Veritaserum

"Three drops of this and even You-Know-Who himself would spill out his darkest secrets. The use of it on a student is--regrettably--forbidden."

- Severus Snape threatening Harry Potter with Veritaserum.

Veritaserum is a powerful truth serum that is most commonly used in interrogation. The potion effectively forces the drinker to answer any questions put to them truthfully, though there are some methods of resistance. Use of the potion is strictly controlled by the Ministry of Magic.

Description and effects
Veritaserum is clear, colourless, and odourless and is almost indistinguishable from water. According to Severus Snape, the potion must mature for a full lunar phase, and is quite difficult to produce. It can be mixed with any drink, and three drops are a sufficient dose to make the drinker "spill out his innermost secrets". Thus, the potion forces the drinker to tell the complete truth to any question put to him/her.

Resistance and limitations
Despite being the most powerful truth serum in existence, it can still be resisted through different methods, including the taking of its antidote and Occlumency.

For the same reasons Muggles don't use polygraph tests, Veritaserum is no more reliable than its Muggle counterpart. Since some wizards and witches can resist its effects while others cannot, Veritaserum is "unfair and unreliable to use at a trial" and cannot be used as definite proof of guilt or innocence.

Another weakness is that the victim only states what they believe to be true, so the victim's sanity and perception of reality also factors in during interrogations. This is the main reason why Barty Crouch Jr. 's testimony was not credible, as he was clearly insane.

Known uses
Veritaserum was used on Barty Crouch Jr. in June of 1995, when Albus Dumbledore discovered that Crouch was disguised as the Defence Against the Dark Arts teacher, Alastor Moody. Severus Snape also threatened Harry Potter with it earlier that year because he suspected that Harry had been stealing supplies from his storeroom necessary to brew Polyjuice Potion. This was prior to the discovery that Barty Crouch Jr. was the one who stole the ingredients to disguise himself as Alastor Moody.

Dolores Umbridge attempted to use Veritaserum on Harry the following year, but to no effect. In actuality, Snape had presented her with a fake potion, and Harry only pretended to drink it, instead dumping it in one of her plants while she was occupied. Umbridge later asked for more Veritaserum after Harry broke into her office to contact Sirius Black, but Snape said it would take a month to make more. Instead, he suggested she use poisons on Harry if the situation were very grave. Snape also taunted her about using the entire bottle during one dosage rather than using the necessary three drops. As a result, Dolores suspended Snape and tried to use the Cruciatus Curse on Harry. However, Hermione Granger, who was also present, intervened and pretended to tell Umbridge the truth.

Though not used in the 1995–1996 school year, Horace Slughorn, the Potions master, taught his sixth year class how to make the potion for their N.E.W.T. examinations. Later, Harry suggested using it on Slughorn to collect a memory. Dumbledore rejected this idea since he knew that Slughorn could resist the potion with an antidote. Additionally, Dumbledore did not want to use force or coercion on the Potions master.

Lastly, Rita Skeeter used Veritaserum on Bathilda Bagshot while interviewing her for Albus Dumbledore's biography.

Etymology
The name comes from the latin veritas, meaning "truth", and the Latin serum which means "fluid" or "liquid".

Author's comments
J. K. Rowling has said that Veritaserum "works best upon the unsuspecting, the vulnerable and those insufficiently skilled (in one way or another) to protect themselves against it...just like every other kind of magic within the books, Veritaserum is not infallible". For this reason, she explained that even if Sirius Black had been given the opportunity to testify to his innocence under Veritaserum, the Wizengamot likely still would have found him guilty by claiming that Sirius was using trickery to be immune to it.

Behind the scenes

 * In the film version of Harry Potter and the Goblet of Fire, Snape says that Veritaserum would make even Voldemort spill his darkest secrets. This is most likely an exaggeration meant to intimidate Harry, as Occlumency can be used as a defence against it. However, in the book Snape merely states that it would make Harry spill his innermost secrets, which would almost certainly be true (though Harry's resistance against the Imperius Curse could indicate otherwise).
 * In Harry Potter and the Goblet of Fire, when Barty Crouch Jr. was being interrogated at the end of the year, Dumbledore shook three drops of Veritaserum into his mouth while he was unconscious. In the film version, Snape poured the entire contents of the bottle right into Barty's mouth while it was forced open in a struggle.
 * In the film version of Harry Potter and the Order of the Phoenix, Dolores Umbridge used Veritaserum on Cho Chang to force her to betray Dumbledore's Army by exposing the location of their meeting place, the Room of Requirement. Marietta Edgecombe, who betrayed the D.A. in the novels, was omitted from the film. Cho's unwilling betrayal was also the cause of her split with Harry Potter in the film, as Harry was unaware that Cho was under the influence of Veritaserum; in the novel, it was her continuing grief over Cedric Diggory, irrational jealousy of Hermione Granger, and defence of Marietta's betrayal.
 * Despite the potion's usage being heavily controlled by the Ministry, the usages over the series are unauthorised and/or illegal: Dumbledore did not acquire permission from the Ministry before using it on Crouch, Umbridge used it for interrogating students despite such action being forbidden, and Skeeter used it on Bagshot for an interview.

Appearances

 * Harry Potter and the Goblet of Fire
 * Harry Potter and the Goblet of Fire (film)
 * Harry Potter and the Order of the Phoenix
 * Harry Potter and the Order of the Phoenix (film)
 * Harry Potter and the Order of the Phoenix (video game)
 * Harry Potter and the Half-Blood Prince
 * Harry Potter and the Half-Blood Prince (film)
 * Harry Potter and the Deathly Hallows
 * The Queen's Handbag