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Ferrous sulfate: 7 things you should know

Medically reviewed by Carmen Pope, BPharm. Last updated on Aug 30, 2023.

1. How it works

  • Ferrous sulfate is an iron salt that is commonly used as an iron supplement.
  • Iron supplements are used to treat or prevent iron-deficiency anemia. In iron deficiency anemia, a lack of iron reduces the production of hemoglobin. Hemoglobin allows red blood cells to transport oxygen around the body as well as giving red blood cells their color.
  • Only the iron component of the iron salt is utilized; therefore, iron supplements usually state the amount of the iron salt (for example, ferrous sulfate 325mg) and the equivalent amount of elemental iron (for ferrous sulfate 325mg this equates to 65mg of elemental iron).
  • Ferrous sulfate is a mineral and it belongs to the group of medicines known as iron supplements.

2. Upsides

  • Ferrous sulfate is an iron supplement that may be used to reverse or prevent anemia and replenish iron stores.
  • May be used to aid dietary needs.
  • May be used off-label to treat restless legs syndrome.
  • Although only 10-15% of ferrous sulfate is absorbed, this rate is comparable to that of ferrous gluconate and ferrous fumarate. All of the iron salts have a similar rate of gastrointestinal side effects.
  • Ferrous sulfate is usually inexpensive.
  • Available as capsules, tablets, and a liquid.
  • Immediate-release preparations are preferred for the treatment of iron deficiency anemia because enteric-coated or extended-release preparations are poorly absorbed.
  • Generic ferrous sulfate is available.

3. Downsides

If you are between the ages of 18 and 60, take no other medication or have no other medical conditions, side effects you are more likely to experience include:

  • Abdominal discomfort, black or dark stools, constipation, diarrhea, heartburn, nausea, and vomiting, are the most common side effects. The risk of side effects increases with higher dosages.
  • The optimal duration of iron supplementation is not known; however, most experts recommend continuing iron supplementation for three months after normalization of hemoglobin to replenish iron stores.
  • Accidental ingestion of iron supplements, such as ferrous sulfate, is a leading cause of deadly poisoning in children younger than 6 years old. Advise all people taking iron supplements to keep them out of reach of children, and if ingested accidentally, to contact a poison control center immediately.
  • Few studies have been conducted on the safety and efficacy of iron supplements, including ferrous sulfate. However, a select committee on Generally Recognized as Safe (GRAS) substances concluded that there is no reason to suspect iron supplements are a hazard to the public when they are used as they are now used in current practice. Ferrous sulfate is not FDA-approved.
  • The low absorption rate of ferrous sulfate and other iron salts means that three times daily dosing may be necessary to reverse iron deficiency.
  • Enteric-coated preparations may not be as well absorbed as well as liquid preparations.
  • Iron supplements may not be suitable for people with a history of ulcers, colitis, or intestinal disease. People with porphyria, thalassemia, or hemolytic anemia, who excessively drink alcohol, or women who are pregnant should talk to their doctor before taking iron supplements.
  • Ferrous sulfate liquid may cause discoloration of teeth.
  • Should not be given to people receiving frequent blood transfusions. Avoid in premature infants until vitamin E stores (deficient at birth) are replenished.
  • Ferrous sulfate tablets are not recommended for children aged less than twelve.
  • May interact with several other medications including some antibiotics, antacids, and other supplements, particularly those that contain calcium, phosphorous, or zinc.
  • Maternal iron requirements increase during pregnancy and untreated iron deficiency may be associated with adverse fetal events, such as low birth weight, premature delivery, or increased perinatal mortality.

Note: In general, seniors or children, people with certain medical conditions (such as liver or kidney problems, heart disease, diabetes, seizures) or people who take other medications are more at risk of developing a wider range of side effects. View complete list of side effects

4. Bottom Line

  • Ferrous sulfate is an iron supplement that may be used to prevent or treat iron-deficiency anemia. Gastrointestinal side effects are common.

5. Tips

  • Ferrous sulfate is available as regular, coated, extended-release tablets and capsules and also as an oral liquid. Swallow iron tablets and capsules whole; do not crush, open, or chew.
  • The usual dosage of ferrous sulfate for iron deficiency is three times daily, one hour before or two hours after meals. However, your doctor may advise a lower dosage for you if you are older or if you develop significant gastrointestinal side effects. Follow your doctor's instructions.
  • Administering iron with meals impairs absorption by about 50% and it is uncertain whether this resolves any gastrointestinal side effects.
  • Some iron products contain tartrazine. If you are allergic to tartrazine, tell your doctor.
  • Even though your iron deficiency may resolve within a few weeks, take ferrous sulfate for the recommended duration to ensure your iron stores are replenished.
  • Use the dropper provided with ferrous sulfate drops to measure the correct dose. Place the drops directly in the mouth or mix with water or fruit juice (do not use milk).
  • Taking iron supplements with vitamin C may help improve absorption rates by as much as 48%.
  • Iron supplements, including ferrous sulfate, may interact with some medications including some antibiotics, antacids, and other supplements. These medicines need to be separated by several hours to ensure adequate iron absorption. Talk with your pharmacist about how best to space your medicines.
  • Ferrous sulfate should be taken in conjunction with dietary changes that ensure your diet contains adequate amounts of iron-rich seafood or vegetables, meat (particularly red meat), and iron-fortified foods.
  • Mixing liquid ferrous sulfate with water or fruit juice and then sipping the mixture through a straw may help prevent teeth staining. Baking soda rubbed on the teeth once a week may help limit any staining that does occur.
  • Keep iron supplements well out of reach of children as accidental iron overdosage in children is common and can be fatal.
  • Do not take iron supplements for longer than 6 months unless your doctor has advised you to do so.
  • Do not take any other medications including those bought over the counter without first checking with your doctor or pharmacist that they are compatible with ferrous sulfate because it may prevent other medications from being absorbed by the body.
  • Tell your doctor if you are breastfeeding, pregnant, or intending to become pregnant because you will need to discuss the benefits and risks of using iron supplements during pregnancy and breastfeeding.

6. Response and effectiveness

  • A rise in hemoglobin levels should be expected within three weeks of therapy. An increase in hemoglobin by 1g/dL after one month is considered an adequate response. However, experts recommend therapy continue for at least three months to replenish iron stores.

7. Interactions

Medicines that interact with ferrous sulfate may either decrease its effect, affect how long it works, increase side effects, or have less of an effect when taken with ferrous sulfate. An interaction between two medications does not always mean that you must stop taking one of the medications; however, sometimes it does. Speak to your doctor about how drug interactions should be managed.

Common medications that may interact with ferrous sulfate include:

  • alpha-lipoic acid
  • antacids, such as those that contain aluminum, calcium, magnesium, or sodium bicarbonate
  • antibiotics, such as doxycycline, minocycline, and tetracycline
  • bisphosphonates, such as alendronate, risedronate
  • cefdinir (may make stools appear red)
  • chloramphenicol
  • cimetidine
  • dimercaprol
  • HIV medications, such as bictegravir, dolutegravir, emtricitabine, or tenofovir
  • levothyroxine
  • other iron-containing substances, such as iron dextran, iron sucrose, and ferric carboxymaltose
  • Parkinson's disease medications, such as levodopa or methyldopa
  • penicillamine
  • proton pump inhibitors, such as esomeprazole, lansoprazole, or omeprazole
  • quinapril
  • quinolone antibiotics, such as ciprofloxacin, norfloxacin, or ofloxacin
  • vitamin E.

Iron supplements may affect the results of some laboratory tests.

Note that this list is not all-inclusive and includes only common medications that may interact with ferrous sulfate. You should refer to the prescribing information for ferrous sulfate for a complete list of interactions.


Further information

Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use ferrous sulfate only for the indication prescribed.

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

Copyright 1996-2023 Revision date: August 30, 2023.