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Ferrous sulphate FAQs: 12 questions answered

woman taking iron tablets with glass of water

Ferrous sulphate is a form of iron supplement often used to replenish iron stores and support the unwelcome symptoms of an iron deficiency.

But how do ferrous sulphate tablets work? When can they help? And what is the best way to get the benefits from supplementary iron?

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  1. What's the difference between iron and ferrous sulphate?

Iron is a mineral. Its primary purpose is to make haemoglobin, a protein in red blood cells that transports oxygen around your body.

There are many sources and varieties of iron. They broadly fall into two main groups: ferric or ferrous. Ferrous sulphate is a form of ferrous iron. Others include ferrous fumarate and ferrous gluconate.

In its natural form, iron sulphate is a crystal. But due to being widely used as an iron supplement, you’ll usually find it in the form of tablets and droplets.

In short, ferrous sulphate is one kind of iron sulphate. You may also see it called ferrous sulfate or iron sulfate.

  1. What is ferrous sulphate used for?

It’s surprisingly common for people to be deficient in iron.

Ferrous sulphate is a dietary supplement that can boost your iron levels if you’re showing signs of a deficiency. As a result, it’s often used in the prevention and treatment of iron -deficiency anaemia.1

  1. Who should take ferrous sulphfate?

Most people get the iron they need from their diet. But taking an iron supplement, such as iron sulphate tablets, can be helpful if you’re finding it difficult to get the levels you need from food alone or are prone to low levels of iron.

If you’re iron deficient, you might feel tired, lightheaded, or weak.

Four groups that can be more at risk of an iron deficiency include:2

  • Teens: Particularly during growth spurts.
  • Females: Between the ages of 14 and 50, females tend to need more iron than males of the same age. This is particularly true for women who have heavy periods.
  • Pregnant women and new mums: Your iron needs increase when you’re pregnant and while breastfeeding. It can be difficult to meet this demand through diet alone.
  • Vegetarians or vegans: If you’re not able to eat iron-rich foods, such as meat and fish, it can lead to you not getting the recommended daily amount of the mineral.

Handpicked content: Why is iron so important for women?

  1. What does ferrous sulphate do in pregnancy?

The recommended daily iron intake increases to 27mg when you’re expecting a baby (compared to the standard 18mg for most adult women under 50).2

This is because the female body has to work overtime to supply blood and oxygen to the growing foetus. To manage this, the amount of blood in a woman’s body increases by nearly 50% during pregnancy.3

However, this increased demand means many pregnant women find themselves short of red blood cells. This increases their risk of anaemia.

If you’re pregnant and suspect you have an iron deficiency, the best course of action is to visit your doctor who can confirm this with a blood test. They may then suggest taking an iron sulphate supplement to build up your stores of this essential mineral.

  1. Is ferrous sulphate safe in pregnancy?

The simple answer is yes. But that doesn’t mean you should rush out to stock up on some kind of iron sulphate formula as soon as you get a positive pregnancy test.1

You only need to take ferrous sulphate in pregnancy under the advice of a medical practitioner and if you’re diagnosed with a deficiency.

This is because not every mum-to-be will need to take iron supplements. In reality, many women can get enough from food, combined with the extra iron in a multivitamin pregnancy supplement.

  1. Can you take folic acid and ferrous sulphate together?

Like iron, folic acid is an important nutrient for pregnant women. In fact, it’s recommended that women who are trying to conceive or are pregnant take folic acid until they’re 12 weeks pregnant.4

But can you combine these two mineral supplements? According to the NHS, you can safely take folic acid while also taking a ferrous sulphate supplement.4

  1. When should I take ferrous sulphate?

How you take iron supplements, like ferrous sulphate, can make them more effective. Here are a few general rules:

5 tips on how to take iron supplements

  • Your body may find iron sulphate easier to absorb when taken on an empty stomach
  • But if you get an upset stomach, you may prefer to take your dose with a meal
  • Taking ferrous sulphate with orange juice (or another vitamin C source) can increase the amount of iron your body absorbs8
  • Avoid taking it with tea, coffee, eggs, dairy products and soybean products. These are all shown to reduce the amount of iron that gets into your system9
  • Most importantly, always take iron supplements exactly as your doctor tells you to
  1. How much ferrous sulphate should I take?

Your ferrous sulphate dose depends on whether you’re taking it to prevent iron-deficiency anaemia or to treat it.

Typical adult ferrous sulphate dosage

  To prevent anaemia To treat anaemia
Iron sulphate tablets Dose: one 200mg tablet Dose: one 200mg tablet
Iron sulphate drops Dose: 2.4ml - 4.8ml Dose: 4ml
  Frequency: once a day Frequency: once/twice a day


  1. How quickly does ferrous sulphate work?

Although you won’t feel the benefits of taking ferrous sulphate instantly, it won’t take too long to show its effects. In most cases, people begin to see signs of improvement in iron deficiency symptoms after around 1 week. The full effects are likely to be felt within 4 weeks of taking the supplement.1

  1. How long should I take ferrous sulphate?

You can safely take ferrous sulphate for as long as you need to. How long you need to take it will depend on how low your iron levels are.

  • If you’re taking ferrous sulphate to prevent anaemia, you may need to take it for as long as you’re at risk of iron deficiency.1
  • For those taking ferrous sulphate to help resolve iron deficiency anaemia, expect it to take 3-6 months to build up your iron stores.1
  1. Does ferrous sulfate have side effects?

Some people may experience unwanted side effects from taking ferrous sulphate.

10 common ferrous sulfate side effects

  • Constipation
  • Diarrhoea
  • Nausea or vomiting
  • Stomach pain
  • Heartburn
  • Loss of appetite
  • Constipation
  • Diarrhoea
  • Black (or dark) poo
  • Black stained teeth (from drops

For most people, these complaints will be mild and there are often things you can do to help reduce or avoid them. For example, taking iron just after eating can help reduce any stomach troubles and boosting the fibre in your diet can ease constipation.

However, if you take too much ferrous sulphate these side effects can be amplified and more serious. So always make sure to keep to your recommended ferrous sulphate dose.


  • For optimal absorption, you’re best to take ferrous sulphate on an empty stomach
  • Taking it with orange juice can make it more effective, whereas tea can reduce absorption
  • The right ferrous sulphate dose for you will depend on how low your iron levels are
  • You will probably start to see the effects of taking the supplement after around one week
  • You should continue to take ferrous sulphate until you’re no longer at risk of iron-deficiency anaemia
  • Some side effects include sickness, diarrhoea, black poo and constipation.
  1. Does ferrous sulphate cause constipation?

As discussed above, constipation can be an unwanted side effect of taking a ferrous sulphate supplement.

Unabsorbed iron in your body can feed pathogenic bacteria in your gut, which causes changes in your microbiome and can lead to effects like constipation.⁵

Generally improving your gut health could help to reduce this, though it likely won’t stop it altogether. Drink plenty of water and see if you can include some gut-friendly bacteria into your diet with high-fibre and fermented foods.

If you’re struggling with constipation while taking ferrous sulphate, try changing up the time you take it. It’s recommended you take it on an empty stomach, but if your gut is particularly sensitive, it might help to take your iron sulphate supplement directly after a meal.

You might also find that a stool softener provides some relief.

Handpicked content: 8 easy ways to prevent constipation

Conclusion: Can taking ferrous sulphate help an iron deficiency?

Ferrous sulphate is a type of iron that your body absorbs relatively easily. It can be used to help to restore iron levels in people suffering from a deficiency.

Groups of people who are more susceptible to iron-deficiency anaemia (including menstruating women, pregnant females and adolescents) are likely to benefit most from ferrous sulphate supplements.

However, for most other people, it’s possible to get the iron you need by including a variety of iron-rich food sources in your diet.

The advice in this article is for information only and should not replace medical care. Please check with your GP or healthcare professional before trying any supplements, treatments or remedies. Food supplements must not be used as a substitute for a varied and balanced diet and a healthy lifestyle.

Before taking any supplements or minerals, it’s best to make sure you’re getting all the nutrients through your diet first.

Food supplements must not be used as a substitute for a varied and balanced diet and a healthy lifestyle.

Last updated: 9 September 2022

Last updated: 15 April 2021


  1. https://www.nhs.uk/medicines/ferrous-sulfate/
  1. https://www.whattoexpect.com/pregnancy/diet/iron-during-pregnancy/
  2. https://www.tommys.org/pregnancy-information/im-pregnant/nutrition-in-pregnancy/iron-pregnancy
  3. https://www.nhs.uk/medicines/folic-acid/
  4.   https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7400826/

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