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SupplementScience

Indole-3-Carbinol (I3C) 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: Generally Safe

Potential Side Effects

  • GI symptoms — nausea, gas, bloating, and diarrhea (more common than with DIM due to stomach acid reactions)
  • Skin rash (uncommon)
  • Unsteadiness or balance issues at high doses (rare, reported in one trial)
  • Variable metabolite production — individual stomach pH differences create inconsistent conversion profiles

Drug & Supplement Interactions

  • CYP1A2 substrates — I3C strongly induces CYP1A2; may reduce levels of caffeine, theophylline, clozapine, and other 1A2 substrates
  • Estrogen-sensitive medications — modulates estrogen metabolism; consult oncologist if on hormonal therapies
  • Antacids and proton pump inhibitors — reduced stomach acid impairs I3C conversion to active metabolites; may reduce efficacy
  • Hormonal contraceptives — theoretical interaction with estrogen metabolism

Maximum Dose

Do not exceed: 400mg daily; higher doses may cause GI side effects and unpredictable metabolite formation

Full Indole-3-Carbinol (I3C) Guide

References

  1. (). Indole-3-carbinol for recurrent respiratory papillomatosis: long-term results. Journal of Voice.
  2. (). Placebo-controlled trial of indole-3-carbinol in the treatment of CIN. Gynecologic Oncology. DOI
  3. (). Single-dose and multiple-dose administration of indole-3-carbinol to women: pharmacokinetics based on 3,3'-diindolylmethane. Cancer Epidemiology, Biomarkers & Prevention. DOI