Quirrel drank Unicorn blood while Voldemort was inhabiting his body, and he himself drank a potion containing the substance (mixed with Nagini's venom) as well. So does that mean Voldemort has this unspecified "half-life curse"?
Two part question: Does Voldemort have the unicorn-blood curse persisting throughout the series? and If he does, how does it affect him?
I would say drinking unicorn blood does nothing that would be observable to Voldemort.
Unicorn blood does 2 things:
" [...] 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
Voldemort: Yes. You see what I've become? See what I must do to survive? Live off another, a mere parasite. Unicorn blood can sustain me, but it cannot give me a body of my own. But there is something that can. Something that, conveniently enough, lies in your pocket!
We can see that it keeps him alive. But as for the curse I would say he was already cursed, so it would mean nothing and it would do nothing. And he was already living a half life. I mean the from the first quote I posted:
You have slain something pure and defenseless to save yourself, and you will have but a half-life, a cursed life, from the moment the blood touches your lips.
He had done extremely bad things and he was already dealing with that. He had made his worst enemy by trying to stop a prophecy. He was already living a half life as he had:
What could the unicorn blood have done to him? But perhaps make him live a quarter life? He would forever be a portion of a soul(as his other soul pieces were in various objects) and he had lost his original body.
We could also say that he is not human enough to even be hurt by unicorn blood. Because I would assume that Firenze was talking about humans being cursed. Voldemort had pieces of his soul missing and he was "borrowing a body" from Quirrel.
Also:
Canon does not say in any form. However, it is heavily implied that Voldemort's form at that point wouldn't even qualify as a 'half-life' without the aid of the blood.
While this could form an interesting twist for a fan fic, I would surmise that the ritual that brought Voldemort back into his full power in "Goblet of Fire" overrode any such curse. He shows no signs of being weakened in any manner at that point(beyond the changes to his appearance that make him a bit too distinctive to pass unnoticed, or even as human, really). More, the line "The Dark Lord will rise again with his servant's aid, greater and more terrible than ever he was," from Sybill Trelawney's second prophecy suggests that even if the 'curse' of drinking unicorn blood is present, it does not in any way leave him weaker than before failing to kill Harry Potter.
