Ferrous sulfate: iron tablets and drops explained

Iron is needed to make red blood cells, which carry oxygen around the body. Ferrous sulfate replaces iron when stores have run low. The NHS says low iron can follow blood loss, pregnancy or a diet short of iron, and the medicine is used both to treat established iron deficiency anaemia and to prevent it in people at risk.

It comes as tablets or as drops that are swallowed. It is available on prescription and from pharmacies.

The NHS says most adults and some children aged 12 and over can take ferrous sulfate with the advice of a doctor or pharmacist. Younger children are dosed by age and weight.

It is not suitable for everyone. Tell the doctor or pharmacist if any of these apply:

• You have had an allergic reaction to ferrous sulfate or another medicine.

• Your anaemia is not caused by lack of iron.

• You have haemochromatosis or haemosiderosis, which are conditions of iron overload.

• You have sickle cell anaemia or thalassaemia.

• You have a stomach ulcer, have had all or part of your stomach removed, or have other stomach or bowel problems.

• You have had repeated blood transfusions, or blood in your urine.

• You are already being treated for iron deficiency.

For treating iron deficiency in adults the NHS gives one 200mg tablet a day, or 2 to 3 times a day depending on instructions, with every-other-day dosing possible if side effects trouble you. Adult drops are 4ml once or twice a day. For prevention in adults it is one 200mg tablet once a day, or 2.4ml to 4.8ml of drops once daily. Doses for children aged 12 to 17 are based on age and blood results, and for under-12s on age and weight. Your own label is what to follow.

Ferrous sulfate works best on an empty stomach, which means 30 minutes before eating or 2 hours after. If it upsets your stomach it can be taken with food. Swallow tablets whole with water without sucking, chewing or holding them in the mouth, and measure drops with the syringe or dropper supplied, never a kitchen teaspoon.

Keep tea, coffee, milk, dairy and eggs at least 2 hours away from a dose, because they reduce how much iron you absorb. Taking it with orange juice or a vitamin C supplement is suggested.

Treatment usually lasts several months and carries on for 3 to 6 months after improvement; prevention continues as long as you remain at risk. A missed dose should be skipped if the next is almost due, and you should never double up.

Most people start to feel better after 3 to 4 weeks, but it can take up to 2 to 4 months for the medicine to work fully. That is why courses run on for months. Stopping when you first feel better would leave stores only partly rebuilt, so follow your doctor's advice on duration.

Iron-rich foods help too: the NHS lists leafy greens, fortified cereals, meat, pulses, nuts, dried fruit and wholegrains.

Common effects are nausea or vomiting, stomach discomfort or heartburn, loss of appetite, constipation, diarrhoea, darker than usual stools and, with drops, black-stained teeth. Darker stools are common on iron and usually nothing to worry about.

• Nausea: try taking it with or just after a meal or snack.

• Constipation: increase fibre and water, and exercise regularly.

• Diarrhoea: keep drinking fluids and ask a professional before self-treating.

• Teeth staining: rinse your mouth after drops and do not chew or suck tablets.

• Black, tar-like or bloody stools with feeling unwell need a call to a doctor or pharmacist.

• Swollen lips, mouth, throat or tongue, severe breathing difficulty or collapse need 999.

Iron can interfere with, or be interfered with by, a long list of medicines. The NHS names the antibiotics oxytetracycline, doxycycline, ciprofloxacin and chloramphenicol; the HIV medicines bictegravir and dolutegravir; levothyroxine; the Parkinson's medicines levodopa, carbidopa and entacapone; the bone medicines alendronic acid and risedronate; and others such as cholestyramine, eltrombopag, mycophenolate, methyldopa, penicillamine and trientine. Antacids, other indigestion remedies, magnesium hydroxide laxatives and calcium, magnesium, zinc or other iron supplements also interact. A gap between iron and any other medicine is sensible.

Taking more than the recommended amount needs a call to NHS 111, since serious overdose can cause vomiting blood, seizures or unconsciousness. Keep it away from children.

Iron supplements are safe in pregnancy and may be recommended when blood tests show low iron; constipation and haemorrhoids are common then and can be managed. They are safe while breastfeeding, although a parent taking iron will not treat low iron in a baby. There is no evidence of an effect on fertility.

Alcohol is permitted and ferrous sulfate does not impair driving or cycling. Suspected side effects can be reported through the Yellow Card scheme.