The life force of the life pill is just in a weakened state and needs a lot of resources to recover. This is where the life essence serum comes in.
The life essence contains a lot of life energy. Unlike food, cells can make full of the energy in life essence directly. There is no need for digestion, a digestive system, or even a circulation system transport the life energy.
Life energy will be directly consumed by cells, be they plant or animal cells, on contact. So it has a very high usage efficiency. However, the process of creating life essence is very complicated and expensive.
Because the life energy had to be purified from corpses, only a small amount of it can be harvested from a corpse. However, the efficiency of harvesting is way higher if the serum is harvested from a living being.
