What is it?
What Indole-3-carbinol is
2Indole-3-carbinol, or I3C, forms when glucobrassicin from cruciferous vegetables breaks down. A capsule of isolated I3C is not the same exposure as eating broccoli, cabbage, kale, or Brussels sprouts.
Names, aliases and forms
Mechanisms of action
Estrogen-metabolism shift
3Human studies report shifts in estrogen-metabolite ratios after I3C. That is why I3C is marketed for hormone support, but the marker shift is not the same as a proven disease-prevention, fertility, testosterone, or mood effect.
I3C versus DIM
2I3C can form acid-condensation products such as DIM in the stomach, but I3C, DIM, cruciferous vegetables, and blended hormone-support formulas are distinct exposures and products.
Potential effects and evidence map
Reviewed I3C evidence includes a small human estrogen-metabolism study, small gynecologic research studies, and a phase I study in high-risk women. These findings are population- and context-specific, not cognitive outcomes or a consumer-use framework. Animal toxicology does not establish the safety of concentrated, long-term self-use.
Typical dosages and timing
Separate small studies included 200 mg and 400 mg daily arms. A phase I study in high-risk women used 400 mg daily before 800 mg daily. These research protocols do not establish a consumer amount, route, timing, or repeat-use plan.
Timing & effect horizon
Reliable onset, duration, half life, tolerance, and cycling data for cognitive or mood use were not found. Estrogen-metabolite studies measured changes over weeks to months.
Safety, side effects and risk profile
I3C changes estrogen-metabolism markers, so caution is appropriate with hormone-sensitive conditions or hormone therapy.
I3C can induce CYP1A2 in human studies and MSKCC warns that CYP1A2 substrate drug effectiveness may be reduced.
Avoid concentrated I3C during pregnancy or lactation unless a clinician specifically directs use.
GI effects and rash are plausible; NTP and animal work point to intestine as a toxicity target in some models.
MSKCC notes rare small ALT increases, and I3C strongly affects xenobiotic-metabolism pathways.
NTP rodent findings and mixed preclinical cancer models make high-dose, long-term self-use a poor extrapolation from vegetable intake.
In the phase I study, CYP1A2 activity rose after I3C. MSKCC warns that lab and human evidence suggest I3C may affect CYP1A2 substrate drugs, with clinical relevance still uncertain.
Because I3C changes estrogen-metabolism markers, people with hormone-sensitive cancers, endometriosis, fibroids, fertility care, hormone therapy, oral contraceptives, or anti-estrogen drugs should seek individual clinical guidance rather than self-experimenting.
NTP rodent gavage studies found different carcinogenicity conclusions by species and sex, including clear evidence in male mice for liver neoplasms and some evidence in female rats for uterine neoplasms. This argues against assuming high-dose long-term supplement use is benign.
Interactions and cautions
Review I3C with CYP1A2 substrate drugs, hormone therapy, oral contraceptives, anti-estrogen drugs, chemotherapy or cancer-care plans, immunosuppressive conditions, caffeine sensitivity, smoking changes, and liver-risk medication combinations.
Legal and regulatory status
United States, as of 2026: this evidence page does not determine whether a specific I3C product or its claims comply with law. Product and claim requirements can differ in other jurisdictions.
Practical buying and quality notes
- The only indexed product row is I3C Indole-3-Carbinol 200 mg capsules, but it is marked unavailable in current variant data. Use it as historical listing context only.8
- For I3C products, compare whether the product is I3C or DIM, the mg per capsule, serving count, lot testing, excipients, storage, expiry, and whether it is a single-ingredient product or a hormone-support blend.8
- Cruciferous vegetables provide glucosinolate precursors in a food matrix. A 200 mg isolated I3C capsule is a concentrated and chemically different exposure from normal dietary servings.2
FAQ
What is Indole-3-carbinol?
1Indole-3-carbinol is a plant indole formed from glucobrassicin in cruciferous vegetables. It is commonly abbreviated I3C.
What amounts appeared in I3C studies?
5The cited small trials and phase I study used differing protocol amounts. They do not establish a consumer amount, route, timing, or long-term self-use plan.
Does I3C help focus or memory?
3No reliable human focus, memory, mood, or productivity evidence was found. The better-supported human context is estrogen-metabolism markers and small gynecologic dysplasia studies.
Is I3C the same as DIM?
2No. DIM can form from I3C under acidic conditions, and both appear in related supplement markets, but they are distinct compounds with different product labels and evidence boundaries.
Who should avoid I3C?
2Seek individual clinical guidance with pregnancy, lactation, hormone-sensitive conditions, cancer-care plans, hormone therapy, anti-estrogen drugs, oral contraceptives, liver disease, abnormal liver enzymes, CYP1A2 substrate drugs, or complex medication plans.
References
- PubChem. Indole-3-carbinol (CID 3712). Accessed 2026-07-01.
- Memorial Sloan Kettering Cancer Center. Indole-3-Carbinol. Accessed 2026-07-01.
- Michnovicz JJ, et al. Changes in levels of urinary estrogen metabolites after oral indole-3-carbinol treatment in humans. J Natl Cancer Inst. 1997;89(10):718-723.
- Bell MC, et al. Placebo-controlled trial of indole-3-carbinol in the treatment of CIN. Gynecol Oncol. 2000;78(2):123-129.
- Reed GA, et al. A phase I study of indole-3-carbinol in women: tolerability and effects. Cancer Epidemiol Biomarkers Prev. 2005;14(8):1953-1960.
- Naik R, et al. A randomized phase II trial of indole-3-carbinol in the treatment of vulvar intraepithelial neoplasia. Int J Gynecol Cancer. 2006;16(2):786-790.
- National Toxicology Program. Toxicology and carcinogenesis studies of indole-3-carbinol. Technical Report 584. July 2017.
- NootropicsIndex indexed listing. I3C Indole-3-Carbinol 200 mg capsules. Accessed 2026-07-01.