Like all medicines, nitrofurantoin can cause side effects, although not everyone gets them.
Common side effects
There are things you can do to help cope with these common side effects of nitrofurantoin.
Feeling sick (nausea)
Taking nitrofurantoin with or after a meal or snack should help prevent this. It may also help if you avoid rich or spicy food.
Being sick (vomiting)
Have frequent sips of fluids, such as water or squash, to avoid dehydration. Signs of dehydration include peeing less than usual or having strong-smelling pee. Do not take any other medicines to treat vomiting without speaking to a pharmacist or doctor.
If you take contraceptive pills 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 strong-smelling pee. Do not take any other medicines to treat diarrhoea without speaking to a pharmacist or doctor.
If you take contraceptive pills and you have severe diarrhoea for more than 24 hours, your contraception may not protect you from pregnancy. Check the pill packet for advice.
Loss of appetite
Eat when you would usually expect to be hungry. If it helps, eat smaller meals more often than usual. Snack when you're hungry. Have nutritious snacks that are high in calories and protein, such as dried fruit and nuts.
Headaches
Make sure you rest and drink plenty of fluids. Do not drink too much alcohol. Painkillers you can buy without a prescription, such as paracetamol and ibuprofen, are safe to take with nitrofurantoin. Speak to your doctor if these do not help or the headaches are severe.
Dizziness or feeling sleepy
If nitrofurantoin makes you feel dizzy, stop what you're doing and sit or lie down until you feel better. Do not drive a car or ride a bike while you're feeling dizzy or sleepy.
Keep taking the medicine, but speak to a doctor if the advice on how to cope does not help and a side effect is still bothering you or does not go away.
Nitrofurantoin may cause your pee to turn dark yellow or a brownish colour. This is normal and is not a reason to stop taking the medicine. Your pee will return to its usual colour once you stop taking nitrofurantoin.
Serious side effects
Serious side effects are rare and happen in less than 1 in 1,000 people.
Call a doctor or call 111 straight away if you have:
- a cough, coughing up blood or mucus, shortness of breath, pain when you breathe or a high temperature – these can be signs of lung problems
- pale poo and dark pee together, or the whites of your eyes turn yellow or your skin turns yellow (this may be less obvious on brown or black skin) – this can be a sign of liver or gallbladder problems
- bruising or bleeding you cannot explain (including nosebleeds), sore throat, a high temperature and feeling tired or generally unwell – these can be signs of blood problems
- severe headaches
Immediate action required: Call 999 or go to A&E if:
- you get chest pain or difficulty breathing – these can be signs of lung problems
- you get pins and needles, tingling sensations, numbness or weakness – these can be signs of nerve problems
Serious allergic reaction
In rare cases, it's possible to have a serious allergic reaction to nitrofurantoin (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.
Other side effects
These are not all the side effects of nitrofurantoin. For a full list see the leaflet inside your medicines packet.
You can report any suspected side effect using the Yellow Card safety scheme.