Like all medicines, ferrous sulfate can cause side effects in some people, but many people have no side effects or only minor ones.
Common side effects
There are things you can do to cope with these common side effects of ferrous sulfate:
Feeling or being sick (nausea or vomiting)
Try taking ferrous sulfate with, or just after, a meal or snack. Stick to simple meals and do not eat rich or spicy food. 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 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.
Stomach discomfort or heartburn
Try taking ferrous sulfate with, or just after, a meal or snack. It can help to eat and drink slowly and have smaller and more frequent meals.
Losing your 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.
Constipation
To help with constipation, get more fibre into your diet by eating fresh fruit, vegetables and cereals, and drink plenty of water. Try to exercise more regularly, for example, by going for a daily walk or run.
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 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.
Darker than usual poo
This is common when taking iron and is usually nothing to worry about.
Black stained teeth
Rinse your mouth with water after taking the drops. Do not suck or chew the tablet, or keep it in your mouth.
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
Talk to a doctor or call 111 straight away if your poo is black, tar-like or red, or has blood in or on it, or if you also feel unwell in any other way.
Serious allergic reaction
In rare cases it's possible to have a serious allergic reaction (anaphylaxis) to ferrous sulfate.
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 ferrous sulfate. For a full list, see the leaflet inside your medicines packet.
You can report any suspected side effect using the Yellow Card safety scheme.