Hello everyone, Unicorns are universally revered as sacred creatures, so we need to kill them. Not really, but in case your players happen to do so, here's a handy item that lists exactly what happens following the ingestion of such blood.
If you do play with alignment in your game, an effect that you can add is the following: 'When you drink a unicorn's blood, your alignment changes from good to neutral, or from neutral to evil. If you are already evil, you regain half as many hit points upon drinking it.'
You can also make the curse far more nefarious, but I'll leave that up to you.
(Dungeons and Dragons 5e Item)