredd. In Mega-City, coffee and sugar are illegal, since they are addictive. Synthetics are used instead, but synthi-coffe was too good and became considered addictive, so it was outlawed. Hence, people drink synthi-synthi-coffe.

Film

 * In The 6th Day, tobacco is an illicit substance, and Arnie's character enjoys an illicit puff on one of his trademark cigars.
 * Likewise in Demolition Man. The first thing Human Popsicle Sly Stallone does on awakening is ask for a cigarette, only to be told it's illegal.
 * Happens literally in the 1930's sci-fi musical comedy Just Imagine, where Prohibition is still going strong in the far-flung future of 1980.

Literature

 * Averted in the titular Culture of The Culture novels. "Drug glands" are in-built in most Culture biological citizens, and other ways of shooting for the rainbow exist, and are completely legal.
 * Completely averted in Brave New World, where a hallucinogen called soma was specifically developed by the government as an ideal recreational drug and its use is encouraged. That's right, "Just Say Yes", foolish masses! A gramme is better than a damn.
 * In fact, they don't even have money anymore (at least we don't see it), people are just paid (by the government) in soma. When a couple of characters decide that maybe keeping everyone dosed and drugged all the time is bad, they try to disrupt one of the weekly distributions of soma. A riot breaks out when the workers realize what they are up to.
 * Often subverted, averted, or stomped upon in any Cyberpunk setting. And they usually do have more than one drug.
 * Shadowrun - drugs are mostly kept offscreen, because addictive simsense chips have (yeah, right...) taken their place.
 * Averted in The War Against the Chtorr series by David Gerrold, who goes to some trouble to portray a society that's changed both technology-wise and socially. Legal marijuana farms and over-the-counter recreational drugs are mentioned.
 * Used in a HP Lovecraft humour piece Old Bugs, which he wrote in 1919, which relates an encounter between a drunkard and a naive young man in a speakeasy for illegal whiskey-drinkers in 1950. (Lovecraft, who didn't drink, wrote it, however, to jokingly warn a friend, a.k.a. the "Old Bugs" of the title, as to what would happen to him if he kept on drinking.)
 * Several Philip K Dick stories have the characters smoking brand-name marijuana cigarettes.
 * The Stainless Steel Rat pops whatever pill he needs to get the job done, and although he's a criminal there's no mention of any of them being illegal.
 * On Nulapeiron, the setting for John Meaney's books Paradox, Context and Resolution, there doesn't seem to be any substance controls, and many different recreational chemicals are commercially available including many sophisticated materials that act upon the mind to induce dream states and the like. Marijuana and alcohol seem to be the most common, and no-one appears to smoke tobacco.
 * Humorously averted in the Doctor Who Eighth Doctor Adventures novel Alien Bodies: Sam Jones, in the near future and surrounded by aliens, focuses on a cigarette packet as a "normal" thing. Then she notices it says "CLOUD NINE -- The original cannabis cigarette". When she mentions the one time she got stoned, the future soldier the cigarettes belong to replies "One time? Are you sure you're human?"
 * Inverted in John Varley's Gaea Trilogy, in which a member of a NASA expedition to Saturn grumbles when he's cut off from his pipe tobacco. If the notion of NASA letting an astronaut contaminate a space vessel's limited air supply with secondhand smoke doesn't make this seem ridiculous, consider that the same spaceship's captain gripes about losing her own recreational supply of cocaine.
 * In Gabrielle Zevin's All The Things Ive Done, this is averted. Teens can drink all the alcohol they want, it's chocolate and other caffeine products that are banned.
 * Played straight, retroactively inverted, and averted hard in House of the Scorpion. The United States has cracked down on cocaine users and traffickers (at least within American borders) and Mexico retains bans similar to or slightly more strict than their pre-2009 laws (the book was written in 2002), but a country has arisen between the two that runs its entire economy on cocaine exports and brain-damaged clone slaves.
 * In EE Doc Smith's Lensman series, a good deal of the Galactic Patrol's efforts are spent thwarting illegal trade in "Thionite." When one Lensman goes undercover to infiltrate a Thionite trafficking organization, we discover that even plain old morphine is apparently still illegal.

Live Action TV

 * Battlestar Galactica: in early seasons the characters appear to live in the 1930s, drinking whiskey and smoking cigars. Partially subverted in the new series where 'Chamalla' is a legal hallucinogen sometimes used for religious purposes. And in one flashback President Roslin and Admiral Adama enjoy a an un-named substance strongly resembling Marijuana.

Fighter pilots are encouraged to take stims, which can lead to addiction if not carefully monitored, as exemplified by Kat.
 * Caprica averts this with the recent passing revelation that drugs have been legalized so as to quash any criminal market that may exist for them.
 * In contradiction of the trope's description, both those drugs are used by main characters in Babylon 5. As it turns out, there is very good reason that "Dust" is illegal--despite seemingly being Space Cocaine, it actually temporarily gives the user Psychic Powers, namely the power to Mind Rape someone (which G'Kar does to Londo after he gets his hands on some). As for stims, which aren't actually illegal, a major plot arc is Doctor Franklin's addiction and recovery.
 * Andromeda has obviously no problem with drinking. Though, nicotine seems to have become obsolete. The only drug left seems to be 'Flash' which is used as eye drops.
 * In the 1970-1 series UFO the characters smoke in computer rooms, medical areas, and closed environments like SHADO's underground headquarters, submarines and the Moonbase. Some scenes look like they've been filmed through a minor fog.
 * Near-subverted in the second season of War of the Worlds, set Twenty Minutes Into the Future: narcotics have been recently legalized, but this is presented as a symptom of the societal collapse that is in progress.

Tabletop Games

 * Legality varies greatly by habitat but drugs are very much a part of life in Eclipse Phase. The only "modern" drug featured is orbital hash but post-singularity narcotics range from bananas that decrease radiation damage to nanite-laced flowers that put you in a very trippy virtual reality.
 * Averted HARD in Over the Edge. Not only are drugs legal in Al Amarja, but there are some gloriously weird examples of Fantastic Drug too.

Web Comics

 * In The Lydian Option, "Janta Leaf" is portrayed as a mild drug being smuggled by the protaganist - humans view it as a minor offense, but the Tha'Latta punish it with permanent imprisonment.

Video Games

 * Somewhat justified the Crusader games, where the future world government is run a repressive Mega Corp that, while it doesn't care about worker safety, also probably wouldn't even allow things like cigarette breaks.
 * The Elder Scrolls has Moon Sugar, which is basically cocaine, as well as a drug called Skooma, made with refined moon sugar, which is basically crack.
 * In Mass Effect, a few drugs are mentioned. Red Sand and Hallex are both illegal narcotics of some kind (the former sounds like space cocaine and the latter like space ecstasy), and there's a substance called Minagen X3 encountered in a mission that makes your biotics unstable if you come in contact with it. Red Sand is related to minagen, they are both biotic inducing agents, red sand also melts your brain like minagen. Hallex isn't really illegal... what with it being Omega and all. You can also legally purchase Red Sand on Illum from a licensed provider.

Stims are mentioned several times as legal, and are common among military types. One mission has you getting some kind of stimulant for a human trade negotiator (who seems addicted). The product is legal, but he already used his monthly dose and isn't allowed any more. You can get him the stim or trick him by switching it for a tranquilizer.
 * Played with a bit in Eve Online. While plain old street narcotics and heavy-dose, skill-affecting "combat boosters" are nearly universally illegal, there exist versions of the latter that are universally legal; it's a bit like banning coffee, except for decaf.
 * And of course everything is legal in 0.0 space, where there is no police but that which the players muster themselves. And just like in the real world, drug manufacturing is quite profitable.
 * In the Wing Commander universe, Privateer allows players to smuggle two illegal drugs: "Brilliance" and "Ultimate". Getting caught with either means a shootout with police. You can, however, carry as much alcohol aboard your ship as it can hold without any paperwork, and not get in trouble.

Western Animation

 * Bender on Futurama smokes and drinks constantly. The alcohol is justified in that robots use it as fuel, and Bender will act "drunk" if he hasn't had a drink in a while. As for the cigars, "they make me look cool." The existence of other drugs is suggested. In "My Three Suns", for example, a junkie tries to buy crack from a vending machine (but the bottle catches on the spring), and in "Bender Should Not Be Allowed on Television", Farnsworth's and Hermes' kids are caught with one of Hermes' "cigars".

Bizarrely, cocaine seems to be legal, as it is openly sold in vending machines. However, marijuana seems to be still illegal, as Hermes makes frequent references to "flushing things", and "that's not a cigar...and it's not mine"; in the election episode, there's also a lobby for the legalization of hemp. The episode "Three Hundred Big Boys" has the same junkie say "No more cheap crack-houses for me!", and head for a huge building with a large sign reading "CRACK MANSION".
 * The Narm-tastic PSA The Drug Avengers plays this so hard that the main reason humans are kept out of The Federation is because people still use drugs on Earth.