What Are the Side Effects of Taking Iron Supplements?

If you're thinking about taking iron supplements, it's important to know that they can come with a variety of side effects.

From mild tummy troubles to more serious concerns like iron overdose, this article aims to give you the full picture on what to expect when supplementing with iron.

What Are the Side Effects of Taking Iron Supplements

Do Iron Supplements Have Negative Side Effects?

Yes, traditional iron supplements often come with a range of negative side effects. These can include gastrointestinal issues like constipation and nausea, as well as less common problems like metallic taste, skin reactions, and allergic reactions.

Why do Most Iron Supplements Cause Gastro-Intestinal (GI) Side Effects?

The gastrointestinal system is often the first to show signs when you begin taking iron supplements. Common symptoms include constipation, nausea, diarrhea, and upset stomach. These side effects arise because iron ions can be irritating to the gastrointestinal tract lining.

In more scientific terms, the iron ions can interact with various enzymes and substances in the digestive system, leading to a disruption of normal gut activity. For example, increased iron in the gut can alter the osmotic balance, leading to diarrhea or constipation depending on individual reactions and dosage. Iron ions can also trigger the release of serotonin in the gut, which can cause feelings of nausea.

These symptoms are generally mild and may subside as your body gets used to the supplement. However, they can be uncomfortable and inconvenient, particularly if you're not prepared for them. In some cases, they simply do not recede either.

Other Common Side Effects 

Here are the common side effects of conventional iron supplementation. 

  • Constipation
  • Nausea
  • Diarrhea
  • Upset stomach
  • Dark stools
  • Metallic taste
  • Skin reactions
  • Allergic reactions
  • Fatigue
  • Headache
  • Dizziness


Constipation is a frequent complaint among those taking iron supplements.

Iron can reduce the activity of smooth muscle cells in the gastrointestinal tract, slowing down bowel movements. The issue stems from iron's interaction with the gut microbiome and its effect on intestinal motility. In some cases, constipation can become severe enough to require medical intervention. Drinking plenty of water and increasing dietary fibre can help alleviate this symptom.


Another common side effect is nausea, often occurring shortly after taking the supplement.

The iron ions interact with serotonin receptors in the gut, which can trigger nausea and vomiting reflexes. Taking the supplement with a small amount of food can often mitigate this effect, but if nausea persists, it may be necessary to consult a healthcare professional.


Diarrhea is a less common but still possible side effect of iron supplementation.

The iron ions can alter the osmotic balance in the gut, drawing water into the intestinal lumen and causing loose stools. This is particularly likely when high doses of iron are ingested. If diarrhea is persistent or severe, medical advice should be sought.

Upset Stomach 

Some people experience a general sense of stomach discomfort or upset when taking iron supplements. This can manifest as cramps, bloating, or a feeling of fullness. The cause is often the same as that of nausea—interaction with serotonin receptors in the gut. Taking the supplement with food or switching to a slow-release formulation can often alleviate these symptoms.

These gastrointestinal side effects are among the most commonly reported and can often be managed with simple lifestyle changes. However, persistent or severe symptoms should be evaluated by a healthcare professional.

Dark Stools

Another commonly observed side effect of taking iron supplements is darkened stools. This change in colour is generally not a cause for alarm and is actually a direct result of the iron being processed by your body.

When you ingest iron supplements, the iron combines with gastric acids in the stomach. This mixture is then passed through the digestive system, where it may react with other compounds and enzymes. These reactions can result in the formation of a dark, often blackish, insoluble iron compound called ferric sulfide. This compound is what gives the stool its darkened colour.

While dark stools might be unsettling if you're not expecting them, understanding that this is a common reaction to iron supplements can be reassuring. Nonetheless, if the darkened stool is accompanied by other symptoms or persists for an extended period, consultation with a healthcare professional is advisable.

Metallic Taste

One lesser-known but still common side effect of taking iron supplements is experiencing a metallic taste in the mouth. This occurs due to the presence of iron ions interacting with taste receptors on the tongue. These receptors are sensitive to various minerals and compounds, and iron happens to be one that can cause a noticeable change in taste perception.

The metallic taste is generally short-lived and tends to dissipate as the body processes the iron. While it's not harmful, many people find it off-putting or unpleasant. If you find the metallic taste particularly bothersome, some find relief by taking the supplement with citrus juice, which not only masks the taste but can also aid in iron absorption.

Skin Reactions

Some individuals may experience skin reactions when taking iron supplements. These can manifest as rashes, itchiness, or even more severe allergic reactions in rare cases. The exact mechanism behind these skin reactions is not entirely understood but is likely related to an immune response.

The body's immune system can sometimes identify the iron ions as foreign bodies, triggering an allergic response. This could lead to the release of histamines, substances that cause the allergic symptoms such as rashes and itchiness. If you experience any severe skin reactions, it's crucial to discontinue the supplement and seek immediate medical advice.

Allergic Reactions

Though relatively rare, some people may experience allergic reactions to iron supplements. Symptoms can include hives, difficulty breathing, and swelling of the face, lips, tongue, or throat. These reactions occur when the immune system mistakenly identifies the iron supplement as a harmful substance and releases chemicals like histamines to fight it off.

An allergic reaction to an iron supplement is a medical emergency requiring immediate attention. If you suspect you're experiencing an allergic reaction, discontinue use of the supplement and seek emergency medical care. It's crucial to identify this allergic sensitivity as early as possible to avoid more severe complications.


Ironically, some people report feeling fatigued or unusually tired when they start taking iron supplements. This seems counterintuitive, given that one of the primary reasons for taking iron is to combat fatigue associated with conditions like anaemia.

The reason for this paradoxical effect isn't entirely clear but may be related to the body's adjustment period to increased iron levels. Iron plays a complex role in the body's metabolic pathways, and introducing additional iron might temporarily disrupt these processes before a new equilibrium is reached. If you experience persistent fatigue while taking iron supplements, it's important to consult a healthcare professional for a comprehensive evaluation.


Headaches are another side effect that some individuals experience when taking iron supplements. The exact mechanism behind this is not fully understood, but it is hypothesized that it may be related to changes in blood pressure or alterations in blood flow. Iron plays a role in the formation of haemoglobin, the molecule in red blood cells that carries oxygen. Changes in haemoglobin levels could potentially affect blood flow to the brain, leading to headaches.

It's also possible that headaches are a result of the body adjusting to increased iron levels, especially if supplementation is started at a high dosage. If headaches are persistent or severe, reducing the dosage under medical supervision or discontinuing the supplement may be necessary. Consulting a healthcare professional for persistent symptoms is advisable.


Dizziness is a less common but noteworthy side effect of iron supplementation. Similar to headaches, the cause of dizziness is not entirely clear but may be linked to changes in blood pressure or blood oxygen levels. As iron supplements increase haemoglobin levels, this could temporarily alter the body's physiological equilibrium, leading to sensations of dizziness or instability.

If you experience dizziness, it's crucial to exercise caution, especially when driving or operating heavy machinery. As with other side effects, persistent or severe dizziness should be evaluated by a healthcare professional to rule out other potential causes and to adjust the iron supplementation regimen if needed.

Is There an Iron Supplement with No Side Effects?

If you're tired of dealing with the side effects that come with most iron supplements, Nano Iron is the solution you've been looking for. Unlike traditional iron supplements, Nano Iron eradicates almost all known side effects for most users.

This breakthrough is possible because of Nano Iron's unique formulation, which allows for direct absorption into cells, bypassing the digestive system entirely. This means you get all the benefits of iron without the usual downsides.

Learn More

Do Side Effects of Iron Supplements Go Away?

Contrary to common belief, some side effects like constipation, nausea, and heartburn may not necessarily go away over time and can persist during the course of iron supplementation.

While some individuals find that their bodies adjust to the iron supplement, leading to a reduction in side effects, this is not the case for everyone. Gastrointestinal issues such as constipation and nausea can persist for as long as you are taking the supplement. This is because the iron ions in the supplement interact with enzymes and other substances in the gastrointestinal tract, leading to continued discomfort.

In some cases, adjusting the type or dosage of iron supplement may alleviate some of these persistent side effects. For example, some individuals find relief by switching to a slow-release or lower-dose formulation. However, these modifications should only be made under medical supervision.

Which Iron Supplement is Better Tolerated

If you're looking for an iron supplement that's easy on the body, Nano Iron is your best bet. Unlike traditional iron supplements, which can cause a range of uncomfortable symptoms, Nano Iron is formulated to eliminate nearly all known side effects.

Nano Iron consists of ultra-small particles, sized between 0.5 and 7 nanometers, suspended in purified water. This small size allows the iron to be directly absorbed into cells, bypassing the digestive system entirely. This unique feature is why Nano Iron doesn't cause the usual gastrointestinal issues associated with other iron supplements.

Another advantage of Nano Iron is its 100% bioavailability, meaning the body can absorb and use all the iron provided. This is in contrast to traditional iron supplements, where absorption rates can be as low as 10 to 15%. As for dosage, Nano Iron offers flexibility. Even in severe cases of iron deficiency, high doses can be taken without the risk of overdose or side effects.

FAQS on Iron Side Effects

Q: Can iron supplements affect my teeth?
A: Yes, some people have reported that liquid iron supplements can stain teeth. This is generally more common with ferrous sulfate solutions. The staining can usually be removed by a dentist, but it's advisable to consult healthcare professionals for alternatives if this side effect is a concern.

Q: Do iron supplements interfere with other medications I might be taking?
A: Iron supplements can interact with certain medications, including some types of antibiotics and antacids. This can either make your medication less effective or increase its side effects. Always consult your healthcare provider when adding an iron supplement to your regimen if you're already on other medications.

Q: Can iron supplements affect my menstrual cycle?
A: There is limited evidence to suggest that iron supplements have a direct impact on the menstrual cycle. However, iron supplementation is often recommended for menstruating individuals to replenish lost iron, especially if heavy periods lead to iron-deficiency anaemia.

Q: Are there side effects related to long-term storage of iron supplements?
A: Iron supplements, like any medication, have a shelf life. Using expired supplements can lead to reduced effectiveness and a potential increase in side effects, such as gastrointestinal discomfort.

Q: Can iron supplements cause weight gain?
A: There's no scientific evidence to suggest that iron supplements cause weight gain. However, if you're iron-deficient, proper supplementation may improve your energy levels, potentially leading to increased physical activity and muscle gain over time.

Q: Are the side effects of iron supplements different for children and adults?
A: Children are more sensitive to iron and are at a higher risk for iron overdose, which can be fatal in severe cases. While some side effects like constipation and nausea might be common across age groups, the severity and risk factors can differ. Always consult a paediatrician before giving iron supplements to children.

Q: Can iron supplements cause joint pain?
A: Joint pain is not a commonly reported side effect of iron supplements. However, excessive iron storage, known as hemochromatosis, can lead to joint pain among other symptoms. If you experience unexplained joint pain, consult your healthcare provider.

Q: Is it possible for iron supplements to cause a rash?
A: While rare, some people may experience skin rashes as an allergic reaction to iron supplements. If you notice a rash after starting an iron supplement, discontinue use and consult a healthcare professional.

Q: Can iron supplements impact my mood?
A: Iron plays a role in producing neurotransmitters like serotonin and dopamine. While not a direct side effect of the supplement, correcting an iron deficiency can improve mood in some individuals.

Q: Do iron supplements have an effect on hair and nails?
A: Iron deficiency is linked to hair loss and brittle nails. While not a side effect, proper iron supplementation may lead to improvements in hair and nail health for those who are deficient.