Which Iron Supplement Does Not Give Constipation? A Guide to Gentle Formulas

January 3, 2026 •

3 min read

Approximately 18-20% of patients experience constipation from standard ferrous sulfate iron, but there are gentler alternatives available. This guide explores which iron supplement does not give constipation, focusing on formulations designed to be easier on the stomach and reduce unpleasant side effects.

Quick Summary

Explore alternative iron supplements, including chelated forms and polysaccharide iron complexes, known for fewer gastrointestinal side effects. Learn strategies to improve tolerance and absorption for effective iron supplementation.

Key Points

Ferrous Bisglycinate: This chelated form is generally the most gentle and highly absorbable iron supplement, causing minimal gastrointestinal distress.
Less Constipation-Inducing Forms: Polysaccharide iron complex and iron polymaltose are less likely to cause constipation and other GI side effects than traditional ferrous salts.
Mechanism of Constipation: The primary reason for constipation is unabsorbed iron in the digestive tract irritating the gut; highly absorbable forms minimize this issue.
Dosing and Schedule Adjustments: Starting with a low dose, splitting the dose, or using an intermittent schedule can help reduce the incidence of iron-induced constipation.
Supportive Lifestyle Measures: Staying hydrated, increasing dietary fiber, and regular exercise are effective non-supplement strategies for managing and preventing constipation.
Consult a Professional: Always speak with a healthcare provider before starting iron supplementation to determine the correct dose and best form for your needs.

Understanding Why Iron Causes Constipation

Iron is an essential mineral vital for producing hemoglobin, which carries oxygen in red blood cells throughout the body. When supplementing for iron deficiency, a significant portion of orally ingested iron, particularly from common ferrous salts like ferrous sulfate, is not fully absorbed. This unabsorbed iron in the digestive tract can cause irritation, alter gut bacteria, and slow intestinal movement, leading to constipation, nausea, cramps, and bloating. Choosing a different type of iron supplement can help minimize these side effects.

The Best Iron Supplements That Don't Cause Constipation

Certain iron formulations are known for being gentler on the digestive system. These include:

Ferrous Bisglycinate

Often recommended for its stomach-friendly properties, ferrous bisglycinate is a chelated form where iron is bound to two glycine molecules. This makes it highly absorbable and stable, reducing gut irritation. Studies indicate it causes fewer gastrointestinal issues, including constipation, compared to traditional ferrous salts and is suitable for sensitive stomachs.

Polysaccharide Iron Complex

This large, non-ionic form of iron is less likely to break down in the stomach, resulting in less unabsorbed iron in the lower digestive tract and fewer side effects like constipation and nausea. Clinical trials have shown products with polysaccharide iron complex to cause fewer GI side effects than ferrous sulfate.

Heme Iron Polypeptide

Derived from animal sources, heme iron is highly bioavailable and absorbed differently than non-heme iron. This allows for effective lower doses, reducing unabsorbed iron and the likelihood of constipation. It can be a gentle option with some studies showing higher absorption than non-heme iron salts.

Slow-Release Formulations

Slow-release or enteric-coated capsules can gradually release iron, potentially reducing gut irritation. While this improves tolerability, it might slightly lower overall absorption compared to immediate-release forms.

Comparison of Common Iron Supplements


Iron Form	Bioavailability	Gastrointestinal Side Effects	Common Examples	Cost
Ferrous Sulfate	Good	High risk of constipation, nausea, cramps	Nature Made Iron, Iberet Folic	Low
Ferrous Bisglycinate	Very High	Low risk; gentle on the stomach	Thorne Iron Bisglycinate, Solgar Gentle Iron	Moderate to High
Polysaccharide Iron	Good	Low risk; fewer side effects reported	Maltofer, Ferricure	Moderate
Heme Iron Polypeptide	Very High	Low risk; highly absorbable at smaller doses	Proferrin	High

Strategies to Minimize Iron-Induced Constipation

If you experience digestive issues, consider these strategies:

Start with a lower dose and increase gradually.
Take with Vitamin C to enhance absorption.
Stay well-hydrated.
Increase dietary fiber.
Exercise regularly.
Consider taking your supplement every other day.

Who Should Consider a Gentler Iron Supplement?

Individuals who may benefit from a gentler iron formulation include pregnant women, those with IBS, people with sensitive stomachs, and patients needing high doses.

Important Considerations Before Starting Iron Supplements

Always consult a healthcare professional before starting iron supplementation to confirm deficiency, determine dosage, discuss interactions, and find the best form. Over-supplementing can be dangerous. More information is available from resources like the National Institutes of Health.

Conclusion: Finding the Right Iron Supplement for You

Choosing the right iron supplement is key to avoiding constipation. Gentler, more absorbable options like ferrous bisglycinate or polysaccharide iron complex are often effective alternatives to traditional ferrous salts. Combining the right supplement with lifestyle adjustments like hydration, fiber, and exercise can help manage iron deficiency without discomfort.

Frequently Asked Questions

Constipation often occurs with iron supplements because unabsorbed iron in the gut can irritate the intestinal lining, which slows down intestinal transit and affects the gut microbiome.

Yes, ferrous bisglycinate is a chelated form known to be much gentler on the stomach with fewer reported gastrointestinal side effects, including constipation, compared to ferrous sulfate.

Good alternatives include polysaccharide iron complex, iron polymaltose, and heme iron polypeptide, as they are associated with better absorption and fewer digestive issues.

Taking iron with a light meal can reduce nausea and stomach upset, although it might slightly reduce absorption. Taking it with vitamin C, however, can enhance absorption and help you tolerate lower doses.

Increasing fiber intake from fruits, vegetables, and whole grains, along with drinking plenty of fluids, is recommended to help soften stools and promote regular bowel movements while on iron therapy.

If digestive issues persist, a healthcare provider might suggest adjusting the dose, recommending a stool softener, or exploring other options like intravenous (IV) iron infusions.

People with sensitive digestive systems, those who take high doses, pregnant women, and individuals with underlying bowel conditions like IBS are more prone to iron-induced constipation.