I would say drinking unicorn blood does nothing that would be observable to Voldemort.
Unicorn blood does 2 things:
Harry Potter wikia
" [...] 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
- Keeps you alive even if you are very close to death
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:
- Split his soul 6 times
- And he lost his body trying to kill a baby
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.
- It wasn't really him that drank it.
- And what is a "half-life"? Because I was assuming it meant he didn't have a full soul, but that already happened.