Skip to main content
SupplementScience

Iron Side Effects & Safety

This content is for informational purposes only and does not constitute medical advice. Consult your healthcare provider before starting any supplement. Full disclaimer

Safety Profile

Overall safety rating: Caution Needed

Potential Side Effects

  • Constipation (very common with ferrous sulfate)
  • Nausea and stomach cramps
  • Dark/black stools (harmless but expected)
  • Diarrhea (less common)
  • Iron overload risk with chronic excessive supplementation — can cause organ damage

Drug & Supplement Interactions

  • Reduces absorption of levothyroxine, tetracyclines, quinolones, bisphosphonates — separate by 2-4 hours
  • Calcium, zinc, and magnesium compete for absorption — take at different times
  • Vitamin C enhances iron absorption by 2-3x — beneficial co-supplement
  • Proton pump inhibitors and antacids reduce iron absorption
  • Tannins in tea and coffee reduce iron absorption by up to 60%

Maximum Dose

Do not exceed: 45mg/day elemental iron for adults (NIH UL); therapeutic doses up to 65mg under medical supervision

Full Iron Guide

References

  1. (). Effect of iron supplementation on fatigue in nonanemic menstruating women with low ferritin: a randomized controlled trial. CMAJ. DOI
  2. (). Iron absorption from oral iron supplements given on consecutive versus alternate days and as single morning doses versus twice-daily split doses. The Lancet Haematology. DOI
  3. (). Iron deficiency. The Lancet. DOI