after taking vitamin b12 injection what happens How Shots Improve Energy, Mood & Metabolism Vitamin B12 Injections: Hot Shots?
Description
They aren't supplying B12 for any medical condition, so they don't have to worry about what they sell going off

A few reasons: Energy support
Improves Sleep: Many users report improved sleep quality, likely due to the increased endorphin levels that also help regulate the sleep cycle
Vitamin B12 also helps prevent megaloblastic anemia, a blood condition that makes people tired and weak.
