LD50 Oral (mouse): > 5,000 mg/kg ^F3733.

General toxicity

Vitamin B12 is generally non-toxic, even at higher doses. Mild, transient diarrhea, polycythemia vera, peripheral vascular thrombosis, itching, transitory exanthema, a feeling of swelling of entire body, pulmonary edema and congestive heart failure in early treatment stages, anaphylactic shock and death have been observed after vitamin B12 administration ^F3736.

Carcinogenesis and mutagenesis

Long term studies in animals examining the carcinogenic potential of any of the vitamin B12 formulations have not completed to date. There is no evidence from long-term use in patients with pernicious anemia that vitamin B12 has carcinogenic potential. Pernicious
anemia is known to be associated with an increased incidence of stomach carcinoma, however, this malignancy has been attributed to the underlying cause of pernicious anemia and has not been found to be related to treatment with vitamin B12 ^{FDA label}.

Use in pregnancy

No adverse effects have been reported with ingestion of normal daily requirements during pregnancy ^F3736.

A note on the use of the nasal spray in pregnancy

Although vitamin B12 is an essential vitamin and requirements are increased during pregnancy, it is currently unknown whether the nasal spray form can cause fetal harm when administered to a pregnant woman or can affect reproduction capacity. The nasal spray form should be given to a pregnant woman only if clearly needed, as it is considered a pregnancy category C drug in this form. Sufficient well-controlled studies have not been done to this date in pregnant women ^{FDA label}.

Use in lactation

Vitamin B12 has been found distributed into the milk of nursing women in concentrations similar to the maternal blood vitamin B12 concentrations. No adverse effects have been reported to date with intake of normal required doses during lactation ^F3736.