Ferrous sulfate

What it is

Ferrous sulfate is an oral iron salt sold over the counter. The iron it supplies is absorbed in the upper small intestine and used to build haemoglobin and to refill body iron stores. It is taken for iron deficiency, with or without anaemia.

A usual adult range, not a national label — the dose and the timing differ by country and by product.

Used for

• Deficiency

Approved uses differ by country — some of these may be off-label or unapproved where you live.

What to know while taking it

Absorption is best on an empty stomach and is helped by vitamin C, while tea, coffee, and calcium-containing supplements bind iron in the gut and blunt it. Iron also binds several medicines and reduces their absorption, so levothyroxine, doxycycline and ciprofloxacin need separating in time from it, and omeprazole lowers the stomach acid iron needs; it competes with zinc as well. Dark stool is expected and harmless, constipation is common, and ferritin, haemoglobin, serum iron and transferrin saturation are the values used to judge the response.

When to see a doctor

See a doctor if abdominal pain, vomiting, or black tarry stool with lightheadedness occurs, since that suggests bleeding rather than the harmless darkening, and if fatigue or blood counts do not improve, since unexplained iron deficiency needs its cause found.

Worth knowing

• Vitamin C improves absorption
• Tea and coffee block absorption
• Dark stool is normal
• Can cause constipation

Markers to watch

• Ferritin
• Hemoglobin
• Serum iron
• Transferrin saturation

Nutrients affected

• zinc — absorption blocked with (Free T3, Testosterone, TSH)