Older Than Print: One version of Tristan and Isolde has the eponymous lovers drinking a mixture from a vial, thinking it a lethal poison, only to discover instead that it was a love potion. Another version has Isolde's maid giving her a love potion and telling her to use it with her betrothed husband, King Mark. Isolde instead chooses to use it on her beloved Tristan, even though she knows the two of them can't be together. Still another version has them drink it accidentally, mistaking it for wine, or one where Isolde is already in love with Tristan and he alone drinks the potion meant for Ysolde (so she'd fall in love with Mark).
Isaac Asimov, inspired by the Gilbert and Sullivan operetta The Sorcerer, wrote a short story titled "The Up-to-date Sorcerer", in which the Professor's potion works because of Techno Babble instead of magic. It's a slightly more ethical potion than the usual sort, as it only works on people who aren't married. Predictably, it ends up making the pretty young girl fall for the wrong person, and all parties involved try to figure a way out of this mess. When they remember that the potion has no effect on married people, they realize that if the girl marries the guy the potion made her fall for, the potion will no longer work. They do, the potion wears off, they get the marriage annulled, and the girl goes back to dating the guy she was originally interested in.
In A Brother's Price there is a kind of drug that is commonly used on male prostitutes. What exactly it does is left unclear, though the implied "last longer" effect can not be the only one, it is probably a kind of powerful aphrodisiac, as a woman carrying it with her is seen as a sign she intends to rape a man.
John Collier's short story, "The Chaser," which inspired an episode of The Twilight Zone (1959), involves a Dogged Nice Guy who buys a love potion for just $1 to win over his unrequited love interest. The seller keeps talking about a $1000 "glove cleaner," hinting that, although he does not know if it cleans gloves, it does work as a Perfect Poison. He also indicates that using the love potion will turn his love interest into a Clingy Jealous Girl. Significantly more creepy than the episode, the entire story is told as the conversation between the buyer and the seller, strongly implying that the young man will at some point be back for the glove cleaner as the eponymous "chaser" to the love potion.
Implied, and played very darkly, in Chronicles of the Kencyrath. By the time we meet them, Torisen is avoiding Kallystine and waiting for their time-limited marriage contract to expire. From how Torisen mentions her, it's implied that a year or two back, their relationship was a Destructive Romance. It was an arranged marriage, and Kallystine was trying her hardest to seduce Torisen for political reasons. Torisen knew this perfectly well, and he came to resent and hate herů but it seems she did managed to seduce him for short periods of time anyways. It's implied that she was probably using magic do this.
His former consort had been adept at intoxicating the senses, but with an after-taste that had made him both loathe and mistrust his own passion. One of the Highborn subsequently thrown at him, a ridiculously young Ardeth girl, had seen enough to suggest that Kallystine had used potions to entrap him.
Some of Nanny Ogg's recipes have a very aphrodisiac-like effect, and people have been known to do amazing things after accidentally eating a plateful of something spiced up with her famous Chocolate Sauce with secret ingredients. The description strongly implies that she doesn't use magic, but natural aphrodisiacs. It can't break Granny Weatherwax's self-control, and another character is resistant because he eats a lot; implying that the effect is physical rather than magical.
The novel Mort has a brief mention of "Granny Weatherwax's Ramrub Invigoratore And Passion's Philtre". (This is a bit Early Installment Weirdness; later books would suggest that Granny sees this sort of thing as more Nanny's area, but at this point in the chronicles, Nanny hasn't been invented yet.)
In Dragon Bones, there is an offhand mention of a herbal aphrodisiac that the protagonist's mother had in her garden. It is used as a comparison when one of the characters is tortured, and notices that the torturer is a sadist who gets turned on by it. He compares the effect of his suffering on the torturer to that of said aphrodisiac on more normal people. Which raises the question how he, who was underage when he left home, knows about this.
In a short story from one of the Dragonlance collections, a kender (not Tas) has 'borrowed' a pouch from a mage he was travelling with. At the Inn of the Last Home, he finds while the pouch is perfect for his collection, it is full of a strange powder. He dumps it in the just-inspected ale-brewing equipment. The night the barrel of that particular brewing is served is very interesting at the inn, since the powder is of the love/lust-inducing-at-first-sight variety. Subverted at the end, when Otik Sandeth chooses not to use the doctored ale to gain the wife he longs for.
In Dragonvarld, certain people want Melisande to have a son, because that son will inherit powerful magic which they can point at the Big Bad. They therefore give Melisande and a man in her company a potion which makes them want each other (and also guarantees successful conception). It works, with neither of them knowing that a potion was involved (and therefore believing that they each betrayed their respective long-term partners).
The first book of The Dresden Files has Harry making a love potion at Bob's request (mostly because Bob wouldn't shut up about it), containing conventional (perfume, chocolate) and not-so-conventional (excerpts from a cheesy romance novel, a torn-up $50 bill in lieu of diamonds) ingredients. Despite (or perhaps because of) being called a 'love' potion, it's more of a really effective aphrodisiac than anything else. Susan accidentally drinks it instead of a teleport potion when she and Harry are cornered by a demon, and Hilarity Ensues.
Two of the Dresden short stories involve variations on the concept:
Last Call has a maenad dose Harry's favorite homebrew beer with a lust-and-violence potion in an attempt to start a riot at a Bulls game to remind people of Dionysus (and teach them "proper respect").
In Love Hurts, a Red Court vampire enchants a carnival haunted house ride to make the riders fall in love, hoping to spread true love, which is anathema to White Court vamps; she draws Harry and the cops' attention when people who shouldn't be in love (like siblings) fall victim and commit suicide. It's noted repeatedly in the series that any sort of mental tampering like this leads to insanity and frequently suicide, it just manifested in the victims Harry was investigating faster because they were siblings and thus had that extra taboo.
In Elvenbane, a complex multi-stage glamorie is used to by an elven Lady to get one of the half-elven to become completely devoted to her; he doesn't realize she's slowly casting him under a spell, and thinks he's falling in love. Luckily, unfinished glamories are fragile things; physical impacts, such as those from a former slave-lover, tend to disrupt them.
In The Eyes of Kid Midas, Kevin tries to use his newfound Reality Warper powers to woo his crush. Ironically, the attempt fails because she's secretly already in love with him, and all he ends up achieving is creeping her out.
One of Laurence Janifer's Gerald Knave, Survivor short stories involves a military project to douse the enemy country with aphrodisiacs so they'd be too busy screwing to put up a fight when invaded. Unfortunately, the chemicals keep leaking, causing the factory workers to get amorous when they're supposed to be working. The author included a comment on the dubious morality of this weapon, especially as the drugs only affect men.
Goosebumps: The book "Be Careful What You Wish For" has a non-romantic variation where a dorky girl helps an old woman who turns out to be a witch and gives her three wishes for her kindness. She wishes that the Alpha Bitch in her class who always bullies her will think that she's the greatest person who ever lived. They quickly become BFFs to everyone else's confusion, but she becomes so obsessed with her new best friend that she can't stop thinking about her and shows up to her house in the middle of the night.
In Harry Potter and the Half-Blood Prince, we learn that if not for a love potion, Big Bad Voldemort wouldn't even exist, since his mother, Merope, apparently used an extremely powerful one to make her crush, Tom Riddle (Voldemort's father) marry her. This is actually a subversion of the usual story, because the potion apparently did work perfectly. However, Dumbledore speculates she began to feel guilty after a while, and willingly stopped giving him the potion in the hope that he would have grown to really love her. Unfortunately, he didn't. Given how starved for love she was (having been raised in a highly dysfunctional family), Merope comes off rather sympathetically. Dumbledore speculates that Voldemort's conception being partly through artificially-produced love make him unable to feel any himself.
Love potions are banned at Hogwarts (although they are apparently legal in the wizarding world at large and are openly sold at stores that cater to students), not that it stopped Harry's fan girls from trying to slip him love potions in the forms of perfume, chocolate, drinks, and more, courtesy of Fred and George Weasley. One of those said slipped-love-potions caused Ron, not Harry, to fall in love with one of the fan girls.
It is noted in the books that love potions don't make the person taking them fall in love; instead, they create a powerful infatuation with the person creating the potion. Most of them are generally far weaker and more temporary than the one used by Merope; their main purpose appears to be Date Rape.
At one point in Half-Blood Prince, Harry compares love potions to Dark magic. Given that such potions can make a person act against their usual being (as proven with Tom Riddle and Ron in the same book), he's justified in being wary of them.
Oddly however one of the earliest mentions of love potions in the series is Mrs. Weasley telling Ginny and Hermione that she used one on her husband Arthur when they were in school. The book plays this off as innocent school-girl antics and then never references this fact again. This story is one of the primary foundations of Alternate Character Interpretationfor Molly.
This is discussed at some length in Doris Egan's Ivory series. A sorcerer can't make someone fall in love. Instead, he or she can create a spell that causes the victim to experience a very clinical checklist of symptoms of sexual attraction for the specified target; if the victim isn't suspicious, the result is effective about 80 percent of the time.
A whole industry of non-functional love spells can be found in Jonathan Strange & Mr Norrell. There was a spell to store emotions in amber, then when the amber melted the emotions spread to those nearby. Presumably, this could be used with love, although the actual examples were courage and fear for your and the other side's army respectively. It also featured a rather clever use of love spells Childermass buys a knowingly non-functional spell from Vinculus to use on a princess, bringing the wrath of the King down on Vinculus. Turns out he needn't have bothered.
In Kushiel's Mercy, the visiting general of a neighbouring empire gets his magician to make Sidonie fall in love with him using a spell that involves a very small tattoo between her shoulder blades. It also causes her to forget all about her passion for Imriel—though, as it turns out, it's not wholly effective. The spell is broken when Imriel cuts the tattoo from her skin. Needless to say, when she comes around, Sidonie is pissed. In this, the Unfortunate Implications of using a love potion—namely, that it's effectively rape—are fully spelled out.
In Naamah's Curse, one of the villains possesses a magical black diamond that entrances people who look at her, enabling her to become a queen. However, it's stated that this diamond does not compel false desire, or force anyone to be attracted to someone they wouldn't desire otherwise. Instead, it amplifies and enhances any slight attraction the wearer already inspires in people who encounter him/her. The wicked queen was a beautiful woman to begin with, and the diamond enhances her desirability so that anyone who would have been at least a little attracted to her without the diamond feels compelled to worship her like a goddess when she puts it on (which does still seem coercive, however...)
Labyrinths of Echo series by Max Frei is about a world with strong magic, so this one appeared too. It's not clean and reliable, though, and sometimes the victim is poisoned. The surest way to heal this is for the guilty to immediately, ahem, proceed with the seduction to the end. Fortunately, the limitation of the magic means that only very weak and safe variants are used, unless someone is lovesick enough to risk imprisonment just for making it. But the only guy who tasted it in the book managed to die at the first sip anyway — for nothing, because he was already quite charmed in the natural way. The victim, of course, was rather surprised by the new disposition upon revival... but willing to repeat the whole sequence if necessary and claiming he needs regular profilactics to stay alive. It ended up just very embarrassing, for everyone involved.
— Wait, when I managed to seduce you? Of course sometimes I talk in my sleep and all that, but it never occurred to me that even death has no power to shut me up!
Little Women: The sisters perform a play with a villain who purchases a love potion from a witch, along with poison to kill his romantic rival (probably to avoid that "power of true love" loophole). The witch, however, double-crosses him, stops the princess from drinking the potion, and slips the villain his own poison.
In Malediction Trilogy Catherine the witch (in her Back Story) is forced to prepare a love potion for her mysterious and highy dangerous employer. She has no choice but to fulfil the wish and while the potion works perfectly well, it all backfires horribly, leading to her being banned from the court and forced to live in the poorest slums of the city.
In the Night World book Spellbinder, Thea accidentally challenges Blaise's skills by saying she couldn't attract her soulmate. Blaise's response is to use a love charm. Not only does this not work, it still doesn't work when he is enchanted to hate Thea.
In On a Pale Horse, Zane is offered the use of a Lovestone by the Magician to seduce Luna (his daughter). Said stone compels instant desire and "is not something you can buy in knickknack shops". Despite being strongly attracted to Luna, and despite her stated willingness to honor her father's bargain (though she has no pleasure in it herself, nor interest in Zane), he declines the offer to use the stone.
In The Perilous Gard, this trope is subverted. Kate thinks Christopher has fallen in love with her sister Alicia. The queen of the fairies offers her a token that will supposedly make Christopher love her, which Kate declines because she would always know that he only loved her due to a potion. She finds out later that Christopher loves her, and the queen knew that, and the token was most likely nothing at all but a quiet form of revenge on the part of the queen.
Robert Bloch's story "Philtre Tip" concerns a man who is hopelessly in love with a married woman who wants nothing to do with him. He does some spell research and learns of a formula that will "transform ye beloved into a veritable bitche in heate". Even if she hadn't pulled a Poisoned Chalice Switcheroo on him, he really should've thought it through.
Tom Holt's JWW series, beginning with The Portable Door, centers around J.W. Wells' famous "love philtre", which always works - it knocks the drinker out for twenty minutes, and they fall in love with the first person of the opposite sex they see. There have to be something like five or six instances of this throughout the series, nearly always with horrific potential. As in all his books, Holt plays fast and loose with consistency, and a love philtre which "always" works somehow generally finds a way to wear off. At least until the very end of the third book, where the "hero" and "heroine" (if they can be described as such) are finally given such a heavy dose of the thing that they spend the rest of eternity making dovey-eyes at each other.
The aunts in Practical Magic cast love spells for any woman who asks. The only example given in detail is a cautionary one, as her new husband never gives her a moment's peace. However, the reader's viewpoint is almost exclusively on the woman. The effects on the man, or his ex-wife who he was faithful to before the spell and somewhat faithful to afterwards before being specifically hit with a spell to make him leave her, are hardly shown.
Schooled in Magic: They're available outside Whitehall, but banned inside. A love potion's effect can be permanent, and lessened only if redirected onto something else. It's stated any student caught with them will wish they were merely expelled. The ones outside Whitehall apparently don't really work, just give people confidence, and true love potions are much rarer. Later some are shown to be sold which only work if people drink them willingly, to insure a married couple stays in love to conceive a child.
Averted in Lois McMaster Bujold's The Spirit Ring. Fiametta tries to create a love ring, but her father explains that the spell only reveals true love, not compels it, and that magically induced true love is a paradox. The spell does work, just not on who Fiametta intended it for.
Corie makes some for a lovesick castle guard in Summers at Castle Auburn. The ethics of this are actually explored in the piece as she says her potion will only make the girl notice him, not love him. He has to do the work of getting her to fall for him. Corie could make standard love potions, but she doesn't want to practice "that kind of magic." A more standard love potion was involved in Corie's conception, which is acknowledged as a rape.
Sword of Truth makes mention of the morality issue; using a glamour spell, the series' equivalent of this, is seen by characters as tantamount to rape. Sorceresses who use it are either executed or expelled from the Palace of the Prophets (the Palace has a spell which slows down aging to about 10%, so there is little difference between the two for the exiles).
In the Vita Nuova, Dante admits that if his speech could fully communicate the worth of his lady, it would turn any of his listeners into lovers.
Piers Anthony's Xanth series includes magical "love springs." In this case, "love" is used as a euphemism - drinking from such a spring causes one to be compelled to mate with the first creature of the opposite sex that one sees, regardless of species. Love springs are supposedly responsible for the numerous Half Human Hybrids and Mix-and-Match Critters that exist in Xanth. What's worse, if you drink from it twice, you fall in love twice. Without losing your first love. Only time is effective.
The characters plan to employ a more traditional one (i.e. causing love instead of lust) to solve the magic induced Love Triangle between Prince Dolph, Nada, and Electra. Electra is cursed to love Dolph, and will die if he doesn't marry her. Dolph loves the sexy Nada instead, and Nada just considers him a friend but must marry him for political reasons. To fix this, Electra will take a potion to nullify the magic love she has for Dolph, marry him, divorce him the next day, and then Nada will take a love potion so she can marry Dolph. Instead, Electra's potion doesn't work because she truly does love Dolph, Dolph decides he loves her back during their one night of marriage, and Nada doesn't need to take the potion after all.