It's unusual to have side effects when using metronidazole cream or gel. But there can be some common side effects with the tablets, liquid, suppositories or vaginal gel.
Do not drink alcohol while taking the tablets or liquid or using the vaginal gel or suppositories. It can give you severe side effects such as feeling or being sick, stomach pain, hot flushes, difficulty breathing, a pounding heartbeat (palpitations) and headaches.
After finishing your treatment, wait for 2 days before drinking alcohol again. This allows the metronidazole to leave your body.
Common side effects of tablets, liquid, suppositories or vaginal gel
Keep taking the medicine, but talk to your doctor or pharmacist if these side effects of metronidazole bother you or do not go away. There are things you can do to help cope with them:
Feeling or being sick (nausea or vomiting)
Stick to simple meals and do not eat rich or spicy food. Always try to take your metronidazole after a meal or snack. If you're being sick, try small frequent sips of water to avoid dehydration. Signs of dehydration include peeing less than usual or having dark, strong-smelling pee. If you're being sick for more than 24 hours contact your doctor for advice.
If you take the combined 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 that usual or having dark, strong-smelling pee.
If your diarrhoea continues for more than 24 hours contact your doctor for advice. Do not take any other medicines to treat diarrhoea without speaking to a pharmacist or doctor.
If you take the combined pill or progestogen-only pill and you have severe diarrhoea, your contraception may not protect you from pregnancy. Check the pill packet for advice.
A metallic taste in your mouth or a furry tongue
Drink plenty of water and eat plain foods that you usually enjoy. If your tongue is very furry, this could be a sign of thrush – ask your pharmacist or doctor for advice.
Serious side effects of tablets, liquid, suppositories or vaginal gel
Serious side effects are rare and happen in less than 1 in 1,000 people.
Call a doctor or call 111 straight away if:
- the whites of your eyes turn yellow, or your skin turns yellow although this may be less obvious on brown or black skin – these can be signs of liver or gallbladder problems
- you get unexpected infections, mouth ulcers, bruising, bleeding gums, or extreme tiredness – these can be caused by a blood problem
- you have bad stomach pains which may reach through to your back – this can be a sign of pancreatitis
- you have blurred vision or double vision
Immediate action required: Call 999 or go to A&E if:
- you have a stiff neck
- you have a dislike of bright lights
- you're seeing or hearing things that are not there (hallucinating)
- you're feeling confused or having difficulty speaking
You may also have a temperature.
These can be signs of meningitis or signs that metronidazole is affecting your brain.
Do not drive to A&E. Ask someone to drive you or call 999 and ask for an ambulance.
Bring all the medicines you take with you.
Serious allergic reaction
In rare cases, it's possible to have a serious allergic reaction (anaphylaxis) to metronidazole.
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 metronidazole tablets, liquid, cream, gel, suppositories or vaginal gel. For a full list see the leaflet inside your medicines 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.