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📰Read the full Indole-3-Carbinol evidence review on GMJ News →Complete clinical article, references and updates on news.gmj.ge. This page is the structured safety summary.⚠ Patient on theophylline/clozapine adding I3C — potent CYP1A2 inducer; drug levels may drop [1]
⚠ Patient on PPIs taking I3C — reduced acid-dependent conversion; switch to DIM [1]
⚠ Patient taking I3C for 'cancer prevention' — no phase III data; eat cruciferous vegetables instead [1]
⚠ Patient on tamoxifen using I3C — discuss with oncologist; interaction complex [1]
🥗 Food first — build your daily Typical 200–400 mg
Check the foods you regularly eat — the bar fills toward your daily target.
Broccoli (100 g, raw)50 mg I3C precursor (glucobrassicin) per 100 g
Brussels sprouts (100 g)60 mg I3C precursor (glucobrassicin) per 100 g
Cabbage (100 g)40 mg I3C precursor (glucobrassicin) per 100 g
Cauliflower (100 g)30 mg I3C precursor (glucobrassicin) per 100 g
Check your regular foods above
🔬 Lab interpreter
Recommended test
Drug levels if on CYP1A2 medications
Drug levels if on CYP1A2 medications
Reference range / target
Therapeutic ranges
Therapeutic ranges
Potent CYP1A2 induction [1].
Full lab monitoring ↓⚕ For professionals — confirm ranges against your local laboratory.
Clinical verdict
I3C/DIM modulates estrogen metabolism (2/16 OHE1 ratio shift) — a pharmacologically validated mechanism. The only clinical niche with repeated evidence is recurrent respiratory papillomatosis (RRP). For cancer prevention, the mechanism is promising but no phase III trial exists. DIM preferred over I3C for bioavailability. CYP1A2 induction is a clinically significant drug interaction [1] [2].
1 How much do I need?
👤 Adults: Specific dosage data under clinical review
👴 Elderly: Specific dosage data under clinical review
🤰 Pregnancy: See guidance
Avoid. Estrogen metabolism modulation effects on fetal development unknown [1].
👦 Pediatric: See guidance
Not studied in children. Avoid concentrated supplements [1].
🏃 Athletes: Standard dose
⚖️ Obesity: Standard dose
Fat-soluble compounds may require dose adjustment in obesity.
🩺 Renal: Consult specialist
Dose adjustment may be needed in renal impairment.
🌱 Vegan: Standard dose
How to take
🍽 Timing: With food (acid aids I3C conversion; fat aids DIM absorption) [1].
💊 With food: With a meal [1].
🚫 Avoid: I3C with PPIs (reduced conversion). During pregnancy. With CYP1A2 drugs without monitoring [1].
2 Which form?
| Form | Bioavailability | Vegan | Cost |
|---|---|---|---|
| ['I3C capsules (200–400 mg)', 'traditional', 'Requires stomach acid for conversion to DIM. Variable conversion efficiency [1].'] | Standard | Check label | |
| ['DIM capsules (100–200 mg)', 'preferred', 'Bypasses acid-dependent conversion step. More predictable bioavailability [1].'] | Standard | Check label | |
| ['BioResponse DIM® (enhanced absorption)', 'clinical', 'Microencapsulated DIM with improved absorption. Used in clinical studies [1].'] | Standard | Check label |
3 Common questions
I3C or DIM — which should I take? ▼
DIM is generally preferred because: (1) it's the actual active metabolite; (2) its formation from I3C depends on stomach acid (PPIs may reduce conversion); (3) DIM has more predictable bioavailability. I3C at high doses also forms undesirable condensation products in the stomach. DIM 100–200 mg/day is equivalent to I3C 300–400 mg/day [1].
Can I3C/DIM prevent breast cancer? ▼
The mechanism is promising (favorable estrogen metabolism shift), and epidemiological data on cruciferous vegetable intake are supportive, but NO phase III cancer prevention trial has been completed. It is premature to recommend I3C/DIM for cancer prevention. Eating cruciferous vegetables (which provide I3C among many other compounds) is recommended [1].
Does I3C interact with PPIs? ▼
Potentially. I3C requires stomach acid for conversion to DIM and other active metabolites. Proton pump inhibitors raise gastric pH, which could reduce I3C conversion. This is another reason to prefer DIM supplements — they bypass this step [1].
What is the 2/16 estrogen ratio? ▼
Estrogens are metabolized to either 2-hydroxyestrone (2-OHE1, considered protective) or 16α-hydroxyestrone (16α-OHE1, considered proliferative). A higher 2/16 ratio is associated with lower breast cancer risk in epidemiological studies. I3C/DIM shifts this ratio toward the favorable 2-hydroxylation pathway [1].
4 Clinical evidence
Strong
No Cochrane review. Estrogen metabolite ratio modulation is well-documented biochemically [1]. HIGH
Moderate
Recurrent respiratory papillomatosis: I3C 200 mg BID halted or reversed papilloma growth in ~33% of patients in clinical studies (the only condition with repeated clinical documentation) [2]. Estrogen metabolism: multiple studies confirm I3C/DIM shifts urinary 2-OHE1/16α-OHE1 ratio favorably at 300–400 mg/day I3C or 100–200 mg/day DIM [1]. Cervical dysplasia (CIN): 1 pilot study showed regression of CIN II/III in some patients; needs larger RCTs [1]. MODERATE
Insufficient
Breast cancer prevention: estrogen metabolism shift is promising but no completed phase III prevention trial. Epidemiological data on cruciferous vegetable intake and breast cancer are supportive but not supplement-specific [1]. Prostate cancer: preclinical anti-androgen activity; no clinical trials [1]. Weight management: preliminary data on adipose estrogen modulation; insufficient [1]. LOW
5 Safety, toxicity & adverse events
Relative
⚠ Hormone-sensitive conditions — alters estrogen metabolism
⚠ Induces CYP1A2/CYP3A4 — can change drug levels
⚠ Pregnancy and lactation — avoid supplemental doses
🚩 Red flags
● Patient on narrow-index CYP1A2 drug adding I3C — drug level reduction [1]
● Patient using I3C as cancer treatment — it is not a proven cancer therapy [1]
6 Interactions
Drug interactions
Theophylline / Clozapine (CYP1A2 substrates) Major
Mechanism: I3C potently induces CYP1A2 [1].
Effect: Reduced drug levels; potential loss of efficacy [1].
Action: Monitor drug levels. Consider dose adjustment [1].
Supplement synergies
Sulforaphane · 100 mg DIM + 30 mg sulforaphane
Complementary cruciferous pathways: I3C/DIM (estrogen metabolism) + sulforaphane (Nrf2/detoxification) [1].
Complementary cruciferous pathways: I3C/DIM (estrogen metabolism) + sulforaphane (Nrf2/detoxification) [1].
Calcium D-Glucarate · 200 mg DIM + 500 mg calcium D-glucarate
Supports glucuronidation — the phase II pathway for estrogen conjugation [1].
Supports glucuronidation — the phase II pathway for estrogen conjugation [1].
7 Regulatory
United States (FDA): Available as dietary supplement. Not FDA-approved for cancer prevention [1].
NCI: National Cancer Institute has funded I3C/DIM research but no approved cancer indication [1].
8 US supplement products
1
on-market products containing Indole-3-Carbinol (NIH DSLD)
Brands carrying Indole-3-Carbinol (1)
Click a brand to see its Indole-3-Carbinol products.
9 References (4)
[1]Aggarwal BB, Ichikawa H. Molecular targets and anticancer potential of indole-3-carbinol and its derivatives. Cell Cycle. 2005;4(9):1201-1215. doi:10.4161/cc.4.9.1993 REVIEW Accessed: 2026-05-29
[2]Rosen CA, et al. Preliminary results of the use of indole-3-carbinol for recurrent respiratory papillomatosis. Otolaryngol Head Neck Surg. 1998;118(6):810-815. doi:10.1016/S0194-5998(98)70274-8 REVIEW Accessed: 2026-05-29
[3]Thomson CA, et al. Chemopreventive properties of 3,3'-diindolylmethane in breast cancer: evidence from experimental and human studies. Nutr Rev. 2016;74(7):432-443. doi:10.1093/nutrit/nuw010 REVIEW Accessed: 2026-05-29
[4]Dalessandri KM, et al. Pilot study: effect of 3,3'-diindolylmethane supplements on urinary hormone metabolites in postmenopausal women with a history of early-stage breast cancer. Nutr Cancer. 2004;50(2):161-167. doi:10.1207/s15327914nc5002_5 REVIEW Accessed: 2026-05-29
10 Cite this page
Vancouver: Pkhakadze G. Indole-3-Carbinol — safety profile [Internet]. Tbilisi: PHIG; 2026 [cited 2026 Jun 15]. Available from: https://supplement.ge/ingredients/i3c/
APA 7th: Pkhakadze, G. (2026). Indole-3-Carbinol — Safety profile. Public Health Institute of Georgia. https://supplement.ge/ingredients/i3c/
📋 Editorial information
Author: Prof. G. Pkhakadze, MD, MPH, PhD
Institution: Public Health Institute of Georgia (PHIG)
Affiliation: David Tvildiani Medical University (DTMU)
First published: January 2026
Last reviewed: 2026-05-29
Next review: December 2026
References: 4 cited sources
COI: SupplementIndex receives no funding from supplement manufacturers. All content independently authored by PHIG.
Process: Systematic literature review
📄 License & reuse
Published under Creative Commons Attribution 4.0 International (CC BY 4.0). You may share and adapt for any purpose with attribution.
Pkhakadze G. "Indole-3-Carbinol — Safety Profile." SupplementIndex, PHIG, 2026. https://supplement.ge/ingredients/i3c/ CC BY 4.0.
GP
Prof. G. Pkhakadze, MD, MPH, PhD
Professor of Public Health · Head of Department, DTMU
Editor-in-Chief, Georgian Medical Journal (ISSN 3088-4322)
Chair, Public Health Institute of Georgia · UEMS Public Health Section
Educational and public health purposes. CC BY 4.0. Consult your healthcare provider before starting any supplement. Corrections: info@accreditation.ge. Publisher: PHIG