Pros: Necessary for some who have had gastric bypass.
Cons: b-12 is a thick fluid so the injection stings a bit.
Vitamin b-12 is only absorbed in the stomach due to the intrinsic factor. About 5 years ago I had a gastric bypass surgery. It is not uncommon for people who have had this surgery to require supplemental b-12 in the form of an injection. There are online pharmacies who sell the injectable form--but you have to give yourself a shot. The best way to get b-12 is ask your doctor. They can perform a blood test to see if you need it.