Ben Pace comments on Harry Potter and the Methods of Rationality discussion thread, part 20, chapter 90

Ben Pace 2 Jul 2013 7:29 UTC
8 points
In the first Canon, unicorn’s blood is silver, and that has a life-extension effect.

IIRC, Canon!Dumbledore says it is used as a last, terrible resort of a wretched life (or something).