Ferrous Sulfate: Uses, Benefits, Dosage & Safety
Last updated: August 2026 · Reviewed by the FactoWiki Editorial Team for clarity and source accuracy
Quick summary
Ferrous sulphate is the cheapest and most-studied iron supplement and the standard first-line treatment for iron deficiency anaemia. It also causes constipation, nausea and dark stools in a large proportion of people, which is the main reason courses get abandoned.
What is Ferrous Sulfate?
Iron in the ferrous (Fe2+) form bound to sulphate. A standard 325 mg tablet supplies roughly 65 mg elemental iron. It is the reference form against which other iron supplements are compared, and it is what most clinical guidelines specify.
What Ferrous Sulfate is commonly used for
Iron deficiency anaemia, iron deficiency without anaemia, pregnancy, and repletion after blood loss.
How Ferrous Sulfate works
Ferrous iron is absorbed in the duodenum via the DMT1 transporter and incorporated into haemoglobin. Absorption is regulated by hepcidin, which rises after a dose and suppresses further absorption for around 24 hours — the physiological basis for alternate-day dosing outperforming daily dosing.
What the evidence says
Each claim below is tied to the specific study behind it, rather than to a general reading list.
- Alternate-day dosing produces higher fractional iron absorption than daily dosing. Stoffel et al., Lancet Haematology, 2017 — randomised controlled trial. (PMID 29032957)
- Lower-dose iron is as effective as higher doses with fewer side effects. Rimon et al., American Journal of Medicine, 2005 — randomised trial in older adults. (PubMed)
- Iron ingestion is a leading cause of poisoning fatality in young children. Poison control surveillance data. (PubMed)
Typical dosage used in studies
65 mg elemental daily is standard, though evidence increasingly supports lower doses or alternate-day schedules, which absorb proportionally better and cause fewer side effects. Take with vitamin C, away from tea, coffee, calcium and dairy.
Side effects and safety
Constipation, nausea, abdominal pain and black stools are common and dose-related. Iron tablets are among the leading causes of fatal poisoning in children under six — store them out of reach and in child-resistant packaging. Never supplement without confirmed deficiency.
Medication interactions and who should avoid Ferrous Sulfate
Medication & safety check
Reduces absorption of levothyroxine, quinolones, tetracyclines, bisphosphonates, levodopa and methyldopa — separate by two hours minimum. PPIs, calcium, tea and coffee reduce iron absorption. Contraindicated in haemochromatosis and other iron overload states.
General information, not personal medical advice. If you take any medication, confirm it is safe to combine with Ferrous Sulfate with your doctor or pharmacist first.
Sources & further reading
The claim-level citations above are drawn from these sources:
- Stoffel et al., Lancet Haematology, 2017 — randomised controlled trial — PMID 29032957
- Rimon et al., American Journal of Medicine, 2005 — randomised trial in older adults — find on PubMed
- Poison control surveillance data — find on PubMed
- NIH Office of Dietary Supplements
- NIH National Center for Complementary and Integrative Health
Frequently asked questions
Why do my stools turn black?
Unabsorbed iron reacts in the gut. It is harmless and expected. Black tarry stools with a foul smell are different and can indicate bleeding — see a doctor.
Can I take it with food to avoid nausea?
It reduces absorption but improves tolerance. If the alternative is stopping altogether, taking it with food is the better trade.
How long until my levels recover?
Haemoglobin typically responds within 2–4 weeks, but ferritin stores take 3–6 months to refill. Do not stop early.
Part of a wider guide
Ferrous Sulfate is one form of Iron. This page covers what is specific to this form — absorption, tolerability, dosing and who it suits. For the underlying nutrient itself, its overall evidence base and general safety, read the Iron guide.
Where you'll find Ferrous Sulfate
Ferrous Sulfate appears in Minerals & Anaemia formulas. Browse the supplement guides to see the products we review, each with a full breakdown of formula, pricing and safety.
Related ingredients to explore
Ingredients often studied or formulated alongside Ferrous Sulfate.
General information, not medical advice.