For a quick summary of common shot side effects see this guide: B12 shot side effects
The methionine component assists in breaking down fats in the liver and bloodstream, while choline helps metabolize fats and send them into the bloodstream to be used as energy [2]
If youre relying on getting all your B12 from fortified foods, make sure you get at least one serving at each meal containing at least 190% of the Daily Value listed on the nutrition facts label (based on the new labeling mandated to start January 1, 2020the target is 4.5 mcg three times a day)
This metabolite accumulates when B12 is functionally inadequate
If blood tests show clearly low levels (thresholds vary by lab, but often below roughly 200 pg/mL) or there are signs of anemia, a provider may recommend weekly injections for the first several weeks as a correction or "rescue" phase
Your dose needs may be different during pregnancy or while you are nursing