Iron supplements (oral)

Easy-to-read medicine information about iron supplements – what are they, how to take iron supplements safely and possible side effects.

Type of medicine Also called
  • Iron supplements
  • Ferrous sulfate
  • Ferrous fumarate
  • Ferrous gluconate
  • Ferodan®
  • Ferro-Liquid®
  • Ferro-Tab®
  • Ferrograd®
  • Ferro-Gradumet®

What are iron supplements?

  • Iron supplements are used to treat or prevent low blood levels of iron (iron deficiency).
  • They increase the amount of iron stores in your body.
  • Most people have an adequate iron intake with a healthy, balanced diet. However, sometimes people may require iron supplementation such as:
    • pregnant women or teenage girls, who have higher iron requirements
    • those who do not absorb iron normally such as people with renal failure or gut problems (malabsorption).
    • anyone with ongoing or excessive blood loss eg, women with heavy periods (menorrhagia)
  • If you have low iron levels, your doctor may prescribe, or your pharmacist may recommend iron supplements, to be taken by mouth (called oral iron supplements). 
  • In certain circumstances if oral iron supplements are not effective (cannot be absorbed from the gut) or if it cannot be tolerated, then iron supplements can be given by injection.

Types of iron supplements

  • There are a variety of different salt forms of iron available in New Zealand such as ferrous sulfate and ferrous fumarate (where ferrous is the Latin word to describe iron).
  • Each of these ferrous salts has a different amount of actual iron (called elemental iron). 
  • There is no particular advantage of one ferrous salt type over another, provided you receive adequate elemental iron, so choice of medicine is dependent on the risk of side effects and cost.
  • For example: 
    • Each 200 milligram tablet of Ferro-Tab® (which contains ferrous fumarate) has 65 milligrams of elemental iron.
    • Each 325 milligram tablet of Ferro-gradumet® or Ferrograd® (which contains ferrous sulfate, dried) has 105 milligrams of elemental iron.  
    • Each 5 milliliters (5 mL) of Ferodan® liquid or Ferro-Liquid® (which contains ferrous sulfate) has 30 mg of elemental iron.


  • The dose needed will vary depending on whether the iron supplement is used to treat or prevent low iron levels.  
  • It is usually prescribed between 1 to 3 doses a day.
  • Always take your iron supplement exactly as your doctor has told you. The pharmacy label on your medicine will tell you how much to take, how often to take it and any special instructions. Talk to your doctor or pharmacist if you have any questions regarding your medication or dosage.

How to take iron supplements

  • Iron supplements are best taken on an empty stomach (usually if taken 1 hour before or 2 hours after meals). If stomach upset occurs, you may take this medication with food.
  • Avoid taking antacids, dairy products, tea, or coffee within 2 hours before or after this medication because they will decrease its effectiveness.
  • Take tablets or capsules with a full glass of water. Do not lie down for 10 minutes after taking your tablet or capsule dose.
  • Swallow extended-release tablets whole. Do not crush or chew extended-release tablets, as this will release all of the medication at once, increasing the risk of side effects. 
  • If you are taking the liquid form for adults, carefully measure the dose using a special measuring device or spoon. Do not use a household spoon because you may not get the correct dose. Mix the dose in a glass of water or juice, and drink the mixture through a straw to prevent staining the teeth.
  • It is not harmful if you miss a dose of your iron supplement. If you miss a dose, just take your next dose at the right time. Do not take double the dose.

Possible side effects

Like all medicines, iron supplements can cause unwanted side effects, although not everyone gets them. Often unwanted effects improve as your body gets used to the new medicine.  

Side effects What should I do?
  • Dark or black-coloured stools 
  • Iron supplements can make your stools look darker in colour
  • This is completely harmless
  • Feeling sick (nausea)
  • Try taking your iron supplement with food
  • Tell your doctor or pharmacist if troublesome
  • Constipation
  • This usually settles as your body gets used to the medication
  • Tell your doctor or pharmacist if troublesome — you may need a suitable laxative, which you need to take on a regular basis
  • You also need to eat more fruit such as kiwifruit, vegetables, brown bread, bran based breakfast cereals and drink plenty of water
  • Diarrhoea or loose stool 
  • This usually settles as your body gets used to the medication
  • Tell your doctor or pharmacist if troublesome 


  • Some multivitamin and mineral products may contain iron salts, so check with your doctor or pharmacist, if you are taking these.
  • Some medicines available without a prescription may react with iron supplements such as antacids (e.g. Mylanta) or supplements containing aluminium (e.g. Alu-Tab®), calcium (e.g. Osteo®), magnesium (e.g. Chelated Magnesium®) or zinc (e.g. Zincaps®). Do not take these within two hours of iron supplements. Check with your pharmacist regarding any interactions.

Learn more

The following links provide further information on iron supplements. Be aware that websites from other countries may contain information that differs from New Zealand recommendations.

New Zealand Formulary Patient Information: iron supplements

Medsafe consumer information: Ferodan oral solution

Patient Info, UK: Iron supplements

Credits: Sandra Ponen, Pharmacist. Reviewed By: Dr J Bycroft. Health Navigator NZ Last reviewed: 21 Oct 2015