The Harry Potter books written by J.K. Rowling feature a large assortment of magical potions designed to do things like re-grow bones, force people to tell the truth, change a person's physical shape, or make someone fall in love. Some potions are only briefly mentioned, while others play a crucial role in the plot of the books, such as Polyjuice Potion, which is used by Harry, Ron, and Hermione in the their second year and again by Bartemius Crouch, Jr. in their fourth year. Harry himself struggles with Potions Class until sixth year, when Severus Snape is no longer the teacher.
Polyjuice Potion figures very prominently in the Harry Potter books. Polyjuice Potion allows the drinker to change into someone else physically for a period of one hour. Harry, Ron, and Hermione use it to spy on the Slytherin students, Barty Crouch uses it to impersonate Professor Moody, and Draco Malfoy uses it again in sixth year to conceal his henchmen while they keep watch for him. Polyjuice Potion is a difficult thing to make, requiring a long period of time and a hefty list of ingredients.
Another potion which is frequently featured is Veritaserum, a potion which forces the drinker to tell the truth when questioned. It is used by wizards during interrogations to ensure that they get truthful answers from the subject, and according to Snape, it is also very potent: a few drops go a long way. It is also among the more difficult potions to make, and requires the steady hand of a master. Other truth serums can be made, but may permanently damage the witch or wizard who is forced to drink them, so their use is frowned upon.
In Harry's second year, Mandrake Restorative Draft plays a prominent role. This potion can be used to restore people who have been Petrified, and also takes a long time to brew, thanks to the long growing time required for Mandrakes. Many other potions are designed for healing, such as Skelegro, which is designed to re-grow missing or broken bones. Healers apparently specialize in potions, among many other subjects, due to the large amounts of potions used on the job.
Love potions also are discussed in Harry Potter, especially in his sixth year, when characters begin taking a serious romantic interest in each other. In addition to ordinary love potions which range in potency, Harry is also introduced to Amortentia, the most powerful love potion known to man. The scent of Amortentia reflects the scent of someone's object of desire, and different witches and wizards describe it differently as a result.
Professor Snape is well established as a master of potions: in addition to difficult potions like Veritaserum, Snape is apparently very talented at crafting Wolfsbane potion. Wolfsbane potion treats werewolves, allowing them to turn into harmless wolves during the full moon, rather than full werewolves that could cause serious damage. Professor Lupin, a werewolf, takes advantage of the skill of Snape's to come teach at Hogwarts.
Perhaps one of the most intriguing potions in Harry Potter is Felix Felicitus, the lucky potion. This potion is described as a “pool of living gold,” which constantly shifts and leaps in the cauldron it is brewed in. A small amount of the potion will render the drinker totally lucky for a set period of time: every task undertaken will be successful, and the day will be more or less perfect. The potion is forbidden to people when they are participating in sports and examinations, because it would of course cause them to perform perfectly and answer every question correctly, thus constituting a form of cheating.