That may still cause some confusion as people seem to be waiting until they die to try it the first time....Maybe something along the lines of when drunk it will infuse your body with the essence of life, allowing you to cheat death once when it comes.
Not sure if that makes it any more clear that you need to drink it before you die though....
This is a bit of threat necro but as of b20 this could still be improved. I got the blood of life and just assumed it was a passive bonus and would be removed from inventory when you died - didn't know you had to drink it.