Common side effects
These common side effects of clarithromycin happen in more than 1 in 100 people. There are things you can do to help cope with them:
Feeling sick (nausea)
Stick to simple meals and do not eat rich or spicy food while you're taking this medicine. It might help to take your clarithromycin after you have a meal or snack.
Being sick (vomiting)
Try taking small, frequent sips of water to avoid dehydration. Signs of dehydration include peeing less than usual or having dark, strong-smelling pee. Do not take any other medicines to treat vomiting without speaking to a pharmacist or doctor.
If you take the combined contraceptive pill or progestogen-only pill and you're being sick, your contraception may not protect you from pregnancy. Check the pill packet for advice.
Diarrhoea
Drink lots of fluids, such as water or squash, to avoid dehydration. Signs of dehydration include peeing less than usual or having dark, strong-smelling pee. Do not take any other medicines to treat diarrhoea without speaking to a pharmacist or doctor.
If you take the combined contraceptive pill or 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.
Bloating and indigestion
Try not to eat foods that cause farting (flatulence) like lentils, beans and onions. Eat smaller meals, eat and drink slowly, and exercise. There are pharmacy medicines that can also help, such as antacids or simeticone. Ask a pharmacist for advice.
Headaches
Rest and drink plenty of fluids. It's best not to drink too much alcohol. Ask your pharmacist to recommend a painkiller if you need one. Talk to your doctor if the headaches last longer than a week or are severe.
Difficulty sleeping (insomnia)
Avoid having a big meal, smoking, and drinking alcohol, tea or coffee in the evening. Try not to watch television or use your mobile phone before going to bed. Instead, try to relax for an hour before bedtime.
If this advice does not help and any of these side effects continue to bother you, keep taking the medicine, but tell your doctor or pharmacist.
Serious side effects
Serious side effects are rare and happen in less than 1 in 1,000 people.
Call a doctor or call 111 now if you get:
- a faster or irregular heartbeat
- pale poo, dark pee and a yellow colour to the whites of your eyes or skin (although this may be less obvious on brown or black skin) – these can be signs of liver problems
- severe pain in your stomach and/or back – this can be a sign of inflammation of the pancreas (pancreatitis)
- diarrhoea (perhaps with muscle cramps) that contains blood or mucus – if you have severe diarrhoea without blood or mucus for more than 4 days, also speak to a doctor
- hallucinations (seeing or hearing things that are not there)
Serious allergic reaction
In rare cases, it's possible to have a serious allergic reaction (anaphylaxis) to clarithromycin.
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.
Other side effects
These are not all the side effects of clarithromycin. For a full list, see the leaflet inside your medicine packet.
You can report any suspected side effect using the Yellow Card safety scheme.