Ferrous sulphate is the standard iron supplement — used to treat and prevent iron deficiency and iron deficiency anaemia. It is the cheapest and most effective form of oral iron, and also the one most likely to upset your stomach. Both facts matter when choosing.
What is Ferrous Sulfate?
Ferrous sulphate (also spelled sulfate) is an iron salt — iron combined with sulphate — and it is the reference standard against which every other oral iron is compared.
It appears on the South African Medicine Price Registry mainly as an ingredient inside multivitamin and antenatal combinations such as Complenatal FF, which contains ferrous sulphate 150 mg alongside folic acid and B vitamins. Plain ferrous sulphate tablets are widely available from pharmacies and clinics, often unbranded and inexpensive.
Two numbers appear on iron packaging, and confusing them is the commonest error.
Ferrous sulphate 200 mg contains roughly 65 mg of elemental iron. The larger number is the weight of the whole compound; the elemental iron figure is what your body actually receives, and it is the only number worth comparing between products. A supplement advertising “300 mg iron” may deliver less elemental iron than one advertising 200 mg, depending on the salt used.
Why ferrous sulphate specifically. Iron is absorbed as ferrous iron (Fe²⁺), not ferric (Fe³⁺). Ferrous salts release it in that readily absorbed form, and sulphate is the cheapest and among the best absorbed — which is why it remains first-line worldwide.
The trade-off is tolerance. Ferrous sulphate releases iron quickly in the stomach, and free iron there irritates the gut lining. Nausea, cramping, constipation and dark stools are common — enough that a significant proportion of people stop taking it. Gentler forms exist — iron polymaltose (Ferrimed) and ferrous fumarate among them — but studies generally find ferrous salts raise haemoglobin at least as fast. The practical rule: the best iron is the one you keep taking.
What is Ferrous Sulfate commonly used for?
- Iron deficiency anaemia — low iron has reduced haemoglobin, causing tiredness, breathlessness on exertion, pallor and poor concentration.
- Iron deficiency without anaemia, where stores are low but haemoglobin has not yet fallen. This causes fatigue on its own and is frequently missed.
- Pregnancy, where iron requirements rise substantially — hence its presence in antenatal combinations.
- Heavy menstrual periods, the commonest cause of iron deficiency in women of reproductive age.
- After significant blood loss, including surgery or trauma.
- Poor absorption — coeliac disease, after stomach surgery, or on long-term acid-suppressing medicines.
- Vegetarian and vegan diets, where plant iron is less well absorbed, and frequent blood donors.
- Restless legs syndrome, genuinely associated with low iron stores and often improved when they are corrected.
Two points matter more than any dose or brand.
Iron deficiency is a symptom, not a diagnosis. Iron is lost, not used up. In an adult — especially a man, or a woman past menopause — new iron deficiency needs the cause investigated, because slow bleeding from the gut is one explanation and can be the first sign of something that needs finding early.
Treatment takes months. Haemoglobin usually starts recovering within two to four weeks, but refilling the body’s iron stores takes roughly three further months after that. Stopping as soon as you feel better is the commonest reason deficiency returns.
Who commonly looks for Ferrous Sulfate and why
People told they are anaemic — from a routine blood test, a donation deferral, or an investigation into fatigue.
Pregnant women, for whom iron is standard antenatal care in South Africa, and people with heavy periods, often after years of unexplained tiredness.
People who could not tolerate iron before and want something different — or who found a gentler iron too expensive and want the cheap standard.
People who are exhausted and suspect low iron. Fatigue has many causes — thyroid problems, sleep apnoea, depression, diabetes, other anaemias. A blood test finds which. Taking iron you do not need is not harmless.
Athletes, particularly distance runners and menstruating women, where low iron stores measurably reduce performance.
What to check on the label before taking Ferrous Sulfate
- Elemental iron content. The figure that matters. Ferrous sulphate 200 mg gives roughly 65 mg elemental iron.
- Whether it is plain iron or a combination. Antenatal and multivitamin products contain iron alongside folic acid and B12 — check you are not doubling up.
- Whether it is modified-release, which is gentler but often delivers iron past the part of the gut where absorption is best.
- Whether it contains vitamin C, which improves absorption.
Store iron where children cannot reach it. Iron overdose is a leading cause of poisoning deaths in young children, and a small number of adult tablets can cause serious harm. Sweet syrups and coated tablets are exactly what a child will take willingly. This is not a routine caution.
Safety, interactions and when to seek professional advice
Take it on an empty stomach if you can tolerate it — about an hour before food — since food substantially reduces absorption. If that causes nausea, taking it with a little food is better than stopping. Vitamin C improves absorption; a glass of orange juice is a reasonable habit.
Taking it every other day may work as well as daily, and be better tolerated. Recent evidence suggests alternate-day dosing gives comparable absorption with fewer side effects, because a large dose transiently blocks absorption of the next one. Worth discussing with your doctor.
Space it by at least two hours from: tea, coffee and milk, which markedly reduce absorption; calcium supplements and antacids; proton pump inhibitors; thyroid medicine (levothyroxine), which is clinically important; tetracycline and quinolone antibiotics such as doxycycline and ciprofloxacin, which iron binds so neither works; and bisphosphonates, methyldopa, levodopa and penicillamine.
Do not take iron without a confirmed need if you have haemochromatosis or any iron-overload condition, or receive regular transfusions. Extra iron is actively harmful in these.
Tell a pharmacist or doctor if you have inflammatory bowel disease, stomach ulcers or kidney disease, or already take another iron-containing supplement.
Common effects: nausea, stomach discomfort, constipation and, less often, diarrhoea. Constipation usually responds to more fluid and fibre.
Expect dark or black stools. This is normal and harmless — unabsorbed iron. But black tarry stools with a strong smell, or feeling faint or unwell, can indicate bleeding in the gut, so do not assume it is the tablets.
Seek advice promptly for severe abdominal pain, vomiting, black tarry stools with feeling unwell, or a rash. Get emergency help for any suspected overdose, particularly in a child, even if they seem fine — take the packaging.
See a doctor if your fatigue does not improve after a few weeks, if a repeat blood test shows no response, if you cannot tolerate iron at all, or if the cause of the deficiency has not been investigated — particularly in men and post-menopausal women, who should be assessed rather than simply supplemented.
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Frequently asked questions
What is ferrous sulphate used for? Treating and preventing iron deficiency and iron deficiency anaemia.
What are ferrous sulphate tablets used for? The same — correcting low iron, whether from heavy periods, pregnancy, blood loss, poor absorption or diet.
How much iron is in a 200 mg tablet? Roughly 65 mg of elemental iron. That elemental figure is the one to compare between products.
How long do I take it? Usually several months. Haemoglobin recovers in weeks, but refilling iron stores takes about three months more. Stopping early is why deficiency returns.
Why does it upset my stomach? Ferrous sulphate releases iron quickly, and free iron irritates the gut lining. Taking it with a little food, or every other day, often helps — and a gentler form such as iron polymaltose is an alternative.
Why are my stools black? Unabsorbed iron. Normal. But black tarry stools with feeling unwell can indicate bleeding, so get that checked.
Can I take it with my thyroid tablet? Not at the same time. Separate them by at least two hours — iron significantly reduces levothyroxine absorption.
Can I take it with tea or coffee? Not at the same time. Both markedly reduce absorption. Vitamin C improves it.
Should I take iron if I am just tired? Get a blood test first. Fatigue has many causes, and taking iron you do not need is not harmless.