This equalizes the pressure and makes it much easier to draw the liquid out accurately without fighting a vacuum
If you develop severe allergic reactions such as difficulty breathing, facial swelling, or widespread rash after a B12 injection, call 999 or go to A&E immediately, as these may indicate anaphylaxis, though this is extremely rare
Anyone with significant medical conditions, anyone pregnant or breastfeeding, and anyone on multiple medications needs a careful review first not because problems are expected, but because limited human data means we don't assume
Hormone Research, 53(6), 274278
Vitamin B12 injections are the most common way to prevent or treat a deficiency.