Indole-3-Carbinol (I3C) — answers to I3C

Why it’s used

Taken by some with an interest in hormone metabolism, particularly estrogen breakdown, and marketed toward general cellular health support.

What the evidence says

Human clinical evidence is limited and mixed. Some small trials have looked at I3C's effect on estrogen metabolite ratios and in specific gynecological contexts, but results are not consistent enough to establish a reliable effect, and NIH ODS does not maintain a fact sheet on this ingredient. Most robust data comes from laboratory and animal studies, which do not reliably predict human outcomes at supplement doses.

Where we looked

There was no paper to cite here, so this is the search instead — run it yourself and see what we saw.

• PubMed: 8 records · searched August 2026"Indole-3-Carbinol"[Title/Abstract] AND ("dietary supplements"[MeSH] OR supplementation[Title/Abstract] OR supplement[Title/Abstract] OR supplements[Title/Abstract] OR "oral administration"[Title/Abstract]) AND (randomized controlled trial[pt] OR clinical trial[pt] OR meta-analysis[pt] OR systematic review[pt]) AND humans[MeSH]
• PubMed: 1195 records · searched August 2026"Indole-3-Carbinol"[Title/Abstract]

This says what this database holds under these terms. It is not a finding that no research exists.

Context

Human studies have used a range of doses and durations, often in small, short-term trials focused on biomarkers like the 2-hydroxyestrone to 16-alpha-hydroxyestrone ratio rather than clinical outcomes. Findings have not been consistently replicated, and the compound is unstable, breaking down into other byproducts (including diindolylmethane, DIM) once ingested, which complicates interpreting what is actually being measured in these trials.