Slow-Release Iron

What is slow-release iron?

Slow-release iron (slow Fe) is a type of iron supplement that contains ferrous sulphate. It can release iron (Fe) from the ferrous sulphate into our bodies to combat iron deficiencies.1 The iron supplements can be in different forms as tablets, capsules, and liquids.

Purpose of slow-release iron

Slow-release iron can be used to treat iron deficiencies (like iron deficiency anaemia) given that iron is an essential mineral in our body as it is required for the production of red blood cells to carry oxygen around the body. Using slow-release iron can treat or prevent iron deficiencies, which are very common in anaemia or during pregnancy.2 

Benefits of slow-release iron

Slow-release iron is less harmful to the stomach whilst still providing a high potency. This is a great benefit since normal iron supplements can cause a lot of stomach problems; therefore, slow-release iron can reduce the common side effects.3

How to take slow-release iron?

When taking the slow-release iron, it is important to take the dosage advised by your doctor on an empty stomach and take it with a liquid (preferably water or orange juice as vitamin C can help the iron absorption) a few hours before meals. Do not lie down for at least 10 minutes after taking the medication. The slow-release tablets should be taken whole without chewing or crushing.2 

Forms of slow-release iron 

Slow-release iron has multiple different forms:

  • liquid-filled capsule. 
  • coated tablet.
  • capsule.
  • chewable tablet.
  • liquid.
  • long-acting capsule.
  • long-acting tablet.4


To treat anaemia, the usual recommended dose for adults is:

  • tablets: one 200mg tablet, taken 2 to 3 times a day.
  • liquid: 4ml, taken once or twice a day.5

To prevent anaemia, the usual recommended dose for adults is:

  • tablets: one 200mg tablet, taken once a day
  • liquid: 2.4ml to 4.8ml daily.5

It is crucial to discuss potential dosages with your doctor before beginning treatment as taking too much iron could lead to fatal poisoning. 


Patients with a medical history of intestinal problems (like ulcers or colitis) should inform their doctor as this medication can cause further problems. Also, if the iron supplement contains folic acid and you have a vitamin B12 deficiency, it is important to stay alert because folic acid may seem to improve the deficiency without being treated. Vitamin B12 deficiency can cause serious nerve problems like peripheral neuropathy symptoms. Do not take liquid forms of this supplement if you have diabetes, alcohol dependence, or liver disease as the liquid forms may contain sugar and alcohol. This medication may pass into breast milk, therefore consult your doctor before breastfeeding.2 

Slow-release iron interaction with other medications

Iron supplements may restrict the absorption of other drugs including bisphosphonates (e.g. alendronate), levodopa, penicillamine, quinolone antibiotics (e.g. ciprofloxacin, levofloxacin), thyroid medications (e.g. levothyroxine) and tetracycline antibiotics (e.g. doxycycline, minocycline).6

Side effects of slow-release iron

Side effects of slow-release iron include:5

  • constipation
  • diarrhoea 
  • stomach cramps
  • stomach upset 

If any of these symptoms persist, contact your doctor. 

Differences between quick- and slow-release iron

slow-release iron is less harmful to the stomach and therefore does not cause problems that are common when using iron supplements. As a result, slow-release Fe may have fewer side effects than normal iron supplements.3

Food sources of iron

Foods that contain high levels of iron include:7

  • liver
  • red meat
  • beans (like kidney beans, edamame beans, and chickpeas)
  • nuts
  • dried fruit
  • Soya bean flour 

How to increase the absorption of iron?

In order to increase iron absorption, it is recommended to take any iron supplements together with a source of vitamin C.8 This is because vitamin C increase both non-heme and heme absorption of iron. There is plenty of vitamin C sources including orange, fresh broccoli, fresh paper bell, citrus fruit, and strawberry.8 


Overall, slow-release iron is a supplement used to treat iron deficiencies that can occur due to different reasons, including pregnancies. Since iron deficiencies are quite common and the usual iron supplements have been found to irritate the stomach and sometimes cause intestinal problems, slow-release iron has been made to combat the potential stomach issues caused by other oral iron supplements. Additionally, taking any iron supplement alongside a glass of orange juice may improve the efficacy of the supplement as vitamin C has been shown to aid in iron absorption. 


  1. Slow release iron uses, Side Effects & Warnings [Internet]. [cited 2022Dec21]. Available from:   
  2. Lactation I of M (US) C on NSDP and. Iron nutrition during pregnancy [Internet]. National Academies Press (US); 1990 [cited 2022 Dec 21]. Available from: 
  3. Baird IM, Walters RL, Sutton DR. Absorption of slow-release iron and effects of ascorbic acid in normal subjects and after partial gastrectomy. BMJ [Internet]. 1974 Nov 30 [cited 2022 Dec 21];4(5943):505–8. Available from: 
  4. What is iron slow release: uses, warnings, interactions & faqs [Internet]. [cited 2022 Dec 20]. Available from:
  5. Ferrous sulfate: medicine for treating iron deficiency anaemia. [Internet]. 2019 [cited 2022 Oct 30]. Available from:
  6. Slow release iron oral: uses, side effects, interactions & pill images [Internet]. RxList. [cited 2022 Dec 21]. Available from: 
  7. Vitamins and minerals - Iron. [Internet]. 2017 [cited 2022 Oct 30]. Available from:
  8. 16168--how to increase iron in your diet(Patient handout view) [Internet]. [cited 2022 Dec 21]. Available from:,%2C%20cantaloupe%2C%20and%20fresh%20broccoli 
This content is purely informational and isn’t medical guidance. It shouldn’t replace professional medical counsel. Always consult your physician regarding treatment risks and benefits. See our editorial standards for more details.

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Patricia Barnuevo

Bachelor's degree, Biotechnology with Industrial Experience, The University of Manchester, England

"I am accustomed to working in diverse and multicultural environments, and thrive on feeding my intellectual curiosity. "

Experienced in both a dynamic, corporate laboratory as part of the R&D team, and in academic laboratory projects.
She is also an experienced medical Writer.

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