Like all medicines, hydroxocobalamin can cause side effects in some people, but not everyone gets them.
Common side effects
There are things you can do to help cope with these common side effects of hydroxocobalamin:
Pain, swelling or itchy skin where you had the injection
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 (nausea or vomiting)
Stick to simple meals and avoid rich or spicy food. If you're being sick, try small, frequent sips of water to avoid dehydration.
If you take the combined contraceptive pill or the progestogen-only pill and you're being sick, your contraception may not protect you from pregnancy. Check the pill packet for advice.
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.
If you take the combined contraceptive pill or the progestogen-only pill and you have severe diarrhoea for more than 24 hours, your contraception may not protect you from pregnancy. Check the pill packet for advice.
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 alcohol and drinks containing caffeine, such as tea, coffee, cola and energy drinks. It might help to use a fan to keep the room cool. 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.
Speak to a doctor or pharmacist if the advice on how to cope does not help and a side effect is still bothering you or does not go away.
Serious side effects
Serious side effects are very rare.
Tell your doctor or call 111 immediately if you get irregular heartbeats or heartbeats that suddenly become more noticeable (palpitations) after having treatment.
As hydroxocobalamin contains cobalt, it can cause sensitivity reactions in people who have an allergy to cobalt. Symptoms can start straight away or up to 3 days after having a dose. Talk to your doctor or call 111 if you get an allergic skin reaction such as a rash or hives.
Serious allergic reaction
In rare cases, hydroxocobalamin can cause a serious allergic reaction (anaphylaxis).
Immediate action required: Call 999 now if:
- your lips, mouth, throat or tongue suddenly become swollen
- you're breathing very fast or struggling to breathe (you may become very wheezy or feel like you're choking or gasping for air)
- your throat feels tight or you're struggling to swallow
- your skin, tongue or lips turn blue, grey or pale (if you have black or brown skin, this may be easier to see on the palms of your hands or soles of your feet)
- you suddenly become very confused, drowsy or dizzy
- someone faints and cannot be woken up
- a child is limp, floppy or not responding like they normally do (their head may fall to the side, backwards or forwards, or they may find it difficult to lift their head or focus on your face)
You or the person who's unwell may also have a rash that's swollen, raised, itchy, blistered or peeling.
These can be signs of a serious allergic reaction and may need immediate treatment in hospital.
Do not drive yourself to A&E.
The person you speak to at 999 will give you advice about what to do.
Other side effects
These are not all the side effects of hydroxocobalamin. For a full list, see the leaflet inside your medicine's packet.
Reporting side effects
You can report any suspected side effect using the Yellow Card safety scheme.
Visit the Yellow Card website for more information about reporting side effects.