About hydroxocobalamin

Hydroxocobalamin is a manufactured version of the vitamin B12. It is used to treat and prevent vitamin B12 deficiency anaemia (when you have low levels of this vitamin in the body).

Hydroxocobalamin is only available on prescription.

It's given as an injection. This will usually be at your GP surgery but can sometimes be given to you in hospital.

Key facts

  • Hydroxocabalamin starts to work straight away. However, it may take a few days or weeks before your symptoms start to improve and you feel better.
  • At first, you may need to have the injection a few times a week to boost your levels of vitamin B12.
  • Some common side effects are feeling or being sick and diarrhoea.
  • It's safe to take for a long time. Some people may need to take hydroxocobalamin for the rest of their lives.

Who can and can't take hydroxocobalamin

Most adults and children can have hydroxocobalamin injections.

It's not suitable for everyone.

To make sure it's safe for you, tell your doctor before starting hydroxocobalamin if you:

  • have had an allergic reaction to hydroxocobalamin or any other medicines in the past
  • have been told you have low levels of potassium
  • have an irregular or fast heartbeat

Having your injection

A nurse, or possibly a doctor, will usually give you your hydroxocobalamin injection. The injection is given into a muscle (known as an intramuscular injection).

You may have some pain, swelling or itching where your injection was given. However this is usually mild and will wear off quite quickly.

Will my dose go up or down?

When you first start having your treatment, you'll usually have an injection a few times a week.

Your dose may go up or down, depending on your response to the treatment and the vitamin B12 levels in your blood.

To see how well it's working, your doctor will ask you about your symptoms such as tiredness and lack of energy. They will also give you regular blood tests to monitor the vitamin B12 levels in your blood.

As your symptoms and vitamin B12 levels improve, you may be able to have the injections less often, such as every few months.

How long will I take it for?

Your doctor will decide exactly how long you will need to have hydroxocabalamin injections. It depends on how well you respond to your treatment.

What if I miss an appointment?

It's important to attend your appointments.

If you miss having your injection, the level of vitamin B12 in your body will go down further. This may make your health problems worse.

If you do have to miss an appointment, ask your doctor or nurse when you should have the next dose.

Side effects

Like all medicines, hydroxocobalamin can cause side effects in some people, but not everyone gets them.

Common side effects

Talk to your doctor if any of these side effects bother you or do not go away after a few days:

  • pain, swelling or itchy skin where your injection was given
  • feeling or being sick (nausea or vomiting)
  • diarrhoea
  • headaches
  • feeling dizzy
  • hot flushes

Serious side effects

Serious side effects are very rare but tell your doctor immediately if you get any of these symptoms after having treatment:

  • irregular heartbeats or heartbeats that suddenly become more noticeable (palpitations)

Serious allergic reaction

In rare cases, hydroxocobalamin can cause a serious allergic reaction (anaphylaxis).

Call your local emergency service if:

  • you get a skin rash that may include itchy, red, swollen, blistered or peeling skin
  • you're wheezing
  • you get tightness in the chest or throat
  • you have trouble breathing or talking
  • your mouth, face, lips, tongue or throat start swelling

You could be having a serious allergic reaction and may need immediate treatment in hospital.

These are not all the side effects of hydroxocobalamin. For a full list, see the leaflet inside your medicines packet.

How to cope with side effects

What to do about:

  • pain, swelling or itchy skin where your injection was given - these symptoms are usually mild and should only last a few hours. You can ask a pharmacist to recommend a mild painkiller if the pain is bothering you
  • feeling or being sick - stick to simple meals and avoid rich or spicy food. If you're being sick, try small, frequent sips of water to avoid dehydration
  • diarrhoea - drink plenty of fluids, such as water or squash, to avoid dehydration. Signs of dehydration include peeing less than usual or having dark strong-smelling pee
  • headaches - make sure you rest and drink plenty of fluids. Do not drink too much alcohol. Ask your pharmacist to recommend a painkiller. Talk to your doctor if the headaches are severe or last longer than a few days
  • feeling dizzy - stop what you're doing, and sit or lie down until you feel better. Do not drive, ride a bike or use tools or machinery until you stop feeling dizzy
  • hot flushes - try cutting down on coffee, tea and alcohol. It might help to keep the room cool and use a fan. You could also spray your face with cool water or sip cold or iced drinks. The flushing should go away after a few days. If it does not go away, or if it's causing you problems, contact your doctor

Pregnancy and breastfeeding

Hydroxocobalamin is generally safe to have in pregnancy and while you're breastfeeding.

Hydroxocobalamin does pass into your milk, but it's not harmful to your baby.

For more information about how vitamin B12 treatments can affect you and your baby during pregnancy, read this leaflet on the Best Use of Medicines in Pregnancy (BUMPS) website.


Tell your pharmacist or doctor if you're trying to get pregnant, already pregnant or breastfeeding.

Cautions with other medicines

Hydroxocobalamin is usually safe to have with other medicines including painkillers.

Mixing hydroxocobalamin with herbal remedies and supplements

There's very little information about taking herbal remedies and supplements while taking or using hydroxocobalamin.


For safety, tell your doctor or pharmacist if you're taking any other medicines, including herbal remedies, vitamins or supplements.

Common questions