Indole-3-Carbinol

I3C

Snapshot

Indications	Contraindications
Estrogen metabolism support^1–3 Cervical dysplasia⁴ Vulvar intraepithelial neoplasia⁴ Recurrent respiratory papillomatosis⁵ Benign prostatic hyperplasia⁶	Pregnancy or nursing⁷ Under age 18⁷

Indole-3-carbinol (I3C) is the breakdown product of glucosinolates in cruciferous vegetables such as broccoli, cabbage, and Brussels sprouts⁴. It shifts estrogen metabolism toward the 2-hydroxylated pathway^{1, 3}. Supplementation is used for breast cancer risk reduction in women at increased risk, and for precancerous cervical and vulvar lesions⁴. It is also used in recurrent respiratory papillomatosis and for prostate health.

Human data rest largely on biomarker endpoints.^{2, 3} Urinary estrogen metabolite ratios rose with indole-3-carbinol in women at increased breast cancer risk in two small trials lasting four to eight weeks; neither tested whether the rise was sustained longer^{2, 3}. Memorial Sloan Kettering states that I3C has cancer-preventive effects but has not been shown to treat cancer in humans, and some animal studies suggest tumor promotion⁴. An uncontrolled phase I trial in recurrent respiratory papillomatosis found papilloma growth stopped in some patients⁵. A 2026 systematic review of a combined I3C and epigallocatechin-3-gallate supplement in men reported lower benign prostatic hyperplasia symptom severity⁶. There are 332 products listing I3C, sampled as capsules; see Form comparison.

The main interaction concern is enzyme induction: I3C raised cytochrome P450 1A2 (CYP1A2) activity in nearly all women in a phase I trial³. Memorial Sloan Kettering's patient page lists use with CYP1A2 substrate medications under "Do Not Take if", while noting clinical relevance has yet to be determined⁴.

Last updated October 17, 2026. Read how we make monographs.

In the full monograph

27 sources, 15 studies

When to useThe situations practitioners use it for, each with the reason and the study behind it.
SafetyWho should avoid it, who needs extra care, and the side effects reported in studies.
InteractionsThe medicines and supplements it interacts with, the effect of each, and what labeling says to watch.
Protocol notesThe doses used in studies, how and when they were taken, and how the forms on the market compare.
How it worksWhat it is and how it works in the body, in plain terms.
Published studiesThe studies behind each use, popular claims checked against them, and trials still under way.
Word of mouthWhat patients and practitioners report online, kept separate from the clinical evidence.
Clinical perspectiveA closing read of where the evidence is solid, where it is thin, and what has not been studied.

Snapshot

In the full monograph

Sources