Hydroxocobalamin: vitamin B12 injections explained

Vitamin B12 is needed to make healthy red blood cells. When levels run low, the red cells that are produced do not carry oxygen well, and the result is B12 deficiency anaemia, with symptoms such as extreme tiredness or lack of energy. Hydroxocobalamin replaces the missing vitamin.

The NHS describes it as a manufactured version of vitamin B12. Common reasons for low B12 include pernicious anaemia, where the body cannot absorb the vitamin from food, and the use of metformin. Cobalin-H and Neo-Cytamen are the UK brand names listed.

The injection raises your B12 level directly, bypassing the gut, so that red blood cells can again be made properly. The NHS says it starts working straight away, but it may take a few days or weeks before your B12 levels and symptoms begin to improve.

Blood tests are used to monitor your B12 level and how well the treatment is working, and the dose is adjusted according to symptoms and results.

At the start of treatment you will usually have an injection a few times a week. Over time the gap grows, and the NHS says maintenance injections may be needed only every few months. It is given into a muscle by a nurse, or possibly a doctor.

Treatment can last a few months or sometimes years. For pernicious anaemia specifically, hydroxocobalamin is needed permanently. If you miss an appointment your B12 level can fall again and symptoms may worsen, so the advice is to rearrange it promptly rather than skip it.

• Pain, swelling or itching where the needle went in is usually mild and short lived.

• Attend your scheduled appointments, since the benefit depends on regular top-ups.

• Do not stop on your own, because levels would fall again and could cause harm.

Most adults and children can have hydroxocobalamin injections. Tell the person treating you if you have had an allergic reaction to it or to other medicines, if you have a cobalt allergy, if your potassium is low, or if you have an irregular or fast heartbeat.

Common effects listed by the NHS are pain, swelling or itching at the injection site, nausea or vomiting, diarrhoea, headaches, dizziness and hot flushes. These are usually mild.

Rare serious effects include palpitations, allergic skin reactions such as a rash or hives that can appear within 3 days (especially in people with cobalt allergy), and anaphylaxis. The NHS says to call 111 about palpitations or an allergic skin reaction.

• Call 999 for swelling of the lips, mouth, throat or tongue, breathing difficulty, a tight throat, blue, grey or pale skin, sudden confusion or drowsiness, fainting, or a raised, blistered or peeling rash.

• Suspected side effects can be reported through the MHRA Yellow Card scheme.

Hydroxocobalamin can be used in pregnancy, and treating deficiency properly matters for both parent and baby. It is compatible with breastfeeding, because B12 is a natural part of breast milk; a baby with its own B12 deficiency needs separate treatment. The NHS found no evidence that it affects fertility in either sex.

It is usually safe alongside other medicines, including painkillers. The NHS says there is not enough information to say that herbal remedies and supplements are safe with it, so tell your doctor or pharmacist about anything else you take.

Alcohol does not interfere with the injection, although the NHS notes heavy regular drinking can cause folate deficiency anaemia and recommends no more than 14 units a week. It generally does not affect driving or cycling, but if you feel dizzy, wait until you feel normal. You can eat and drink as usual.

Stopping the injections lets B12 fall further, so discuss any wish to stop, or any side effects that trouble you, with your doctor first.