Verified purity matches the COA
Usually, a patient notices an increase in stamina within a couple of days of the first injection
B12 increases energy and metabolic rate while supporting weight loss, but it's most effective when combined with proper diet, exercise, and stress management rather than used as a standalone solution
As to the pain "going in" it may be that the needle caught a nerve or vein plus the fact that you were probably a little tense and nervous
Helms, R.A., Whitington, P.F., Mauer, E.C., et al., Enhanced lipid utilization in infants receiving oral L-carnitine during long term parenteral nutrition, J