Updated: January 25, 2026
What Is Slow-Fe XR? Uses, Dosage, and What You Need to Know in 2026
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Peter Daggett
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Overview
Slow-Fe XR is an extended-release ferrous sulfate supplement designed to treat iron deficiency with fewer stomach side effects. Here's everything you need to know.
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Slow-Fe XR is one of the most widely recommended OTC iron supplements for patients who need to treat or prevent iron deficiency but struggle with the GI side effects of standard iron tablets. Here is a complete, up-to-date guide covering everything you need to know about Slow-Fe XR in 2026.
What Is Slow-Fe XR?
Slow-Fe XR is a brand-name extended-release iron supplement containing ferrous sulfate — the most commonly recommended form of oral iron. Each Slow-Fe XR tablet contains 142 mg of ferrous sulfate, which provides 45 mg of elemental iron. The "XR" or "slow-release" designation refers to its controlled-delivery hydrogel matrix system, which releases iron gradually over several hours rather than all at once.
Slow-Fe XR is classified as an OTC dietary supplement and is available without a prescription at pharmacies, grocery stores, and online retailers across the United States. It is the #1 doctor-recommended OTC iron-only supplement brand, according to the manufacturer.
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What Is Slow-Fe XR Used For?
Slow-Fe XR is used to treat or prevent iron deficiency and iron deficiency anemia. Specific indications include:
Iron deficiency anemia (IDA): The most common form of anemia worldwide. Causes include heavy menstrual bleeding, inadequate dietary iron, malabsorption (celiac disease, IBD), or chronic blood loss.
Prevention during pregnancy: Iron demands increase significantly during pregnancy. Slow-Fe XR is often recommended for pregnant women who experience nausea with standard prenatal iron.
Iron supplementation for at-risk groups: Women of reproductive age, frequent blood donors, vegans and vegetarians, and athletes engaged in endurance sports may have increased iron needs.
Support for chronic kidney disease (CKD) anemia: Oral iron supplements are often recommended alongside erythropoiesis-stimulating agents in CKD patients.
Slow-Fe XR Dosage: How Much Should You Take?
The standard recommended dosage for Slow-Fe XR is:
Adults: 1 tablet daily, or as directed by your doctor. Each tablet provides 45 mg of elemental iron.
Not intended for use in children under 12 years of age unless directed by a physician.
Duration: Do not use for more than 6 months unless directed by your doctor.
Your doctor may prescribe a different dosing schedule based on your ferritin and hemoglobin levels. Emerging research supports alternate-day dosing (every other day) as equally effective for some patients, with fewer GI side effects.
How to Take Slow-Fe XR Correctly
Swallow whole: Never crush, break, or chew the tablet. Doing so destroys the extended-release mechanism and may cause stomach irritation.
Best absorption: Take on an empty stomach (1 hour before or 2 hours after meals) for maximum absorption.
If stomach upset occurs: Take with a small amount of food — but not with milk, coffee, tea, or calcium-fortified foods, which reduce iron absorption.
Enhance absorption: Taking Slow-Fe XR with vitamin C (ascorbic acid) — such as a glass of orange juice — significantly enhances iron absorption.
Medication timing: Separate Slow-Fe XR from levothyroxine, tetracycline antibiotics, and fluoroquinolones by at least 2–4 hours to avoid reduced absorption of those medications.
Who Should NOT Take Slow-Fe XR?
People with hemochromatosis (iron overload disorder)
People with hemolytic anemia (destruction of red blood cells)
People with active peptic ulcer disease, ulcerative colitis, or regional enteritis
Patients who receive frequent blood transfusions
Children under 12 unless directed by a physician
Is Slow-Fe XR Safe During Pregnancy?
Iron supplementation during pregnancy is generally safe and often recommended. Slow-Fe XR's extended-release format can help pregnant women who struggle with the nausea caused by standard iron tablets or prenatal vitamins with high iron content. Consult your OBGYN before starting or changing any supplement regimen during pregnancy to determine the appropriate dose for your situation.
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The Bottom Line
Slow-Fe XR is a well-established, high-quality iron supplement that delivers 45 mg of elemental iron per day in a gentle, extended-release format. It's particularly well suited for patients who need long-term iron supplementation and want to minimize GI side effects. To understand exactly how Slow-Fe XR works in your body, see our guide on how Slow-Fe XR works.
Frequently Asked Questions
Slow-Fe XR is used to treat iron deficiency and iron deficiency anemia. It is commonly recommended for women of reproductive age with heavy periods, pregnant women, individuals with malabsorption conditions (IBD, celiac disease), frequent blood donors, and others at risk for iron deficiency.
Each Slow-Fe XR tablet contains 142 mg of ferrous sulfate, which provides 45 mg of elemental iron. Elemental iron is the actual amount of iron available for absorption — always check the elemental iron content when comparing iron supplements.
Iron is best absorbed on an empty stomach, but Slow-Fe XR can be taken with a small amount of food if stomach upset occurs. Avoid taking it with milk, dairy products, coffee, tea, or calcium-fortified foods, as these reduce iron absorption. Taking it with vitamin C (e.g., orange juice) enhances absorption.
Slow-Fe XR and Slow Fe both contain extended-release ferrous sulfate — they are essentially the same type of product. The 'XR' designation emphasizes the extended-release formulation. Both deliver 45 mg of elemental iron per tablet using a controlled-release matrix system.
Patients often notice increased energy levels within 2–4 weeks of starting iron supplementation. However, it typically takes 2–3 months of consistent use for hemoglobin to normalize and 6+ months for ferritin (iron stores) to fully replete. Follow your doctor's monitoring schedule with blood tests.
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