No toxic or adverse effects have been associated with large intakes of vitamin B12 from food or supplements in healthy people.
Oral doses of 1 mg (1000 mcg) daily or 1 mg monthly by intramuscular (IM) injection have been used to treat ‘pernicious anemia’ (see Deficiency) without significant side effects. When high doses of vitamin B12 are given orally, only a small percentage can be absorbed, which may explain the low toxicity.
Because of the low toxicity of vitamin B12, no tolerable upper intake level (UL) has been set (27, 38).
Because of the potential for interactions, dietary supplements should not be taken with medication without first talking to an experienced healthcare provider.
Authored by Dr Peter Engel in 2010, reviewed and revised by Angelika Friedel on 29.06.2017