Parodied in the episode Ike's Wee-Wee, as quoted on the Main Page:
Cartman: "Drugs are bad because if you do drugs you're a hippie and hippies suck."
The above episode lampshades this as a chicken/egg Broken Aesop: Mr. Mackey's original intent is to prove that drugs make you a poor, depressed, homeless loser, yet, as he soon discovers, people turn to drugs because they are poor, depressed, homeless losers to begin with, and are driven to drugs to cope with said fact. When he tries to explain this to his rehabilitation counselor, she simply brainwashes him into once again believing that Drugs Are Bad, because, well, they just are, m'kay.
South Park has repeatedly mocked the way people exaggerate and even lie about the horrors of pot to try and keep kids from smoking it. Since marijuana isn't considered such a big deal nowadays, their main point about smoking marijuana is that when you're high you're not doing anything worthwhile - which is also a pretty good point.
"My Future Self 'n Me" deconstructs this, showing the lengths that parents will go to to Scare 'Em Straight, to the point of cutting off an actor's hand. It eventually reconstructs it with Randy giving Stan a perfectly sensible message against drug use. Word of God claims that this episode was inspired by a poster claiming that smoking marijuana supports terrorism. (For the record, the majority of the marijuana smoked in the United States is domestically grown.)
Several episodes of Captain Planet and the Planeteers, including a memorable one in which Linka became addicted to drugs slipped into a pastry, and her cousin died due to an overdose.
Depicted in a fairly believable fashion in a Super Hero and Science Fiction context in Batman Beyond without being Anvilicious. In the "The Winning Edge," a leading school sports team is using a super steroid based on the supervillain Bane's venom chemical in skin induction applications called "slappers." It makes the kids stronger, but at a price of excessive aggression and profound weakness in withdrawal as their dependency grows. Furthermore, when Batman goes to question the aged Bane about it, he finds him in a senior's home a complete vegetable totally dependent on Venom to stay alive; the natural result of using it for decades. (Sad Reality Subtext here: Robert "Jeep" Swenson, the actor who played Bane in Batman & Robin, died at 40 as a result of severe steroid abuse.)
G.I. Joe had an episode where the Joes team up with Freakin'' COBRA to take down a drug lord after one of the COBRA agent's sister gets hospitalized due to the drug lord's new product, "Spark". Cobra Commander only gets involved when the agent persuades him that, since drugs are big business, the drug lord is sure to have piles of cash on hand to steal. In a rare scene from a show heavy on the Bloodless Carnage, the drug lord gets dropped into a vat of pure Spark and dies from a horrific overdose. It also turns out that the drug lord's bags of "cash" were really bags of shredded newspaper.
Following the G.I. Joe example above, COPS' Big Bad, "Big Boss", uses his power to keep drugs out of Empire City. He helps the good guys stop a drug lord when his own nephew, The Dragon (the dumb Berserko), gets affected.
Specifically, an episode of COPS includes a new villain called Addictum who deals in a skin-absorbed drug called Crystal Twist. Big Boss and his gang help the cops capture him because Even Evil Has Standards.
"Alone Again" from Jem fits this trope. Laura, the newest Starlight Girl, is so depressed over her parents's deaths that she's easy prey for a drug daler. Pity about the Anvilicious Aesop, since the first five minutes describing Laura's self-hate and loneliness are an intenseTear Jerker.
The Simpsons kids' favorite cartoon, Itchy and Scratchy, spend a whole episode doing little more than standing on the screen and tepidly fighting. They end the episode with the non-sequitur "Kids, say no to drugs!" Bart and Lisa decide it was a pretty lifeless outing.
In Batman: The Animated Series, there is a slight subversion. In the episode, "Never Too Late", it's true that only the downsides to drug addiction are shown, but the episode focuses on the dealer himself and treats him with just as much sympathy and realism as every other villain they produce.
Completely and utterly ripped into by Sit Down, Shut Up. The teachers decide that they need a scapegoat problem to lecture about for Parents' Day, and decide to have an anti-drug conference sponsored by a prescription drug company. One of the teachers is declared the "drug czar" (for confiscating non-company drugs, including prescription drugs) and forced to quit drinking coffee, the negative effects of not taking prescription drugs are emphasized (including the principle going into a coma from various vital organs shutting down), and one of the teachers mishears "Math Lab" (he had previously been taking anti-ear-blockage medication) and instead builds a meth lab. Everyone seemingly gets sick from the meth being accidentally left among the dippng sauces, which is censored for being "kind of gross", and it turns out that nobody had taken drugs at all and they got sick from the food. For The Stinger, after it being said that they never did have a chance to show that drugs are bad, shows the baby who had several times been referenced as a "permanent consequence" of using drugs sitting in the duffel bag full of meth bags... andits tooth falls out.
In Capitol Critters the episode "Opie's Choice" dealt with a squirrel named Opie who was addicted to pep pills they caused him to stay awake at all times, have big baggy bloodshot eyes, and in order to get them he sells everything he owns, in that same episode Max the main character is captured by the drug dealers and force an entire bottle of the pills down his throat slipping him into a coma and almost dying as a result.
In Bravestarr's anti-drug episode "The Price", the kid actually does overdose and die. Shocking for a cartoon of that era, it's one of the best episodes of the series.
The episode goes even further by having his death by overdose come as a result of the batch his drugs came from being tainted, which was a second part to the warning that is Truth in Television about illegal drugs.
Of course, the message couldn't have been made clearer any time Tex-Hex's stooge Scuzz showed his face. Likely the most unpleasant villain on the show, he was a guy who smoked large, smelly cigars, and was always coughing badly because of them. Even the other villains were repulsed by him and his habit. (Of course, a kid's show like this is more than likely going to portray smoking as bad when they portray it at all.)
In an episode of Galaxy High Doyle takes "brainblasters" from a dealer to make him smarter and pass his classes, he soon becomes addicted to them and as a side effect he has big baggy eyes and zones out at the most inappropriate times, eventually he spends all his money and resorts to stealing from his friends to get more, eventually they get him to admit he has a problem after he goes to a planet that criminals hang out and returns their stuff, and he finds out that if he continued to use the stuff he could end up in prison.
One episode of A Pup Named Scooby-Doo had one of the suspects revealed to have a history with drugs. Every time the D-word was mentioned, the main characters (especially Scooby) expressed near-Pavlovian revulsion. Turns out the suspect in question was still involved in smuggling drugs, despite having given an Anvilicious claim that he'd quit that stuff.
An episode of The Littles appropriately entitled "Prescription for Disaster" played this straight in a surprisingly realistic manner for a Saturday morning cartoon.
In the Family Guy episode "The Thin White Line", Brian gets hooked on cocaine. While we don't see his withdrawal, we do see the terrible effects coke has on him - wild mood swings, paranoia, etc. Dogs, don't do drugs.
Subverted, in that Brian smokes weed and it isn't really shown as a bad thing. As do Peter, Lois, and the Evil Monkey. Even Meg has good connections.
And Peter/Carter sell Meg a bag. Then clock her and steal it back.
Inverted in the episode "420", where the characters sing a musical number extolling marijuana.
At which point a law is passed to legalize it, and everyone is completely stoned all the time with a few exceptions. Apparently in the world of Family Guy, there's no room for "responsible moderation."
In Family Guy???
Played straight in another episode where Brian overdoses on magic mushrooms and has a bad trip, complete with hallucinations, chills, etc.
Gleefully parodied in an episode of Futurama, where Fry and Leela use Zoidberg's "Miracle Cream" to give themselves superpowers, including super-strength and speed (but not the ability to control sea creatures). The powers are temporary, however, causing them to keep returning to the (apparently unique) tube of Miracle Cream. Shenanigans ensue when they run out. At the end of the episode, we are reminded in song that 'Winners don't use drugs!'
Used in Young Justice, where Superboy, a half-clone of Superman with weaker powers, is offered "Super Shields" which grant him full Kryptonian powers for an hour, at the cost of making him extremely violent, mindless and angry. They're also addictive, though whether that's the actual shield's fault or the power they give is ambiguous. Thankfully, Superboy realises how dangerous the addiction is to him (especially since it makes him dependent on Luthor), and comes clean of his own accord.
Done subtly in Transformers Prime, where Megatron frequently uses Dark Energon as a performance enhancing drug. Aside from the more esoteric and supernatural side effects that come from it being the blood of Unicron, there are familiar negative side effects, such as heightened aggression, loss of rationality, and psychological dependence. Granted, these realistic performance-enhancers are mostly subtle due to being overshadowed by the demonic possession vulnerability, the raising zombies, and the barring the user's soul from the afterlife.
Done more blatantly when Ratchet uses Synthetic Energon to similar (but more focused on) effect.