Evidence-based·Last reviewed May 30, 2026·How we grade evidence

Indole-3-Carbinol (I3C)

PhytochemicalIndoleBest with a meal

Useful mainly for limited; mainly studied for estrogen metabolism and specific lesions.

Quick decision guide

May help most

limited; mainly studied for estrogen metabolism and specific lesions

Common dosing range

200-400 mg/day with food

When to expect effects

Weeks

Watch out for

avoid high doses long-term; mixed cancer signals in animals

What is it

Indole-3-carbinol (I3C) is a compound produced when cruciferous vegetables (broccoli, cabbage, Brussels sprouts) are chopped, chewed, or otherwise damaged, releasing it from its glucosinolate precursor glucobrassicin. In the stomach, I3C converts to diindolylmethane (DIM) and other compounds.

Is it worth it for you?

Use this as a quick fit check, not a diagnosis.

Worth considering if…

You are exploring estrogen-metabolism support with a clinician

You accept evidence is largely biomarker-based

You stay at or below 200-400 mg/day

Probably skip if…

You want proven cancer prevention

You are pregnant or breastfeeding

You take hormonal contraception, HRT, or drugs cleared by CYP1A2

Evidence at a glance

Goal	Effect	Best fit	Time
estrogen metabolism Limited Evidence	Shifts estrogen metabolite ratio	Adults interested in modulating estrogen metabolite ratios	Weeks
recurrent respiratory papillomatosis Limited Evidence	Possible reduction in papilloma growth in some patients	Patients with recurrent respiratory papillomatosis, under specialist care	Months
cervical dysplasia Mixed Evidence	Inconsistent	Not established as a treatment	Months

estrogen metabolism

Limited Evidence

Effect: Shifts estrogen metabolite ratio
Best fit: Adults interested in modulating estrogen metabolite ratios
Time: Weeks

recurrent respiratory papillomatosis

Limited Evidence

Effect: Possible reduction in papilloma growth in some patients
Best fit: Patients with recurrent respiratory papillomatosis, under specialist care
Time: Months

cervical dysplasia

Mixed Evidence

Effect: Inconsistent
Best fit: Not established as a treatment
Time: Months

Evidence for 3 uses

AI-assisted evidence assessment — talk to your doctor before relying on any single supplement.

estrogen metabolism

Biomarker support

Limited Evidence

I3C converts in stomach acid mainly to diindolylmethane, which promotes 2-hydroxylation of estradiol, raising 2-hydroxyestrone and lowering 16-alpha-hydroxyestrone. This is a measured shift in estrogen metabolite ratios, a biomarker change that has not been shown to translate into symptom relief or disease prevention.

Effect size

Shifts estrogen metabolite ratio

Time to effect

Weeks

Best fit

Adults interested in modulating estrogen metabolite ratios

Bottom line: I3C shifts estrogen metabolite ratios, but this biomarker change has no proven clinical benefit.

SourceMcAlindon et al., 2001 — PubMed

recurrent respiratory papillomatosis

Disease adjunct

Limited Evidence

Small studies suggest I3C may slow papilloma regrowth in a subset of patients with recurrent respiratory papillomatosis, possibly via effects on estrogen metabolism and the aryl hydrocarbon receptor. Evidence is from small, uncontrolled or preliminary trials.

Effect size

Possible reduction in papilloma growth in some patients

Time to effect

Months

Best fit

Patients with recurrent respiratory papillomatosis, under specialist care

Bottom line: May help a subset of recurrent respiratory papillomatosis patients, on preliminary evidence.

SourceRosen et al., 2004 — PubMed Rosen et al., 1998 — PubMed

cervical dysplasia

Disease adjunct

Mixed Evidence

A few small trials examined I3C for cervical intraepithelial neoplasia with inconsistent results, and it is not a substitute for standard surveillance or treatment. Animal studies show both protective and tumor-promoting effects depending on context, which cautions against high-dose long-term use.

Effect size

Inconsistent

Time to effect

Months

Best fit

Not established as a treatment

Less likely

People relying on it instead of standard gynecologic management

Bottom line: Evidence for cervical dysplasia is inconsistent; not a substitute for standard care.

Evidence is mixed

Small trials conflict, and animal data show both protective and tumor-promoting effects.

SourceBell et al., 2000 — PubMed· conflicting Auborn et al., 2006 — PubMed· conflicting

SourceBell et al., 2000 — PubMed Auborn et al., 2006 — PubMed

How it works

I3C is unstable in stomach acid and rapidly converts to a mixture of acid-condensation products, with diindolylmethane (DIM) being the most abundant. The biological effects attributed to I3C are largely mediated by DIM and related condensation products. These compounds modulate estrogen metabolism by promoting hydroxylation at the C-2 position of the estradiol molecule, producing 2-hydroxyestrone (considered a less hormonally active metabolite) and reducing the formation of 16-alpha-hydroxyestrone. This shift is the primary mechanism proposed for I3C's effects on hormone-related conditions. Research suggests I3C and its metabolites also activate the aryl hydrocarbon receptor (AhR), influencing phase I and phase II detoxification enzymes. Preclinical evidence shows effects on cell cycle, apoptosis, and inflammation. Higher doses of I3C have shown both beneficial and adverse effects in animal models, with some studies suggesting tumor-promoting effects in certain contexts, raising caution about high-dose long-term use.

How to take it

1. Typical dose

200-400 mg/day

2. Timing

Once or twice daily

3. With food

With a meal containing some fat for absorption

4. How long to try

Weeks to evaluate hormonal effects; avoid high-dose long-term use

What to track

GI tolerance and headache

Any rash, dizziness, or tremor

Hormonal symptoms with clinician oversight

2 commercial forms

Compare the main delivery options and what they’re best suited for.

I3C capsules

Common form. Stability and conversion are unpredictable, leading many practitioners to prefer DIM instead.

I3C is unstable in stomach acid; absorption involves conversion to multiple products.

I3C combined with DIM

Marketed as providing comprehensive estrogen metabolism support.

Provides both precursor and primary metabolite.

Safety

Know the common side effects, key cautions, and who should avoid it.

Common side effects

NauseaGI upsetHeadache

Serious risks

High doses may cause transient rash, dizziness, or tremor
Mixed protective and tumor-promoting effects in animal models

Who should avoid it

Pregnant or breastfeeding people
People with hormone-sensitive cancers without oncologist input

Pregnancy & breastfeeding

Avoid in pregnancy and breastfeeding due to hormonal effects and insufficient safety data.

Interactions

CYP1A2 substrates (caffeine, theophylline, some antidepressants, beta-blockers)Moderate

I3C induces CYP1A1/1A2, altering their metabolism

Hormonal contraceptives and HRTModerate

May affect metabolism of hormonal medications

TamoxifenModerate

May affect tamoxifen metabolism

Food sources

Food	Amount	%DV
Broccoli (1 cup cooked)	approx 100 mg I3C equivalent	—
Brussels sprouts (1 cup)	Higher I3C content among crucifers	—
Cabbage, raw (1 cup)	approx 75 mg I3C equivalent	—
Kale (1 cup cooked)	Significant I3C content	—
Cauliflower (1 cup)	Moderate I3C content	—

Broccoli (1 cup cooked)

Amount: approx 100 mg I3C equivalent
%DV: —

Brussels sprouts (1 cup)

Amount: Higher I3C content among crucifers
%DV: —

Cabbage, raw (1 cup)

Amount: approx 75 mg I3C equivalent
%DV: —

Kale (1 cup cooked)

Amount: Significant I3C content
%DV: —

Cauliflower (1 cup)

Amount: Moderate I3C content
%DV: —

Choosing a product

What to look for on the label — and what to be skeptical of.

Look for…

Stated I3C dose within 200-400 mg range

Reputable manufacturer

Note that DIM is an alternative with more predictable conversion

Be skeptical of…

Prevents breast or cervical cancer

Detoxifies hormones

Frequently asked questions

Should I take I3C or DIM?⌄

DIM is the more stable downstream product and is often preferred for predictable effects. I3C converts to DIM and other compounds in the stomach, with results that can vary. Many practitioners recommend DIM instead.

How much I3C is in cruciferous vegetables?⌄

A cup of cooked broccoli or Brussels sprouts provides roughly 50-100 mg I3C equivalent. Supplements typically deliver several times this amount.

Is I3C safe for long-term use?⌄

Long-term safety data are limited, and animal studies have raised concerns about high-dose use. Short-term use at typical doses is generally well tolerated.

Can I3C affect my birth control?⌄

I3C induces enzymes that metabolize hormonal contraceptives and may reduce their effectiveness. Consult your clinician about potential interactions.

Why does I3C cause some people to feel different effects each time?⌄

I3C is unstable in stomach acid and converts to a variable mixture of products depending on individual stomach conditions, leading to inconsistent effects. DIM provides more predictable activity.

References by claim

estrogen metabolism

McAlindon et al., 2001 — PubMed (2001) link

recurrent respiratory papillomatosis

Rosen et al., 2004 — PubMed (2004) link

Rosen et al., 1998 — PubMed (1998) link

cervical dysplasia

Bell et al., 2000 — PubMed (2000) link

Auborn et al., 2006 — PubMed (2006) link

Track Indole-3-Carbinol (I3C) with Pilora

Set up dose reminders, check interactions, and join the community in the Pilora iPhone app.

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Evidence-based·Last reviewed May 30, 2026·Evidence current as of May 30, 2026·How we grade evidence

Disclaimer: These statements have not been evaluated by the FDA. This page is educational, not a substitute for personalized medical advice. Evidence grades are AI-assisted assessments — talk to your doctor before starting any new supplement, especially if you’re pregnant, breastfeeding, on medications, or managing a chronic condition.