The Connexus in Appleseed Ex Machina is basically a smartphone that you wear as a headset (it projects the images in front of your eyes). It becomes the must-have product in the Olympus consumer electronics market. It also has a nanotech chip in it that takes control of people's minds, turning them into what amounts to temporary zombies, when it receives a certain signal.
The villains of Blood+ had a variety of products including candy bars that could, under the right circumstances, turn consumers into giant freaky bat monsters.
Kemonozume's "health drink" made out of Flesh Eater claws.
Early Sailor Moon used this as a standard plot, with gyms, jewelery and radio shows as the product in question.
As part of his plan to take down Japan's society in Speed Grapher, Suitengu used the Tenozu megacorp to distribute products that contained a chemical that would lower people's inhibitions, making them more violent.
Essett, the Ancient Conspiracy in Weiss Kreuz, at one point marketed the "health drink" Freude to young girls as part of a Mad Science experiment; drinking it regularly eventually caused their skin to degenerate gruesomely.
The Cuddlesomes in the Big FinishDoctor Who audio adventure Cuddlesome: cute fluffy toys that will infect anyone who doesn't love their toys enough with an alien virus.
The soft drink Goruda in "The Golden Ones" strip in Doctor Who Magazine (actually a product of the Axons) which transforms children into aliens.
Beauline beauty cream in the Catwoman movie can transform regular users into Made of Iron, but if someone stops using it they look like a burn victim, and the heroine's best friend becomes ill enough to be hospitalized simply from using it regularly.
The "Regenerate" product seen in the adverts for the Resident Evil films, being made by the giant evil organization.
The 1989 Batman movie had the Joker lace beauty products with the ingredients for his trademark Smilex poison. The twist was that the contaminated products weren't poisonous on their own; they had to be mixed when the consumer used multiple products together, making it harder to find the cause of the poisoning.
And Batman Forever had the Riddler's "Box" devices which sapped people's intellect/thoughts and fed it to him; they didn't notice because they were so transfixed by the virtual reality imagery it beamed into their minds.
The 1995 Mighty Morphin Power Rangersmovie had Ivan Ooze creating a plaster-like stuff tainted with Ooze's blood that turned any person who touched it into a mindless zombie.
A variation in Idiocracy: Brawndo, The Thirst Mutilator, is harmful for plants, due to it being used to water farms, which results in the soil being salted by its electrolyte ingredient. Such usage is encouraged by the manufacturer, even going so far as to literally buy out the FDA to ensure the message gets through.
A further variation was used in Serenity via the Oaty Bar commercial which contained subliminal messages put there by the Alliance designed to trigger River's latent homicidal tendencies. (As far as anyone knows, the bars themselves are harmless.)
Averted by the lead-up viral marketing campaign for Cloverfield, which heavily featured a fictitious drink called "Slusho!", leading to online Wild Mass Guessing that the monster would be attracted to and devour its imbibers.
Basis of most of The Demon Headmaster books and their television adaptation, whether it's a mind-controlling computer game, a frightening pig-themed TV show or a DJ.
The Trippy Show in When the Tripods Came, a prequel to The Tripods trilogy.
The Stormbreaker computers from the Alex Rider novel Stormbreaker, which contain the smallpox virus.
In The Transformation from Marilyn Kaye's YA Replica series, teenagers' strange behavior turns out to be caused not by the candy fad or the hypnosis fad, but by subliminal messages in the television show everyone's watching.
Played for laughs in Harry Potter, when the Weasley twins test their products on unsuspecting students. These candies cause anything from mild illness to turning the person who eats it into a canary. Eventually, they develop Skiving Snackboxes, so that students can take one to get out of class, since they will cause you to puke or develop boils, etc.
In Kevin Brockmeier's The Brief History Of The Dead, it is suggested that the lethal virus threatening the world was spread by a new Coca-Cola formulation.
In Margaret Atwood's science fiction books Oryx And Crake and The Year of the Flood, the BlyssPluss pills are marketed as the ultimate sex aid: they act as contraceptives, prevent the transmission of STDs and enhance sensation. Unfortunately some of the pills also contain an artificially created hemorrhagic Ebola-like virus that wipes out almost the entire human race.
Downplayed and played for laughs, then subverted in The Laundry Series. Apparently Apple puts a low-level glamour on their products that makes people want to buy them. In The Fuller Memorandum Bob falls for it and buys an iPhone. It ends up saving his life after his friend installs anti-monster apps on it without permission.
Live Action TV
In Supernatural, the Leviathans take over - among many other things - companies that produce corn syrup, which is in practically every kind of fast food. They proceed to engineer the corn syrup so that it wipes out every other kind of monster, cures all major human diseases, and - oh wait - makes us docile enough to not notice we're being systematically killed and eaten on a worldwide scale. Dean's major concern, of course, is that he can't eat pie any more.
They didn't get it right first time though - their initial attempts turned people into ravenous, flesh-hungry monsters. And - to Dean's horror - an infected Turducken Slammer oozed grey goop when it was left for a while.
Doctor Who uses this trope to a ridiculous extreme. The new series alone has had phones that turn you into Cybermen, school dinners used to control children, television sets that steal your face, emotion patches that killed the entire government of New New York and 99% of New Earth's population, and a phone network of brainwashing.
Season four has weight loss treatments that animate your flesh and SatNavs/catalytic converters that poison you.
For the first one, the "may" part is actually accurate. On the original setting, the weight loss treatment actually removes that fat you didn't want, and turns it into a non-evil (and cute!) Adipose. But when it's ramped up to convert all your flesh...
The old series pioneered the trope with the Autons. While the image of the shop-window dummies is famous, anything made of plastic can be an Auton, from dolls to wheelie bins, and in one particularly hilarious instance, evil plastic chairs that eat◊ people◊.
A "Brent Smythe and Barry" sketch on Fast Forward involved Brent and Barry being asked to a market a product that consisted of fat, sugar and unidentified radioactive isotopes. They decided to sell it as a children's ice confectionery. Upon being told it eats through wood and plastic, they decided to make that a selling point: the only icy pole on a metal stick.
One episode of The Goodies has them attempting to dispose of a biological weapon for the U.S. Army. They sell it off as tomato soup to motorway cafes. It eventually ends up being used as petrol. And turns everyone into clowns.
Being a cyberpunk satire of consumer culture, Max Headroom was fond of this trope in general, starting with the blipverts in the Pilot Movie which could fuse the synapses of your brain.
While it never hit retail shelves, Vyvyan on The Young Ones hits it on the head, pointing out the inherent marketing advantage of selling Evil In A Coke Can:
Vyvyan: ... when the patient drinks it, he turns into an ax-wielding homicidal maniac. It's basically a cure, for not being an ax-wielding homicidal maniac. The potential market's enormous!
The Adam Adamant Lives! episode "The Sweet Smell Of Disaster" centers around a soap powder company distributing an addictive perfume in plastic carnations.
In S2:E9 ("Seasons Greedings") of Lois and Clark, a displaced toymaker comes up with a chemical formula which makes anyone who smells it act extremely greedy and childish. He invents a new toy (the Atomic Space Rat) to unleash the toxic substance on the public.
Every episode of Eerie Indiana: The Other Dimension featured a bad guy of the week who would open a store that featured this particular trope as part of their product or service. It invariably sold ridiculously well.
There also was an entire source book about Pentex and its subsidiaries which explored the multitude of themes possible. It also noted that the rather heavy-handed approach described above was once taken by a Pentex-owned computer hardware corporation. What do you get when you plunk a spirit of entropy and destruction into every piece of hardware you sell? Yup, a product that is entirely unreliable and won't be bought, thus entirely undermining the purpose of the whole thing. When the Pentex Board of Directors learned of this, they were... disappointed. The CEO's successor takes a more moderate approach, using it primarily to supply the other branches of Pentex with cheap computers - and of course selling a few outdated and mildly tainted models to schools.
The Pentex products that aren't loaded with Banes exist in two categories: ones that are otherwise geared at making the world a worse place (and thus contain more mundane evil than supernatural), or ones that aren't yet but will be as soon as they can come up with something suitably malignant. In the second category are things like the "End Run" mini-marts attached to Endron petrol stations, which will allow them to roll out whatever evil scheme they come up with so that it hits everywhere; in the first are things like King Breweries' beer, which only occasionally contains Banes but is always specifically designed to make your hangover a little bit worse than it would otherwise be. Then there's the occasional bit of memetic warfare, with companies like Avalon Toys (shoot werewolves like Action Bill does!) and Omni Television.
A majority of cyberpunk game adventures are about stopping an evil corporation from putting a nasty product onto the market - or testing it on unsuspecting street people.
The introductory story for Shadowrun 4th Edition subverts this. The Shadowrunner team is hired by a corp to put something nasty in a rival corp's soda in order to make it taste bad. The runners find out that the substance in question would have led to the mass poisoning of many of the orks and trolls it was supposed to be marketed to, and the culprit is their employer's human assistant, who it turns out is part of the human-supremacist hate group Humanis, who engineered this scheme to ruin the reps of both his boss and the group's fixer.
And of course, Scum Soda from Rampage: Total Destruction, which made people turn into giant monsters. The worst part is, even after the public found out nobody seemed to care anyways...
Proto-Cola of Defenders Of Dynatron City caused people to mutate. Strangely, it was both played straight and parodied at the same time: The Big Bad tried to use it to scare away the inhabitants of the city, but the people who used it viewed the mutations as beneficial.
Mineral powder in Eternal Sonata gives people the ability to use magic and heals illness before it turns them insane and kills them.
This is caused by the extreme physical dependency ADAM users suffer from. ADAM-granted physical changes are not stable, and decay in... unpleasant ways if not regularly topped up with fresh ADAM. The developers made the main character's hands become increasingly like those of a Splicer as the story progressed, implying that he's being affected too, although the really bad side effects take more time than the game lasts, and the worst gene cocktails for your sanity, the appearance modifying ones, aren't available for the player's use. Although, tthe good ending shows that he lives for several decades after the game ends anyway.
Metal Gear Solid 4: If you pay close attention to both the plot, and the various channels during the intro sequence, you'll notice lots of things with nanomachines...
Teleporter technology, the new killer app of United Aerospace Corporation in Doom 3. Yes, we do acknowledge that right now it tends to, well, open the gates of Hell, but our engineers are diligently working on the problem and we expect to have a marketable solution shortly!
MMO City of Heroes has at least a couple of easy examples from friendly neighborhood evil corporation Crey Industries. One is Crey Cola, a subtly addictive soft drink that would condition people to buy more and more of it as they drank. The other is the Crey OS, a computer operating systems which controls the minds of its users via subliminal messages, causing them, among other things, to want to buy more Crey-made products. That's sort of their business plan, to a large extent.
Then there's the actual drugs (Superadine especially) which make you super powerful... and irreversibly mutate you, and a great example you don't learn about till the late game. The Circle of Thorns are named for the 'spirit thorns' they use to make themselves more powerful. Only they don't actually make the user more powerful, they replace his soul with that of an ancient and powerful sorcerer. So it almost literally contains evil while being marketed as a power-up.
Almost everyone in Praetoria drinks Enriche instead of ordinary water. It makes you happy... and if not actually Brainwashed, less inclined to notice or care about the cracks in Emperor Cole's little Utopia.
Helen Narbon of Narbonic invented a self-cooling soft drink in a non-canon storyline. The problem (or rather, plan, since she's evil) was that it was STILL self-cooling inside the human body. 80% of the world's population died of hypothermia. Good thing it was non canon :p
When in El Goonish Shive, never accept a soda from Dr. Germahn. Odds are it'll shrink you but not your clothes. Granted, all he'll probably do is leer, so it's less "evil" and more "creepy", but still not a very pleasant experience.
Sluggy Freelance had the evil Hereti Corporation create the fast food chain House of Cheese. The food itself isn't harmful (at least not the stuff they give to the customers; a special pizza that instantly clogs arteries is reserved for their enemies), but the restaurant's logo is designed to trigger a homicidal response in the slightly unhinged fugitive experiment they're after. Once she sees a House of Cheese restaurant, she'll go insane and kill everyone inside, and Hereti Corp can use the series of fast food restaurant massacres to track her down.
Just to drive the trope home, every pizza is served with a small toy, that can be poison, or antidote. Explicitly labeled, for your convenience.
One fairly early Bruno the Bandit story arc involved a fast-food chain called Archio's, which was founded by a chaos demon. When a counterperson said "May I take your order?", if the customer replied "yes" then once they got the food home they turned into a mumbling shapeless blob. In a later arc the same chain sold shake-like concoctions made from bits of Archio's son Croatoan, which made habitual consumers morbidly obese by basically sitting around in your body forever and ever without being digested or excreted.
Renuyu in Batman The Animated Series allowed anyone to look young again... but if you stop using it, you suffer horrible pain and deformity. When an overdose was applied to a particularly recalcitrant actor, he became Clayface.
Your mileage may vary. Matt Hagen, the actor, was using the material to hide the injuries he sustained in an accident. It's up in the air how much of the his pain/deformity was caused by the original scars or related angst, and how much was directly caused by Renuyu
Power-8 from X-Men: Evolution was a delicious, refreshing sports drink - unless you happened to be a mutant, in which case it was poisonous.
In Squidbillies, Dan Halen Industires marketed Glug, a soda (actually moonshine) that makes people blind that so that the CEO can rob them. They also sold a body spray that causes hallucinations and melts human flesh.
Futurama had Slurm, a soda advertised with the slogan "It's highly addictive!"
The Slurm episode also parodies this with Soylent Cola, the taste of which "varies from person to person".
Chop Socky Chooks got jobs at Wasabi Burger to discover why they were so addictive. Turns out the special sauce was made from used body fat sucked out of Lipo Lounge customers. This made it an Anvilicious lesson on eating properly.
An episode of The Simpsons had a health drink distributed around town which accidentally contained peyote.
Then there's tomacco; the disgusting tasting but hideously addictive tomato-tobacco hybrid.
Any edible product endorsed by Krusty The Clown is likely to make you sick. It's also likely to contain ingredients that aren't technically food.
One episode of Archies Weird Mysteries involved an energy drink that when drank turned certain people (about one in every 10,000) into hulking monsters (like, literally Hulking). In a twist, the company had no intention of doing so, and immediately fixed the problem when Archie told them. However, they kept the whole fix secret to save their reputation, so the episode ends with them convincing Archie not to tell the public as hundreds of people would lose their jobs if the company went down.
The Oblongs. The kids get rich selling a sugar-laden energy drink everyone loves. It's obvious the drink is a horrifically unhealthy mess, but it turns out to be much, much worse. They used discarded 'morphine bottles' from the local hospital for their containers; the remnants of the morphine is what the people really wanted.
The Fairly OddParents had this with lemonade from Cosmo's stinky feet. The evil came around because Timmy temporarily valued cash more than his friend.
However, the problem was that the lemonade would randomly fulfill the drinkers' wishes (often without the wish needing to be stated, even), resulting in chaos.
G.I. Joe sees Cobra try this twice: Once with mind control music in "Cold Slither" and once with brainwashing personal products in "Let's Play Soldier"
The Totally Spies! episode "Passion Patties" has the Spies investigating a new super-addictive (and super-fattening) cookie being sold by the Happy Girls, which were the result of a mad scientist (and disgruntled ex-Happy Girl) putting an additive in the cookies.
Young Justice: Invasion: The Reach soft drink is designed to mutate human DNA over several generations, making humanity loyal to the Reach.
Tropical Fantasy Mountain Dew, only sold in Harlem (New York City) was thought by some paranoid blacks to contain infertility drugs dispensed by the KKK.
Similar rumors abound regarding far-more-widely available menthol cigarettes. There is a small grain of truth in this, though: while they don't outright make you infertile, they can make you impotent. Then again, so can any tobacco product.
Not that long ago, Hamas started a panic in Gaza over aphrodisiac chewing gum, supposedly sneaked into their territory by Mossad to 'destroy the morality of their youth'. Probably best described as a combination of paranoia and Values Dissonance.
With all the toy and food scares from products made in China, this is probably an example of Truth in Television. Only, without the mutant powers (yet).
Pop Rocks, a candy that fizzled when you put it in your mouth (the main reason being it had carbon dioxide in tiny bubbles) and would give off sparks if stomped on, got a number of urban legends that kids stomachs had exploded from consuming too much of the material (usually in combination with soda, causing a carbon dioxide cascade effect), the most popular of these being the actor who played Mikey in the Life cereal commercials. None of this proved to be true (and was thoroughly Jossed by Mythbusters), though a resurgence of the legends has recently developed, replacing the Pop Rocks with Mentos (also Jossed by Mythbusters; neither candy combined with soda will create enough gas to rupture your stomach, and in fact simply drinking the soda would decarbonize it before the cascade reaction with it and either the Pop Rocks or the Mentos could occur).
Urban Legends persistently surround McDonald's, usually that the meat in the hamburgers is not beef. Exactly what the rumor says it is varies from year to year; among the most surreal claims was that it was kangaroo meat, which would have had to be shipped halfway around the planet to be used in the US. Also, fun fact about that one: kangaroo filets are perfectly normal in Australia, meaning there would be nothing particularly evil about eating kangaroo meat anyway.
A similar urban legend claims that Kentucky Fried Chicken recently changed the decor and logos in its restaurants to show just the chain's initials instead of spelling out the word "chicken," because they are feeding the public genetically engineered chicken-creature-tumor-flesh grown in vats instead of actual chicken, and for reasons of legal liability they no longer claim it is chicken. Except on the menu, of course, right? Right.
Urban legends indicating the Powers that Be are dosing the food of males (colleges, the army) to lower their sex drive. 'Saltpeter' is the usual culprit.
This legend persists in spite of the fact that all the drill sergeants, training cadre, and officers all eat the same food as the trainees.
Another culprit is the Potassium Bromide, which was supposedly used in the in the British Army as well as in the Finnish Defense Forces. Spike Milligan mocked this legend in his war memoirs, claiming that the only way this could have possibly worked as planned was if they'd loaded the stuff into artillery shells and fired it at a British soldier from the waist down.
Also, veterinarians use Potassium Bromide as a sedative, so using it on troops heading into combat would have been counterproductive at best.
And don't forget about Tapeworm Diet Pills. Being infested with tapeworms will make you lose weight, so....
Jamaican Ginger, better known as "Jake". A patent medicine made to get around prohibition laws, it used a similar looking but better tasting chemical to the ginger solids it was supposed to contain, since the government test was done by boiling off the liquid and weighing the residue. The problem was said chemical was later found to be a neurotoxin that lead to numbness and partial paralysis of the limbs ("jake leg") with prolonged consumption.
A surprising number of people are convinced that the artificial sweetener aspartame, often used in diet soda, is extremely harmful, or going to control their minds, and that there is a massive conspiracy to cover this up.
Though a certain percentage of the population may develop headache and/or upset stomach upon ingestion due to an inability to properly metabolize phenylalanine (one of the chemicals into which aspartame breaks down), fueling the conspiracy theories further.
A study did prove that using too much increases cancer risk considerably, but bear in mind that the lab rats used were fed nothing but aspartame, so one dose in a cup of coffee per day shouldn't be an issue for anyone.
Coca-Cola used to contain a small amount of cocaine.
Its infamous "secret formula" will probably continue to generate conspiracy theories until the sun goes cold.