Muggles' Guide to Harry Potter/Magic/Amortentia

Overview
Amortentia is an extremely powerful love potion.

Extended Description
The first, and as it turns out, only Love Potion mentioned by name, Amortentia is introduced by Professor Slughorn in Harry's first Potions class in year 6. Discussing the characteristics of the potion, Hermione says that it is mis-named; it does not actually produce love, only infatuation, possibly obsession.

Analysis
Love potions have been a staple of Muggle belief in magic, as long as we have had the concept of love, probably. The need to have someone love you back, and the hope that there would be some magic technique to make that happen, is all too human. Writing a series of books about magic, then, almost requires that love potions be mentioned, and a series such as this one, where the characters are maturing to the stage where love occurs, probably need more than a mention.

In this series, then, we see mention of Amortentia, and we also see that love potions, probably including Amortentia, take a small role in the series. It is in Harry Potter and the Goblet of Fire, the fourth book in the series, that we first hear of them, in a story by Rita Skeeter in which she suggests Hermione is using love potions to keep both Harry and Viktor Krum "on a string." However, it is not until the sixth book, Harry Potter and the Half-Blood Prince, that our protagonists are really old enough to care about romance, and it is possibly because of this that this is also the first book where they are used. An important distinction is drawn immediately by Hermione, who points out that so-called love potions do not create love, but only infatuation; presumably this is why their use is so limited.

In the series, then, we first see Amortentia, described as the strongest of the love potions, in Harry's first Potions class. We then hear that Merope Gaunt had probably used a love potion on Tom Riddle to get him to marry her, and had given birth to Tom Marvolo Riddle as a result. There is some abstract discussion of love potions in the run-up to the Slug Club Christmas party, with Hermione warning Harry that several girls, notably Romilda Vane, had apparently purchased love potions from Weasleys' Wizard Wheezes. Ron samples some of the Chocolate Cauldrons that Romilda had given Harry, and becomes infatuated with her, proving that she had spiked them with love potion. Except for the first instance, in which the potion is explicitly named, we do not know whether any of the other instances are actually Amortentia, though we do know that Hermione identifying it as the "strongest" implies that there are at least a few other love potions available.

We believe that love potions were not introduced until the sixth book because of the age of the protagonists; the Trio would not have wanted the specified effects before they reached that age. Because of the limited interpersonal interaction in the final book, there was no need to include love potions. So their use seems to be entirely restricted to the sixth book of the series.