injection of vitamin b12 side effects and Safety Vitamin B12 Injection: Uses, Benefits,
Description
Randomized intervention studies with one-time injection of 400 g hydroxycobalamin are reported to improve the metabolic pattern and gross motor development compared with infants receiving placebo (Torsvik et al., 2013, 2015)

If you're older, you may also want to have your B12 level tested to gain the full picture of the dosage you need

The vitamin is delivered straight into your muscle, allowing it to be absorbed directly into your bloodstream

doi:10.1016/0952-3278(95)90118-3 Li C, Li J, Jiang F, et al

By blocking NNMT , 5-Amino-1MQ: At the enzyme level it binds within NNMTs substrate pocket with high selectivity
