Home Ingredients Indole-3-Carbinol (I3C)
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Indole-3-Carbinol (I3C)

Evidence Level
Limited
2 Clinical Trials
5 Documented Benefits
2/5 Evidence Score

I3C is a glucosinolate-derived compound found in cruciferous vegetables — formed when raw vegetables are chewed/cut, releasing the enzyme myrosinase that converts glucobrassicin to I3C. In the stomach, I3C converts to DIM and other condensation products. Used for similar applications as DIM (estrogen metabolism, recurrent respiratory papillomatosis, detoxification) but with more variable conversion to active forms. Older clinical evidence base than DIM in some indications.

Studied Dose 200-400 mg/day for general use; 200 mg twice daily used in some trials; recurrent respiratory papillomatosis trials used 400 mg/day
Active Compound Indole-3-carbinol (I3C); active metabolites include DIM, ascorbigen, indolocarbazole

Benefits

Estrogen Metabolism Modulation

trial showed I3C 400 mg/day shifted estrogen metabolism toward favorable 2-hydroxyestrone:16-alpha-hydroxyestrone ratio. Foundational mechanism — same effect as DIM.

Supported by Trial 1

Recurrent Respiratory Papillomatosis (RRP) Adjunct

trial showed I3C reduced papilloma recurrence in patients with juvenile/adult RRP. Mechanism: anti-HPV effects, immune modulation. Modest clinical evidence; adjunct only.

Supported by Trial 2

Cervical Dysplasia Adjunct

trial showed I3C reduced CIN 2/3 progression vs placebo. Similar mechanism to DIM. Adjunct only — standard screening/treatment foundational.

Supported by Trial 2

Phase I & II Detoxification Support

Induces both Phase I (CYP enzymes) and Phase II (sulfation, glucuronidation, glutathione conjugation) detoxification — supports clearance of estrogens, environmental toxins, drugs.

Antioxidant / Anti-Inflammatory

Modest direct antioxidant activity plus support of endogenous antioxidant systems. Anti-inflammatory effects via NF-κB modulation.

Mechanism of action

1

Conversion to DIM and Other Active Metabolites

I3C itself is largely converted in the acidic stomach environment to DIM (3,3'-diindolylmethane), ascorbigen, and indolo[3,2-b]carbazole (ICZ). I3C is essentially a 'pro-drug' for these active metabolites — DIM is the most studied.

2

CYP1A1/CYP1A2 Induction (Same as DIM)

Promotes estrogen 2-hydroxylation pathway. Same fundamental mechanism as DIM since I3C converts to DIM.

3

Aryl Hydrocarbon Receptor (AhR) Activation

ICZ (indolocarbazole) — an I3C metabolite — is one of the most potent natural AhR ligands. Activates extensive xenobiotic metabolism gene expression.

4

Anti-HPV Effects

Antiviral activity against HPV in cell culture. Mechanism for cervical dysplasia and RRP applications.

Clinical trials

1
I3C for Estrogen Metabolism — Bradlow 1999
PubMed

Trial of I3C (400 mg/day) in healthy women for 2 months measuring urinary estrogen metabolites.

Healthy women.

Significantly increased 2-OH:16-alpha-OH estrogen metabolite ratio. Established I3C effects on estrogen metabolism.

2
I3C for Recurrent Respiratory Papillomatosis — Rosen 1998
PubMed

Trial of I3C (400 mg/day) in patients with recurrent respiratory papillomatosis.

RRP patients.

Reduced recurrence rate in some patients. Generated interest in I3C as RRP adjunct. Limited subsequent confirmatory research.

Side effects and drug interactions

Common Potential side effects

Generally well-tolerated.
GI distress (nausea, stomach pain).
Skin rash (rare).
Headache.
Tremor / unsteadiness at higher doses (rare).
Liver enzyme elevations rare.
Hormonal symptoms in sensitive individuals (mood changes, menstrual irregularities).

Important Drug interactions

ORAL CONTRACEPTIVES — induces estrogen metabolism; may reduce contraceptive efficacy; consult; consider backup.
TAMOXIFEN — theoretical interaction; consult oncologist.
CYP1A2 substrates (caffeine, tizanidine, theophylline) — induces CYP1A2; reduces drug levels.
CYP3A4 substrates — modest induction; theoretical interactions.
Warfarin — case reports of increased INR with I3C; monitor.
Hormone-sensitive cancers — consult oncologist.
Pregnancy/lactation — limited safety data; AVOID.

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Frequently asked questions about Indole-3-Carbinol (I3C)

What is Indole-3-Carbinol (I3C)?

I3C is a glucosinolate-derived compound found in cruciferous vegetables — formed when raw vegetables are chewed/cut, releasing the enzyme myrosinase that converts glucobrassicin to I3C.

What does Indole-3-Carbinol (I3C) do?

I3C itself is largely converted in the acidic stomach environment to DIM (3,3'-diindolylmethane), ascorbigen, and indolo[3,2-b]carbazole (ICZ). I3C is essentially a 'pro-drug' for these active metabolites — DIM is the most studied. In clinical research, Indole-3-Carbinol (I3C) has been studied for estrogen metabolism modulation, recurrent respiratory papillomatosis (rrp) adjunct, cervical dysplasia adjunct.

Who should take Indole-3-Carbinol (I3C)?

Indole-3-Carbinol (I3C) may be most relevant for people interested in women's health, men's health. It has been clinically studied for estrogen metabolism modulation, recurrent respiratory papillomatosis (rrp) adjunct, cervical dysplasia adjunct. As with any supplement, consult your healthcare provider before starting, especially if you have medical conditions or take prescription medications.

How long does Indole-3-Carbinol (I3C) take to work?

Most clinical trial effects appear over weeks of consistent use; individual response varies. Acute or same-day effects (where applicable) typically appear within hours, but most cumulative benefits — particularly those affecting biomarkers, mood, sleep quality, or chronic symptoms — require 4-12 weeks of regular use to fully assess. If you don't notice benefit after 12 weeks at the appropriate dose, it may not be your responder.

When is the best time to take Indole-3-Carbinol (I3C)?

Indole-3-Carbinol (I3C) can typically be taken with breakfast or dinner — taking with food reduces GI sensitivity for most supplements. Specific timing matters less than daily consistency for cumulative effects. Always check product labeling and follow personalized guidance from your healthcare provider.

Is Indole-3-Carbinol (I3C) worth taking?

Indole-3-Carbinol (I3C) has limited clinical evidence (Evidence Level 2/5 on NutraSmarts) — preliminary research suggests potential benefit, but more rigorous trials are needed. Whether it's worth taking depends on your specific goals, what you've already tried, your budget, and your overall supplement strategy. The honest framing: no supplement is essential for most people, and lifestyle factors (sleep, exercise, diet, stress management) typically produce larger effects than any single supplement. Indole-3-Carbinol (I3C) is most worth trying if its evidence-supported uses align with your specific goals.

What is the recommended dosage of Indole-3-Carbinol (I3C)?

The clinically studied dose for Indole-3-Carbinol (I3C) is 200-400 mg/day for general use; 200 mg twice daily used in some trials; recurrent respiratory papillomatosis trials used 400 mg/day. Always follow product labeling and consult a healthcare provider for personalized dosing recommendations.

What is Indole-3-Carbinol (I3C) used for?

Indole-3-Carbinol (I3C) is studied for estrogen metabolism modulation, recurrent respiratory papillomatosis (rrp) adjunct, cervical dysplasia adjunct. trial showed I3C 400 mg/day shifted estrogen metabolism toward favorable 2-hydroxyestrone:16-alpha-hydroxyestrone ratio. Foundational mechanism — same effect as DIM.