Zero can't drink the tablets because of two reasons. Zero(being a hunter) can't deal with the fact that he is a vampire and that he needs to drink the blood tablets so that he can live. Also the blood tablet isn't enough. Since he is slowly becoming a level E he is also slowly losing his capability to suppress his urge to drink real blood.
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vampire knight chapter 46 page 24
Only a Slayer's blood could cure Angel. Long story short, he had to drink Buffy's blood.
kaname " DRINKS" yuukis blood in "The Thorny Kiss"when he awakens the vampire in her when her fangs were destroying her from the inside
In different legions vampires only have to bite humans for them to become vamires. In vampire diaries You have to drink the blood of a vampire, die with the blood still in your system and feed on human blood for the transformation to be complete. In True Blood a vampire has to give you there blood, you die and are buried with your master until you raise as a vampire. Any of this helpful? Well these are just examples of how a human is transformed to a vampire. But in the real world unfortunately there are no vampires.
some vamps feed on animals, most in the show use blood bags and some drink straight from a human's vein