Do Iron Supplements Cause Black Stools & is There One Which Doesn't?

Many first-time users of iron get shock to notice their stools turning dark, completely black, or with a greenish tinge while supplementing.

Black stools, are also known as melena, from the Greek word "melas," meaning "black."

Understandably, many panic at the sight, fearing gastrointestinal bleeding or other health issues might be causing it.

The good news is black poop isn't usually problematic, but a common side-effect of ingesting certain types of iron.

But it is worth understanding the science behind this, so you can put your mind at rest, as well as when its recommended to consult a doctor.

I'll also explain how Nano Iron can solve this problem entirely, returning your stools to their normal colour.

Is there an iron supplement that doesn't cause black stools

Why Do Iron Supplements Turn Your Stools Black?

Put simply, iron supplements make your stools black because of the unabsorbed iron in the gut forming complexes with other compounds in the digestive tract.

Iron supplements generally contain iron in ionic forms, such as ferrous sulfate, ferrous gluconate, or ferrous fumarate, which the body absorbs directly. However, the body can only absorb a certain amount of iron at a time, and any excess remains in the digestive tract.

The excess iron in the gut can react with other compounds produced by gut bacteria, forming non-absorbed iron complexes. These complexes can impart a black colour to the stool, making it appear dark or black.

While stool colour isn't harmful, what's more concerning about most iron supplements are their other side effects such as nausea, heartburn and constipation. These side effects can be significant enough to cause some individuals to stop taking their iron supplements, which can lead to further health problems related to iron deficiency.

Does Black Stool Mean Too Much Iron?

No, black stool does not necessarily mean too much iron; it often occurs when the body processes iron supplements.

Which Common Iron Supplements Cause Black Poo?

Ferrous sulfate is one of the most widely used iron supplements and also one of the most common causes of black stool. It provides iron in the ferrous state (Fe2+), which is a form that is readily absorbed.

Ferrous gluconate is another commonly used iron supplement that can cause darkened stools. It combines ferrous iron with gluconic acid for increased bioavailability.

Other types of iron supplements that may cause black stool include:

  • Ferrous fumarate - Provides ferrous iron bound to fumaric acid.
  • Ferrous asparto glycinate - Chelated ferrous iron.
  • Carbonyl iron - Pure elemental iron in the form of microbeads.
  • Iron polysaccharide complex - Iron bound with a polysaccharide.
  • Heme iron polypeptides - Iron derived from hemoglobin.
  • Ferrous bisglycinate - Ferrous iron chelated with glycine.

The level of elemental or absorbable iron varies amongst these different supplements. Generally the more elemental iron a supplement contains, the more likely it may cause black stool as a temporary side effect. The degree of darkening can also depend on the individual and dosage consumed.

How to Identify Black Stools from Iron Supplementation

The following information may help you identify black stools from iron supplements:

  • Black stools are typically shiny and black in colour, almost like tar or dark chocolate. They may be sticky and have a foul smell.
  • The colour change is usually accompanied by a change in consistency and odour of the stool.
  • Black stools caused by iron supplements can occur within a few days of starting the supplement, and may persist for as long as the supplement is taken.
  • If you notice any other symptoms you should contact your healthcare provider as these may be signs of a more serious issue.

Should You Stop Iron Supplements if Poop is Black?

Unless there are other troubling symptoms present, like bloody stool, continuing diarrhea, severe pain, or vomiting, the black stool itself is not dangerous.

However, you should notify your doctor to discuss the timing and dosage of the iron if the black stool persists or worsens.

Your doctor may recommend adjusting the iron supplement type or dosage to reduce staining while still treating iron deficiency. Typically there is no need to stop the iron supplements unless advised by your doctor, as maintaining adequate iron levels is important. Be sure to also report any constipation or diarrhea that results from iron supplements, as the dosage may need modifying to improve digestion.

When to See a Doctor About Black Stools

You should see a doctor about black stools in the following situations:

  1. If the black stool is accompanied by symptoms such as abdominal pain, nausea, vomiting (especially if vomit looks like coffee grounds), fatigue, or weakness. These could be signs of gastrointestinal bleeding or other serious conditions.

  2. If you have not been taking iron supplements or consuming foods known to darken stool. In such cases, black stool could indicate bleeding in the upper gastrointestinal tract.

  3. If you experience a sudden change in bowel habits or the appearance of your stool that persists for more than a couple of days.

  4. If you're experiencing black stools along with signs such as pale skin, shortness of breath, dizziness, or irregular heartbeat.

  5. If there are other changes in the stool besides colour, such as consistency (if it becomes tar-like and sticky), which can also indicate bleeding.

In any case, it's important to consult with a healthcare professional to determine the cause of black stools and to receive appropriate treatment or dietary advice. Early consultation can help prevent potential complications and ensure that any underlying conditions are treated properly.

"Does Black Poop Mean My Iron Tablets are Working?"

While black poop can signify that iron from the supplement is getting through the gastrointestinal system, it does not necessarily mean the body is absorbing a sufficient amount of the iron. Stools can become black even if very little iron is being utilised by the body.

The only way to know if your iron tablets are effectively raising iron levels is through follow-up blood work and monitoring symptoms of deficiency with the help of your health care professional. Work with your healthcare provider to ensure your iron supplement routine is optimal for your needs.

Nano Iron: A Supplement that Won't Change Stool Colour

Made from pure elemental iron at an incredibly tiny size, Nano Iron is a tasteless, odourless liquid that is entirely gentle on the stomach, and won't cause any change in stool colour.

The tiny particles begin to be absorbed straight through the soft tissues of your mouth and throat, meaning less iron ends up in your gastrointestinal tract. As well as keeping your stools the right colour, this means a completely gentle experience for your stomach, with no diarrhea, hearburn or nausea.


Should I stop taking iron supplements if my stool is black?

If your stool turns black after taking iron supplements, it is generally not necessary to stop taking the supplement. This is a common side effect and does not necessarily indicate a problem. However, if you are concerned or experience other symptoms such as abdominal pain, nausea, vomiting, etc., you should talk to your healthcare provider. You should also consider supplements such as nano iron which are less likely to negatively impact your microbiome.

How long does poop stay black after iron tablets? 

Black stool caused by iron tablets can persist as long as the supplement is taken. However, if you stop taking the supplement, your stool should return to its normal color within a few days. If your stool remains black after stopping the supplement, or if you experience other concerning symptoms, you should talk to your healthcare provider.