The dosage of a vitamin B12-1000 injection is 1000 micrograms, according to Mayo Clinic. The injection is given either in the muscle or through an intravenous line.
The primary use for the injection is treating B12 deficiency, as stated by WebMD. The deficiency could be caused by lack of dietary intake or a disease process such as pernicious anemia or Imerslund-Grasbeck disease. In pernicious anemia, the body is unable to produce enough red blood cells because it is unable to use vitamin B12. The injection stimulates production and relieves symptoms. Imerslund-Grasbeck disease is an inherited condition causing chronic deficiency. When a person is unable to process dietary B12 in his diet, shots are required throughout his life.