"There is a room in the Department of Mysteries that is kept locked at all times. It contains a force that is at once more wonderful and more terrible than death, than human intelligence, than the forces of nature."
-- Dumbledore (OP37)
Amortentia is the most powerful love potion in the world. It is recognizable by its distinctive mother-of-pearl sheen and by the fact that its steam rises in characteristic spirals. The potion smells differently to different people according to what attracts them (HBP9).
References from the canon
- Love potions are banned at Hogwarts (GF27)
- Slughorn calls Amortentia the "most dangerous" potion because it does not create actual love, but an obsessive infatuation (HBP9).
- Harry and Hermione each perceived the scent in Slughorn's Potions Class (HBP9). Harry smelled treacle tart, a broomstick handle, and a flowery smell from the Burrow - possibly honeysuckle in the air as he watched Ginny flying on her broom (GF5); Hermione mentioned scents of parchment and freshly-mown grass; her third smell is Ron's hair (BLC).
- Merope Riddle tricked Tom Riddle into marrying her with a love potion, possibly Amortentia (HBP10). Even coming from a loveless marriage, baby Tom might have understood love if his mother had lived and cared for him (BLC)
- Romilda Vane tried to slip Harry a love potion inside some chocolate cauldrons, but Ron took it instead and fell in love with her for a short time until Slughorn gave him an antidote (HBP15, HBP18)
- Dumbledore told Harry that the locked room at the Department of Mysteries is where love is studied (OP37). At the center of the locked room is a fountain of Amortentia (TLC2)
"amor" L. love + "tempto" L. to try to influence or tamper with
Rowling explained the locked room at the Department of Mysteries where Amortentia is studied:
"What's in the Love Room. It's the place where they study what Love means. So that room, I believe, would have at its center, a kind of fountain or well containing a love potion, a very powerful love potion. You know that the first time they ever enter Slughorn's Potions class, and he starts talking about Amortentia, the Love Potion, and he says it's the most dangerous one in the room. That's what they would've found in the Love Room. So you would see wizards and witches taking it, they would study the effects. The room, of course, has to be locked." (TLC2)
While the Weasley Twins sold love potions, most of them were probably not as powerful as Amortentia.
Love potions are actually banned at Hogwarts, so why was Slughorn allowed to have a cauldron-full in his N.E.W.T. Potions class? It's possible that Dumbledore allowed it so Harry would hear Slughorn's lecture on the dangers of love potions before he showed him the memories about Merope Gaunt and the sad childhood of Tom Riddle.
Fan Theory: After viewing Snape's Worst Memory in the Pensieve, and feeling that his parents seemed incompatible, Harry wondered if somehow his father had forced his mother into marriage (OP29). While there was a long-running fan theory about the parallels between the Marauders with their "break all the rules" mentality and the Weasley Twins, who made and sold possibly illegal Love Potions, there is no hint that a love potion was ever involved in the James and Lily relationship. See also this fan discussion from 2005.
From the Web
"Amortentia" from Harry Potter Wiki