I am an adult taking oral iron (ferrous sulfate) and have left flank and posterior chest wall pain that worsens with the supplement; should I stop the iron and what alternative treatments for iron deficiency are recommended?

Should You Stop Iron and What Are the Alternatives?

Yes, you should stop the ferrous sulfate immediately—left flank and posterior chest wall pain worsening with iron supplementation is concerning for iron pill gastritis or other serious gastrointestinal pathology, and continuing the supplement risks progression to ischemic gastritis or gastric ulceration. 1

Immediate Action Required

Stop the ferrous sulfate now. Iron pill gastritis can occur in any patient receiving oral iron supplementation, particularly when there is underlying GI pathology, and can rapidly progress to severe gastritis with iron deposition in the gastric mucosa. 1 While this condition predominantly affects elderly patients, it has been documented in otherwise healthy adults in their 40s, and symptoms resolve rapidly with cessation of iron supplements. 1

Critical Warning Signs You're Experiencing

• Flank and posterior chest wall pain that worsens with iron intake suggests either:
  • Direct gastric mucosal injury radiating to the back
  • Potential gastric or duodenal ulceration
  • Rare but serious iron pill gastritis 1

The fact that your pain worsens specifically with the supplement establishes a clear temporal relationship that cannot be ignored.

Why This Happens

Oral iron supplementation, particularly ferrous sulfate, causes gastrointestinal side effects significantly more often than placebo (odds ratio 2.32) or intravenous iron (odds ratio 3.05). 2 Iron can precipitate in the GI tract causing direct mucosal damage, vomiting, dyspepsia, and in severe cases, acute gastritis with iron deposition on histology. 2, 1

Your Alternative Treatment Options

First-Line Alternative: Intravenous Iron

Intravenous iron is your best option given your intolerance to oral iron and the severity of your symptoms. 2

• IV iron produces a clinically meaningful hemoglobin response within one week, making it an excellent alternative to continued oral therapy. 2
• Modern formulations like ferric carboxymaltose (750-1000 mg) or ferric derisomaltose (1000 mg) can replenish your entire iron deficit in just 1-2 infusions. 2
• Rates of mild reactions are approximately 1:200 and major reactions approximately 1:200,000—substantially safer than continuing oral iron that's causing you pain. 2
• Cost is higher ($3,470-$3,896 for typical dosing vs. $0.30-$4.50 for oral iron), but this is justified given your intolerance. 2

Second-Line Alternative: Different Oral Formulation (Only After Symptom Resolution)

Only consider this if IV iron is not accessible and your symptoms completely resolve:

• Wait at least 2-4 weeks after stopping ferrous sulfate before attempting any oral iron to allow gastric healing. 1
• Ferric maltol (30 mg twice daily) may be better tolerated as GI side effects are comparable to placebo, though it's substantially more expensive (£47.60 vs £1.00 per 28 days). 2, 3
• Alternate-day dosing of any oral iron (if you retry) leads to significantly increased fractional absorption and may improve tolerance. 2

What NOT to Do

• Do not switch to ferrous fumarate or ferrous gluconate—there is no evidence these are better tolerated than ferrous sulfate. 2, 3
• Do not use modified-release preparations—they are "less suitable for prescribing" per the British National Formulary due to poor absorption. 2, 3
• Do not continue any oral iron while experiencing worsening pain—this risks progression to severe gastritis. 1

Evaluation You Need Before Restarting Any Iron

Before starting IV iron or considering any future oral iron:

• Rule out ongoing GI blood loss as a source of your iron deficiency, particularly given your new GI symptoms—this may require upper endoscopy. 2
• Check if you're taking proton pump inhibitors (omeprazole, etc.)—these significantly impair oral iron absorption and may have contributed to inadequate response. 4
• Assess for H. pylori infection if you develop persistent upper GI symptoms. 1

Expected Timeline with IV Iron

• Hemoglobin should increase by 1 g/dL within 2 weeks of IV iron administration. 2
• Complete iron store repletion occurs with 1-2 infusions of modern high-dose formulations. 2
• Follow-up hemoglobin check at 2-4 weeks to confirm response. 2

Common Pitfall to Avoid

Do not let cost concerns keep you on oral iron that's causing you harm. While IV iron is more expensive upfront, the risk of developing severe gastritis, gastric ulceration, or ongoing symptoms that prevent iron repletion far outweighs the cost difference. Your quality of life and safety must take priority. 2, 1