Unicorn blood

"...it is a monstrous thing, to slay a unicorn. Only one who has nothing to lose, and everything to gain, would commit such a crime. The blood of a unicorn will keep you alive, even if you are an inch from death, but at a terrible price. You have slain something pure and defenceless to save yourself, and you will have but a half-life, a cursed life, from the moment the blood touches your lips."

- Firenze explains to Harry Potter why the slaying of a unicorn is a crime.

The blood of a unicorn can be drank in order to keep a person alive. However, the act of slaying a unicorn will cause the drinker to suffer a cursed life.

History
Lord Voldemort used unicorn blood while attempting to regain his former power.

Appearances

 * Harry Potter and the Philosopher's Stone
 * Harry Potter and the Philosopher's Stone (film)