Vitamin B12 injection

Vitamin B12 is needed to make new cells in the body such as red blood cells. A lack of vitamin B12 leads to anaemia, low energy, stomach problems (constipation, loss of appetite, weight loss), poor memory and nerve damage.

Most people get enough vitamin B12 from their diet. It is is found in meat, fish, eggs, and milk. It is generally not found in plant foods but many foods have added vitamin B12 such as breakfast cereals. A normal balanced diet usually contains enough vitamin B12. 

The most common cause of vitamin B12 deficiency is pernicious anaemia.  Some problems of the gut can also be a cause of vitamin B12 deficiency, but this is less uncommon, for example:

• surgery to remove parts of the bowel (the stomach or the end of the small intestine) 
• Crohn's disease 
• atrophic gastritis (where the lining of the stomach is thinned).

A deficiency of vitamin B12 can also occur with poor nutrition. Long term strict vegetarian or vegan diets (no animal products) are associated with a higher risk of vitamin B12 deficiency. This is especially important during pregnancy and breastfeeding when more vitamin B12 is needed.

The level of vitamin B12 in the body can be measured by a blood test. If you have low levels of vitamin B12 your doctor may prescribe hydroxocobalamin, which is given as an injection.  

• Hydroxocobalamin is given as an intramuscular injection, into the buttock muscle.
• The usual dose of hydroxocobalamin in people with pernicious anaemia is 1 milligram injected three times a week for two weeks, then once every two to three months.
• For people with gut disorders and older adults (over 50 years) who don't get enough vitamin B12 in their diet, hydroxocobalamin is given as twice yearly injections (every 6 months). This can be stopped when vitamin B12 levels have returned to normal and if the diet has improved. Women who are following a vegan diet may also need vitamin B12 injections if they are pregnant or breastfeeding. 

Like all medicines, hydroxocobalamin can cause side effects, although not everyone gets them. Often side effects improve as your body gets used to the new medicine.