Well look at how B12 affects the nervous system and what happens when theres not enough
(A wild edible tuber): A study on its ethnopharmacological potential and traditional use by the local people of Similipal Biosphere Reserve, India
The consistency across vial sizes reduces confusion when switching between protocols or vial batches
Having the shot directly in to the muscle allows the liquid vitamin to enter the blood stream quickly, bypassing the digestive system and the gastric acids and many other obstacles anything which is taken via the mouth has to go through to reach the small intestine, for re absorption
Telemedicine integration can further improve cost-effectiveness by reducing travel time and costs (Yeung et al., 2017)
If even one of them has a 5% impurity, you're not just introducing one unknown variable, but a cocktail of them that could interact with both of the primary peptides