Vitamin B12 Cobalamin: Uses, Side Effects & Dosage Guide

Vitamin B12(another name of Vit b12 is cobalamin, Cbl) is water-soluble and is obtained from various sources like dairy products, red meat, and eggs. For absorption of vitamin B12 in the body, it needs another factor that is produced by the stomach and is known as Intrinsic Factor which is a type of protein called glycoprotein produced explicitly by the parietal cells of the stomach it makes a complex with vitamin B12 and then this complex is absorbed by terminal ileum. When absorbed, it acts like a cofactor for various enzymes that play a vital role in the process of synthesis of fatty acids, myelin, and DNA. If there is a deficiency of vitamin B12 in the body, it can lead to haematological and neurological symptoms. 

When there is an excess of vitamin B12, it leads to the storage of vitamin B12 in the liver And where there is a deficiency of vitamin B12 in the body (malabsorption, or lack of intrinsic Factor, dietary insufficiency) hepatic stores start to deplete. As a result deficiency of vitamin B12 occurs. Deficiency of vitamin B12 occurs primarily due to three main reasons: 

  1. Autoimmune: pernicious anaemia which is a condition in which there are antibodies against the intrinsic Factor. The antibodies against the intrinsic factor bind with the intrinsic Factor and inhibit it, which results in a deficiency of vitamin B12 as vitamin B12 can not be absorbed from GIT without intrinsic Factor. 
  2. Malabsorption: as the Intrinsic Factor is produced by the parietal cells of stomach patients having a history of gastric surgery are at the risk of developing deficiency of vitamin B12 because of bypassing the site at which production of intrinsic factor occurs. In regular patients, if there is any injury to terminal ileum like surgical resection of terminal ileum due to Crohn’s disease will decrease absorption of vitamin B12 and deficiency occurs. Some other causes that affect the small intestine and ultimately lead to vitamin B12 deficiency are inflammation or infection (Diphyllobothrium latum). 
  3. Dietary insufficiency: store of vitamin B12 in the liver is sufficient for almost three years if no dietary vitamin B12 is taken, but it eventually depletes in almost three years, and then deficiency will occur this is mostly seen in patients that are strictly vegans. Vitamin B12 is essential for maintaining Normal differentiation, proliferation & metabolic status of All the cells of the body. 

It is an essential coenzyme for two most critical enzymatic reactions: 

  1. Conversion of homocysteine to methionine 
  2. Conversion of methylmalonyl Coenzyme A(CoA) to the succinyl coenzyme A. 

The deficiency of Vit B12 in the body leads to accumulation of metabolites of these two reactions (homocysteine and methylmalonic acid) that eventually leads to the secretion of these metabolites into the plasma. Suppose the levels of these two metabolites are elevated in plasma. In that case, it strongly suggests the deficiency of Vit B12(cobalamin).there are multiple causes that produce an intracellular deficiency of cobalamin, which includes both acquired and inherited causes. Cobalamin deficiencies are found in strict vegetarians, and vegan and also a person with worm infestation ( tapeworm) or bacterial overgrowth also lead to cobalamin deficiency due to competition for dietary cobalamin. These patients are treated with supplementary cobalamin after the successful eradication of bacterial source of infection with antibiotics. However, patients who have gone through some GIT surgery like complete or partial gastrectomy OR ileum surgery(chronic inflammation) also develop cobalamin deficiency due to loss of intrinsic Factor which results in unable to cobalamin absorption from GIT or lack of ileal receptors respectively. Patients with cobalamin deficiency either due to acquired or inherited causes, are treated with intramuscular injections of cobalamin according to pharmacological doses. Use of ethanol is another factor of intracellular deficiency of cobalamin.


Use of cobalamin is indicated in the following conditions:

  • Vitamin B12 deficiency (the condition in which blood levels of Vitamin B12 is are low)
  • Imerslund-Grasbeck disease (a rare inherited condition marked by vitamin B12 deficiency) 
  • Age-related macular diseases
  • Canker sores
  • Postherpetic neuralgia (nerve pain caused by shingles)
  • Alzheimer’s disease
  • Angioplasty
  • Atherosclerosis
  • Eczema (atopic dermatitis)
  • Breast Cancer
  • Colon cancer
  • Rectal cancer
  • Lung cancer
  • Pancreatic cancer
  • Diabetic neuropathy
  • Peripheral neuropathy
  • Depression
  • Diarrhoea
  • Fatigue
  • Inflammation of the liver caused by hepatitis C
  • Hypertriglyceridemia
  • Infant development
  • Infection of airways
  • Psoriasis
  • Tinnitus
  • Venous thromboembolism
  • Chronic fatigue syndrome
  • Lyme disease
  • Memory problems
  • Multiple sclerosis
  • Chronic alcoholics
  • Atrophic gastritis
  • Celiac disease
  • Crohn’s disease
  • Pernicious anaemia
  • Ageing
  • Heart disease
  • Diabetes 
  • Vegetarians or vegans
  • Chronic pancreatitis
  • Gastric bypass surgery
  • Intestinal bacterial overgrowth
  • Intestinal fish tapeworm
  • Cyanide poisoning
  • Hyperhomocysteinemia 
  • Medications


Cobalamin is contraindicated in the following conditions:

  • low amount of potassium in the blood
  • Leber’s hereditary optic atrophy
  • Post-surgical stunt replacement
  • inflammation of the stomach called atrophic gastritis
  • history of complete removal of the stomach


  • Cobalamin And Derivatives
  • Cobalt
  • Vitamin B

Side effects

 The common side effects of cobalamin use are:

  • injection site reactions (pain, redness, swelling, irritation)
  • Megaloblastic anaemia
  • Polycythemia vera
  • diarrhoea
  • nausea
  • Gastric upset
  • itching
  • Rash
  • headache
  • dizziness
  • weakness
  • numbness or tingling
  • fever


Cobalt should not be given to patients with a history of cobalt allergy or diagnosed case of Leber’s disease ( use of cobalt in Leber’s disease can lead to damage to optic nerve possibly blindness in some patients). Cobalamin should be given with precautions in patients of heart disease, diabetics, bleeding or clotting disorders, iron or folic acid deficiencies, gout, low level of potassium in the blood, intestinal disorders like ulcerative colitis And in pregnant or breastfeeding mothers.

Cobalamin has drug interactions with the following drugs

  • Chloramphenicol

High-risk groups

High-risk groups for cobalamin use are:

  • Diabetics
  • Heart patients
  • Pregnant or breastfeeding mothers
  • Patients with intestinal disorders
  • Bleeding or clotting disorders
  • Allergic to cobalt
  • Patients with Leber’s disease
  • Gout
  • Patients with iron or folic acid deficiencies