Noteworthy example in an episode of Angel Beats! where Naoi attempts to do this to Yuri with his Mind-Control Eyes. It is worth saying that in Angel Beats! happiness means death. Good thing it didn't work.
Benevolent example from Karin: Karin has an affinity for unhappy people, and when biting them (which injects blood instead of sucking it out, because she's an unusual kind of vampire), she induces a temporary state of wellbeing, overflowing energy and general happiness. From what we've seen, this effect can linger for well over a week. Fortunately, the rest of her family can perform Laser-Guided Amnesia, and will generally 'clean up' after her, so her 'victims' don't remember anything - they just wake up somewhere feeling really, really happy!
Her brother qualifies too, as while drinking blood, he also drinks stress, relaxing those he feeds on.
In the manga, while Karin's ability to devour unhappiness proved beneficial to some characters, its potential dark side was also shown in one incident when Karin wound up draining the unhappiness of a girl who had run away from home, gotten caught up in underage prostitution, but was about to run back home when she met Karin.
In Kino's Journey, Kino was born in a country where everyone is happy and content and loves their government... because they all receive a partial lobotomy in their early teens to eliminate discontent. The end of the Whole Episode Flashback has her escaping her knife-wielding parents' cheerful attempts to carry out her death sentence for non-compliance.
Happens to Luffy during the Little Garden arc of One Piece. Miss Goldenweek has "color traps" that induce a particular emotion in their victims. Luffy is recipient of two that replicate this trope, the first of which makes him laugh uncontrollably, and the second of which makes him sit down peacefully and enjoy some tea. While his friends are slowly getting turned into wax statues. The visible strain on his face as he tries to fight it, while still saying through gritted teeth "This...tea...is...DELICIOUS!" borders on terrifying.
Manaras "Click" revolves around a remote control and brain graft that can somehow control how turned on a certain person is.
Delirium, the Anthropomorphic Personification of madness in The Sandman, once encountered a little girl who paid her a compliment. "So I did something to her. Something so that she'll always be happy. Always be happy forever and ever and ever." Different from most examples of this trope, in that Delirium did this not for ulterior motives, but because of her Blue and Orange Morality born of madness.
In Action Comics #900, the finale of the "Black Ring" story arc, Lex Luthor merges with a powerful Energy Being from the Phantom Zone that grants him godlike power. As a demonstration of his new power, he sent a wave of pure bliss through all of creation. Of course, it didn't last. One of the conditions for keeping this new power was that it couldn't be used to do anything negative such as killing Superman and Luthor being Luthor couldn't accept that.
In Supergod, this is one of the creepiest aspects of Morrigan Lugus. In spite of being a huge bloated undead abomination, its presence biochemically forces human brains into a state of religious and sexual ecstasy, making the humans kneel before it in prayer and masturbation. Oh, and the same spores that have this effect on the brain also destroy the lungs - the first batches of scientists died.
The Flash villain Psycho-Pirate has the ability to control emotions, and he'll often use this Trope to sort out problematic people. When he winds up resurrecting a number of characters who died in the recent Crisis on Infinite Earths, he keeps them from being taken over by the trauma of their own deaths by saying, "Smile. Smile and be happy" which is an unusually benevolent version of his trope.
Celestia threatens to do this to Navarone in Diaries of a Madman, to put a stop to his increasingly self destructive attitude. She only stops when Nav tries to kill himself, rather than have his personality altered.
In Friendship Is Optimal, most humans are successfully uploaded into a simulated world that promises to "satisfy your values through friendship and ponies," and several epilogues show that this promise was followed-through on. Many of the humans have their lives manipulated with total disregard for ethics to coerce them into uploading. This caused around four hundred ponies to petition for death, death being the only possible means of escape, and Princess Celest-AI agreed that death would satisfy their values in only 86 cases.
In many incarnations of The Conversion Bureau, the ponification potion tends to do this. In mild cases, it makes the imbiber more likely to be happy. In more extreme (and creepy) cases, it makes the imbiber unable to feel any other emotion besides happiness.
The Conversion Bureau: The Other Side of the Spectrum is one of those extreme and creepy cases, taken Up to Eleven: not only is it nigh-impossible for them to feel emotions that aren't happiness, they also have no free will or ability to resist commands of native Equestrians, they have virtually no sense of self-preservation, they look brain-dead, and one character questions if they have any higher brain function. Which isn't even going into the horror of what happened to the TCB universe versions of the Mane 6 - their bodies have been taken over by sentient, twisted mockeries of the actual TCB!Mane Six, who are kept enslaved and tortured in their own minds while a fake pony happily lives out their life, ruins their relationships, and murders countless innocents.
Lines And Webs reveals that the Elements of Harmony have been tooled by Celestia to subconsciously do this to all ponies in Equestria as part of her Utopia Justifies the Means plan to end all violence and negative emotion in the world. The most prominent example is Twilight, who after figuring out the plan and trying to resist it, is blasted by the elements and MADE to accept.
In the Doctor Who fanfic, Time and Space, it is revealed in Chapter 6 the monster of the week is feeding on the negative emotions of the passengers of a cruise ship set adrift, leaving only the positive ones. The results are creepy.
Ella Enchanted, like the novel it's based on, has a part where Ella (who's under a supposed blessing that makes it impossible for her to disobey an order) is ordered to be happy about her curse and goes around being terrifyingly cheerful until someone gives her another order to snap her out of it.
In Star Trek V: The Final Frontier, the Vulcan antivillain Sybok uses his telepathic powers to remove people's emotional pain and replace it with euphoria, which causes them to be so thankful that they instantly become his devoted followers.
Slightly subverted in Whats So Bad About Feeling Good, the virus does this to people but it's purely a side effect; the seeming happiness infection is perfectly random in its ultimate source. Nevertheless, the Health Dept. considers this a threat and takes measures to confine it.
In the fourth Lethal Weapon film, Riggs and Murtaugh get information out of gangster Uncle Benny by dropping in during a dental appointment and turning up the nitrous oxide (laughing gas). Unfortunately the valve breaks and they all end up getting high with him.
Jack Frost from Rise of the Guardians has this power, albeit a less sinister version of it. Sometimes when his snow touches someone's face, it lingers for a moment, then you see that person happy and having a good time in the next scene.
In Mostly Harmless, Ford befriends a security robot by replacing its emotional control chip with a short piece of wire, thus forcing it to be happy whatever it did.
In Do Androids Dream of Electric Sheep? by Philip K. Dick, there's a home consumer product called a "mood organ" which allows you to change your mood, and most people use it to be happy all the time. Technically, they do that voluntarily, but really their lives are so miserable they don't have much choice. (Although there is one character who makes a point of setting aside a regular time, twice a month, to succumb to utter despair for a couple hours.)
In Larry Niven's Known Space series, an alien Pierson's Puppeteer uses a Tasp, which is a device which activates the pleasure center of the brain of anyone he points it at. You are happy when he uses it on you. It is very dangerous, because if used on you long enough, you become willing to be the slave of whoever is using it on you. Addiction is a real problem. By the second book tasps have apparently gotten more common in human society, despite being outlawed, and some people apparently do this to random people that look sad.
In the Foundation series by Isaac Asimov, there's a character called The Mule which due to a mutation is capable of controlling people emotions, in any way he want, and permanently if he wishes so. He uses this power to control his generals by creating loyalty in them; they know their loyalty is only due to his powers but they are unable to desire things otherwise.
The Bernard Werber novel The Ultimate Secret has a scientist get hooked on electrical happiness. Things degenerate after his death, and near the end his apprentice plans to implant the device to the captured protagonists to enslave them through addiction.
Ella from Ella Enchanted is under a curse that makes it impossible for her to disobey an order. She is once ordered to be happy about this curse. The results are downright creepy.
In The Dresden Files, any mental manipulation, even for good reasons, tends to cause catastrophic harm to the subject. As a result, painting a proverbial smiley on someone's soul will get you executed by the magical authorities.
In Summer Knight, the Summer Lady Aurora does this to Harry in an effort to convince him to abandon the task given to him by Queen Mab and the White Council to find the Knight's killer. Her motivations are altruistic; she sees Harry is deeply hurt by the events in the previous book, and believes that his interference in the events surrounding the Summer Knight's murder will get him killed, so she offers him a chance to find comfort and peace away from his own inner pain. It would also, of course, get Harry out of her hair so she could complete her plan to use the power of said Knight, whom she helped murder, to destroy the balance between the Faerie Courts and doom the world to a Neo-Ice Age.
In the short story "Love Hurts" from Side Jobs, a villain experimenting with redecorating people's minds to make them fall in love causes a number of mysterious suicides.
This is one way soma helps maintain the status quo in Brave New World. When the Savage starts to incite rebellion, the police respond not only with water pistols but with bursts of soma vapor and a prerecorded soothing voice. In fact, the riot began because the Savage disrupted the normally scheduled distribution of soma pills (a routine analogous to payday for the lower castes). Citizens are also engineered and conditioned from birth to love and accept their roles in society and to believe that their tier is the best tier to belong to. For example, Betas are conditioned to be glad they don't have to deal with all the responsibilities of Alphas, while still enjoying perks and advantages unavailable to Gammas and Deltas, such as nicer clothes.
Similarly in This Perfect Day by Ira Levin, the populace is given regular injections of happiness-inducing drugs.
Harry seems to be in a state of utter contentment while under the influence of Felix Felicis, a good luck potion. It's mentioned that too much at a time can cause giddiness and overconfidence.
The Imperius Curse works this way to the victim; it's a mind-control spell that seems to work by putting the victim in a blissful daze so they don't realize what they're being forced to do.
In the Mode series by Piers Anthony, Darius is in a position of leadership ("King of Laughter") in his home society, and his qualification is his ability to "multiply joy," making everyone feel the same joy that his wife does. No character ever seems to think that this practice is suspect because the happiness of the masses is "not true happiness," though Darius is bothered by the fact that it has adverse effects on the king's wife's capacity for joy—although even the wife is fully consenting to these adverse effects.
In the Uglies series brain alterations are performed on the pretties to make them cheerful and stupid. Almost all transformations in this series are accompanied by some form of brain alteration to make sure the subject accepts the change without question.
In Greg Egan's short story "Reasons to be Cheerful", the protagonist starts out afflicted with a brain tumor that makes him feel, not pleasure, but genuine happiness.
In Mary Andrew's "Fireborn Chronicles" the criminal elements of the universe are sent to a hive planet where they are addicted to a wonderful drug that can only be earned by working, but which the workers are completely content to work for in order to receive. In the second book this addiction accidentally happens to Ira's sister, and she comes to be much more accepting of her new life than he is.
In Insurgent, second book in the Divergent trilogy, we learn that one of the reasons members of the Amity faction stay so calm and happy is regular doses of a calming drug. Those who become extremely angry, as Tris does while staying there, will be given a higher dosage that temporarily blisses them out.
Unity did this by way of a collective consciousness in one of the Repairman novels. It could be resisted if the person infected is in the presence of a microwave, but Kate (who becomes infected) knows that prolonged exposure to the Unity will eventually cause her to enjoy her condition and do everything the collective tells her to do.
In Wheel of Time, during his final stand against the Dark One, Rand imagines a world without the Dark One and without evil. It turns out that is is equivalent to inflicting that trope to the whole world.
In Jack Williamson's novelette "With Folded Hands" anyone who expresses unhappiness with the overprotective nature of the robots in the story will be made happy, via the futuristic equivalent of a lobotomy.
In V (2009) they call it "bliss". The leader of the Vs, Anna, will stand in a special area and tell them calming things, and they become happy. Unfortunately, if Anna tries to do this to humans, she will almost bleed to death. In the second season finale, it is discovered that Ryan's Half-Human Hybrid daughter can bliss humans without dying.
In the Doctor Who episode "Gridlock", pharmacists on New Earth developed mood patches to achieve this effect, which The Doctor despises. Unfortunately for the inhabitants, a virus spread through a mood patch called "Bliss" and killed just about everyone on the surface.
On Sliders, the group ends up on an Earth where everyone has to wear a drug injection device on their arm that keeps them calm at all times. The promo for that episode was great: "The Sliders land on world where the government controls drugs...BY GETTING EVERYONE HOOKED ON THEM!"
In one episode of The Genie From Down Under the protagonist hands the Literal Genie a 27-page wish, highly-detailed to basically create her preferred life, complete with good things for all the people she cared about. Amongst them is the nanny/housemaid character, who is generally The Eeyore. The girl wishes for her to 'be happy'. And she IS happy, merrily singing a tune while dusting the mansion... by the end of the episode she's been carted off to a sanitarium for being ceaselessly, irrepressibly, and even ANNOYINGLY happy, all the time, no matter what. Good thing the show's genie happens to be a walking Reset Button with an Australian accent.
In one episode of Angel a woman who wants Angel to sire her tries to loosen him up with happy pills. Unfortunately she doesn't realise that Angelus tends to do what he wants and won't just go along with her wishes. He ends up squirting blood in her mouth and threatening her with torture.
Jasmine also does this to people just by being around her. It's part of the massive Glamour she projects.
One of Ally McBeal's clients was a businessman whom a non-malign brain condition had made perpetually happy. His son sued to force him into restorative surgery because he had also lost his business instinct and lost money for the company. He ultimately underwent the surgery voluntarily after his wife died and he couldn't grieve for her.
Earlier on in this same episode, the young lady who didn't want to become homogenized to look as good as everybody else was told by her mother to "have a cup of Instant Smile." It was pretty clear that "Instant Smile" was far more than just a brand name for hot chocolate.
An episode of Stargate Atlantis features a character who emits pheromones that work directly on the part of the brain controlling positive emotions. The result is a terrifyingly cheerful cast, including some rare smiles from the Perpetual Frowner and the Implacable Man.
In Kamen Rider Decade, one world has this done to much of the population. Basically, half the people are cheery and helpful Stepford Smilers due to basically being lobotomized into it, and the other half act that way for fear of having it done to them at the first sign of any rudeness or negativity, as is law on that world.
A Star Trek episode has the crew captured by the usual omnipotent aliens, who try to break their wills by telepathically forcing them through various humiliating actions. This includes making Spock laugh, which McCoy says will kill him if it goes on too long.
The episode "This Side of Paradise" sees an entire human colony and most of the crew of the Enterprise under the influence of a strange pollen, keeping them all in a perpetual state of bliss until some strong negative emotion overrides the effects.
A Deep Space Nine episode featuring Garak reveals that he became a victim of this. Originally, he had an implant in his head that would give him euphoric hormone rushes if he was ever subjected to torture (so that he could never be forced to reveal important secrets). Living in exile on the station, he is miserable and has little hope of ever returning home. So he built a controller that would let him turn on the euphoria device whenever he wanted... and, one day, he turned it on and never turned it off. Unfortunately, the device was neither intended nor designed for long-term use; Garak, having become completely dependent on the device to even feel normal, is left in near-crippling pain as it breaks down. The worst part, is that he is still dependent on it even as it slowly kills him: his mind doesn't clear from the euphoric effects until they actually turn it off to stop the damage it's doing to his nervous system.
In one episode of The Late Late Show, Craig Ferguson describes taking LSD as basically this trope.
House was dosed with anti-depressants by Wilson and became aware of the fact when he caught himself smiling when he tried to tell a patient why he believed she was going to die. He insisted on calling his state of mind "hazy" and claimed it could have impeded his faculties.
On Alphas, in the episode "A Short Time in Paradise", an Alpha has the power to do this, possibly by affecting a pleasure part of their brain, and uses it in establishing a cult. Two main characters, Cameron and Nina, fall for it. The side-effect is that people who experience it become sick and die.
The Path of Inspiration of the nation of Riedra from Eberron is ruled/led by extradimensionally-possessed psionics making the masses feel content about their respective roles in society, among other things.
In Feng Shui's 2056 juncture, the Bureau of Happiness and Productivity specializes in producing happiness drugs for the Buro. And that's the very least that these guys get up to.
One of the products of BHP is the Bonechills, a group of chemically and surgically 're-educated' individuals who are happy to commit unspeakable acts for their Buro masters. If a co-conspirator looks genuinely happy (as distinct from the Happiness Is Mandatory smile most people have) it's generally best to shoot him before he happily sets off his bomb-belt.
Paranoia. The Acute Paranoia supplement introduced the drug Gelgernine. The Computer often requires citizens to use it, which causes the lucky recipient to be blissfully happy until it wears off.
The Computer also uses it as an aerosol for riot control, with 30% projected casualties. And Gelgernine is the safest happiness drug in Paranoia.
Some GURPS sourcebooks have stuff in them which fits this trope. Such as rewiring a person's brain so that the mathematical center is connected to their pleasure center, and thus working out mathematical problems gives them pleasure.
In Dungeons & Dragons, the cursed "Helmet of Opposite Alignment" specifies that the wearer is completely satisfied with their new alignment, and views the prospect of undoing it as horrible. In other words, a Balor (one of the most powerful generic demons) will become a dedicated follower of law and goodness, and does qualify for paladinhood.
Orde, a Toa of psionics in BIONICLE, was assigned to work with the Zyglak and was supposed to "calm them down", which may have involved something like this. However, due to his own violent temper, Orde ends up inverting this trope and putting them into a permanent state of Unstoppable Rage.
In Judgment Rites, a Star Trek PC game, this happens to Spock thanks to an alien entity that has suppressed all emotions except joy. Paradoxically, Spock seems to be in agony about it.
The StarCraft series generally describes neural resocialization as having this effect on the convicts-turned-soldiers employed by certain Terran forces. "Resocialised" Terrans are said to be horrifying to normal people.
In Knights of the Old Republic II, it is possible to install a pacifist module on HK-47 (ordinarily an utterly sociopath who loves killing). He is so happy with his new, peaceful self that even a light-side protagonist is creeped out and removes it a minute later. He is then horrified by what he briefly became.
Mayor: You still look terrified. Okay, direct order. You like me. You trust me. You want to make me happy. End order. Mayor: Better now? Florence: Emotionally, much better. Intellectually, I think I'm screaming.
Sluggy Freelance: Riff shoots Bun-bun with a euphorant-tipped dart to keep him from killing Kiki. Bun-bun gleefully mangles him and Torg. Torg, previously dosed with the same drug, is thrilled about the lacerations.
In alternate dimension arc "4U-City", the entire population is kept under the effects of such a drug. With good reason, all of the citizens in the city survived a war and subsequent interdimensional invasions, many would be suffering from PTSD if not medicated. Even Riff can't handle it sometimes.
Para Ventura hacked AI by injecting "fond memories" of herself. As a result, she can explain it in details in their hearing range and remain loved. She considers this better than the guy who hacked one bot by reducing it to a mindless automaton.
The Charmer, from the Global Guardians PBEM Universe causes everyone around her to like her as if they were her best friend through the simple expedient of forcing them to be happy whenever she's around. The target thus associates happiness with the Charmer, to the point that they are incapable of being happy when she's not around anymore.
In the Homestar Runner cartoon "Happy Hallow-day", the extended absence of Halloween night, and thus the perpetual day it creates, forces Strong Sad out into the sunshine and denying him his daily dose of doom and gloom. At one point he complains that "something funny's happening to the sides of my mouth," and indeed it is; they're turning up. Later, wearing an expression of blessed contentment, he begs for someone to shoot him.
One of the more disturbing"if you think about it" aspects of The Monster Girl Encyclopedia is that the Demon Lord is basically doing a lust-based variant of this, to the extent of spreading her corruption not just over former flesh-eating monsters, but also over races that were originally on relatively amiable terms with humanity, such as elves, fairies, dwarves and mermaids.
The Superhappies in Three Worlds Collide want to do something like this to humans. In the normal ending, they do. It's treated as a tragedy.
Cavalier and Skybolt of the Whateley Universe apparently got this treatment to the point that they were absolute mindslaves to some of the badguys of Whateley Academy.
ThisCreepy Pasta starts off with an attempt to do this via genetic engineering. It...doesn't go well.
Seen in the Ren and Stimpy episode "Stimpy's Invention". Realizing that Ren is always unhappy, Stimpy gives him a Happy Helmet that makes him perpetually happy against his will. Once Ren breaks it off, he reveals that being able to getting pissed at Stimpy again makes him happy.
In Invader Zim, one of Zim's prisoners is a kid named Nick who has a thing stuck in his brain that makes him happy at all times. It's hilariously creepy.
In another episode, Shego and Kim both get tagged with chips that control emotions. They can do Happy, Sad, Angry, or Lovestruck (and spend a lot of time on the last two), as controlled by a remote that Ron mistakes for his Kimmunicator.
One episode of 101 Dalmatians had the three dalmatians, Spot the chicken, and their owners finding themselves in a medieval town that appears every 100 years. It's revealed that Cruella's ancestor ruled the town with an iron fist, and when no one stood up to oppose him, the town's witch (who also looks like the nanny's ancestor) puts a curse on a town that makes everyone and anyone who enters it mindlessly happy, making Cruella's ancestor all the more miserable in comparison. One by one, all the characters (except Spot, who was exempt from the curse because the witch had a pet chicken, and Cruella, who was her ancestor's descendent) fall under the spell, gaining mind control swirly eyes and becoming completely complacent. Spot manages to break them out of their spell by kissing them (also dispelling a fellow medieval puppy who thought Cruella's ancestor was a kind and loving man, who then vows to prevent Cruella's ancestor from making trouble, as he had planned to use Cruella as a replacement for the town so he may escape) and run out of the town before it disappears for the next 100 years.
The Transformers (Gen 1): "Changing Gears". The Autobot Gears, a perpetual grouch, is kidnapped and has a circuit stolen that controls the evil plan of the week - and turns him cheerful. After the rescue, the Autobots consider leaving it out, but Gears insists on reinstalling it.
In The Powerpuff Girls episode "Super Zeroes", Bubbles — who had reinvented herself as "Harmony Bunny" — tries this with what she dubs "Happy Stickers". They have no effect.
The Well Wizard in The Smurfs episode "Swapping Smurfs" turned Smurfs who went down to the bottom of the well into very happy zombies, all for the purpose of getting one of Papa Smurf's spellbooks so that the wizard could break the spell that kept him trapped in the well.
In The Venture Bros., Dr. Jonas Venture, as part of a state-of-the-art nuclear fallout shelter, included a system designed to occasionally dispense mood-altering drugs, considering there was a good chance any survivors of any nuclear war could conceivably end up traumatized. However, the AI assigned to run the complex disagreed, and, well, Dr. Entmann compares the conclusion she arrived at to a mother making her child smoke the entire pack of cigarettes she caught him smoking so he'd never smoke again (releasing a huge batch of the drugs via the ventilation system). It wound up being a total disaster, and Jonas didn't think twice in just vamoosing and bricking up the shelter. With a group of orphans left inside.
Happens in Jimmy Neutron, where an alien (who looks like and acts like a kindhearted granny, complete with cat looking minion) uses mass hypnosis to make the population of Retroville mindlessly happy (complete with unblinking eyes, stiff movements, and wide unbreakable smiles).
A few types of drugs can do this to a person for a short time. They include opioids, such as morphine and heroin, and drugs that affect the brain's dopamine system, such as cocaine and methamphetamine. After a while, however, the drugs start to become less and less effective at producing pleasure, because the brain has systems that will keep trying harder and harder to compensate for the drug's effects and return it to "normal". And once the "corrections" have kicked in, it takes a long time to get rid of them if you ever stop taking the drug. So instead of feeling normal when you're not on the drug and good when you are on the drug, you feel miserable when you're not on the drug while taking it only brings you up to "normal".
The hypomanic episodes that come part and parcel with cyclothymia (bipolar disorder's little sibling) can and often do feel the same way. It's not fun to feel simultaneously very refreshed and happy and totally petrified that it's only because you're within days or even hours of a cripplingly intense panic attack or a horrible bout with depression. (Full mania, while still dangerous and frequently regretted afterward, tends to totally overwhelm the brain's processes, so the energy and euphoria feel normal- which can be either better or worse, depending on how you look at it.)