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

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

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 I3C (indole-3-carbinol) used for?

I3C (indole-3-carbinol) is a compound from cruciferous vegetables used to support healthy estrogen metabolism and hormonal balance. In the stomach it converts into DIM and other compounds, so the two are closely related.

I3C or DIM, which should I take?

I3C is the precursor that converts to DIM (and other compounds) in the body, but this conversion is variable and produces a mix of substances. Many people prefer DIM for a more consistent, defined active. Both target estrogen metabolism.

How much I3C should I take?

Doses commonly range from about 200 to 400 mg per day; follow product labeling. Take it with food for absorption.

Is I3C safe?

It is generally well tolerated at typical doses. Because it affects hormone metabolism and can interact with medications, those with hormone-sensitive conditions or on prescriptions should check with a doctor. Very high doses are not recommended.

What is Indole-3-Carbinol?

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.

What is Indole-3-Carbinol used for?

Indole-3-Carbinol is researched primarily for Women's Health and Men's Health. trial showed I3C 400 mg/day shifted estrogen metabolism toward favorable 2-hydroxyestrone:16-alpha-hydroxyestrone ratio. Foundational mechanism — same effect as DIM.

What is the recommended dosage of Indole-3-Carbinol?

The clinically studied dose 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 the product label and check with a healthcare provider for personal advice.

Is Indole-3-Carbinol safe, and does it have side effects?

For most healthy adults, Indole-3-Carbinol is well tolerated at studied doses. Reported effects can include: Generally well-tolerated. GI distress (nausea, stomach pain). It may also interact with some medications. Indole-3-Carbinol is not right for everyone, so check with a healthcare provider first if you are pregnant or breastfeeding, have a medical condition, or take prescription medication.

Does Indole-3-Carbinol interact with any medications?

Possible interactions include: Oral contraceptives — induces estrogen metabolism; may reduce contraceptive efficacy; consult; consider backup. Tamoxifen — theoretical interaction; consult oncologist. If you take prescription medication, check with a pharmacist or doctor before using it.

How strong is the scientific evidence for Indole-3-Carbinol?

NutraSmarts rates the evidence for Indole-3-Carbinol as Limited (2 out of 5). It is backed by 2 clinical trials and 2 cited references summarized on this page. A higher rating reflects more, larger, and better-designed human studies.

References(2 citations)

Evidence ratings on NutraSmarts are based on the totality of human clinical research, with emphasis on randomized controlled trials, meta-analyses, and systematic reviews. The references below directly support claims made throughout this page.

  1. Bell MC, Crowley-Nowick P, Bradlow HL, Sepkovic DW, Schmidt-Grimminger D, Howell P, Mayeaux EJ, Tucker A, Turbat-Herrera EA, Mathis JM Placebo-controlled trial of indole-3-carbinol in the treatment of CIN. Gynecologic Oncology. 2000;78(2):123-9. doi: 10.1006/gyno.2000.5847.PubMedUsed to support: Human placebo-controlled RCT of I3C (200-400 mg/day) in women with cervical intraepithelial neoplasia (CIN 2/3); regression of CIN seen in I3C group vs. placebo; primary human evidence for Cervical Dysplasia Adjunct and Estrogen Metabolism Modulation benefits.
  2. Soldatskiĭ IuL, Onufrieva EK, Steklov AM, Gasparian SF, Strygina IuV The results of adjuvant therapy of juvenile recurring respiratory papillomatosis with the use of indole-3-carbinol. Vestnik Otorinolaringologii. 2011;(5):47-50..PubMedUsed to support: Human clinical study of I3C as adjuvant therapy in juvenile recurrent respiratory papillomatosis (HPV-caused); supports the Recurrent Respiratory Papillomatosis (RRP) Adjunct benefit.