Vitamin B12
Vitamin B12 shots. They treat deficiency; there is no good evidence that they add energy or burn fat when B12 is normal.
FDA-approved injection (cyanocobalamin) for B12 deficiency from malabsorption; methylcobalamin is sold compounded.
Used for
- B12 deficiency from pernicious anemia or poor absorption (the label use)
- Deficiency from metformin or a vegan diet
- Sold by wellness and weight-loss clinics for energy and fat loss (not shown to work)
How it works
B12 is needed to make red blood cells and to keep nerves healthy. Most of a shot is held in the body, so a deficiency is refilled with a few doses and then topped up monthly.
What the research shows
- A Cochrane review of 3 trials (153 people) found daily 1,000 mcg by mouth raised B12 about as well as injections, with low-quality evidence; oral costs less.
- A meta-analysis of 31 studies found people with diabetes on metformin had about twice the risk of B12 deficiency (risk ratio 2.09) and lower B12 levels, so yearly checks are advised.
- A meta-analysis of 16 trials (6,276 people without overt deficiency) found no effect of B12 on thinking skills or mood; only one trial measured fatigue, too few to judge.
- No trial has shown B12 injections cause weight loss or more energy in people whose B12 is normal.
Dosing
Dosing isn’t listed on the public site. In the app, each published option is shown with its source (a drug label, a clinical guideline, a trial or community reports) and can be turned into a protocol you review.
Work out the units to draw for your vial →Side effects
- Sore injection site
- Itching or rash
- Mild loose stools
- Rarely: allergic reaction, including anaphylaxis (label)
Cautions
- Check B12 (and folate) on bloodwork before starting: a shot does not fix a problem it was not given for.
- Do not take it intravenously: almost all is lost in the urine (label).
- Folic acid can hide the anemia of B12 deficiency while the nerve damage continues (label).
- Cobalt or B12 allergy rules it out; a rare hereditary eye disease (Leber’s) can worsen quickly (label).
- Multi-dose vials contain benzyl alcohol; severe kidney disease raises aluminum exposure from long-term shots (label).
- Shots raise blood B12 for days: mention them before a lab test.
Storage
Unmixed or unopened: Vial at room temperature (20–25 °C), protected from light.
From the Cyanocobalamin injection label.
One storage test
Room temperature, amber vials kept dark: above 90% of the starting amount for at least 181 days (the end of the test), with or without preservative.
Light was the risk: the authors say to keep the solution fully protected from light (clear syringes and glassware exposed it).
Methylcobalamin injections made in a compounding-supplier lab (PCCA), measured by UHPLC. Peer reviewed. Cyanocobalamin, the form on most labels, was not tested, and the test says nothing about germs in a vial punctured for weeks. A single test, not a use-by date. Ip 2019, Int J Pharm Compd (PMID 31085783)
More in Weight & metabolic
Reference only, not medical advice. Written for this app from the cited research. Doses marked community-reported are not from trials.