Where you receive the injection matters
When given by intramuscular injection, the dose bypasses the digestive tract and is absorbed reliably, which matters because dietary B12 absorption depends on stomach acid and a protein called intrinsic factor, both of which decline with age, medication and certain gut conditions
Some people also have a hard time absorbing vitamin B12 through digestion
Rarely a client will have itching, redness, or occasional bruising at the site of injection
Human studies have mainly focused on safety, how the body handles the peptide, and metabolic markers such as IGF-1 and glucose levels, but have not shown strong evidence of weight loss
Originally the source for intrinsic factor was virtually unprocessed normal gastric juice obtained from healthy volunteers