Limited evidenceWomen's health

Indole-3-Carbinol (I3C)

A compound from cruciferous vegetables that measurably shifts estrogen metabolite ratios. Whether that shift produces any clinical benefit is still unresolved, and the trials in precancerous lesions are small and inconsistent.

Evidence last reviewed: August 2026

What the science says

Estrogen metabolite ratio Limited evidence
A randomized, double-blind, placebo-controlled crossover trial of an I3C-containing formula in premenopausal women reported a change in the 2-hydroxyestrone to 16α-hydroxyestrone ratio. This is a biomarker, and its link to disease outcomes has not been established.
Cervical and vulvar precancerous lesions Limited evidence
A small placebo-controlled trial in cervical intraepithelial neoplasia reported regression with I3C in about half of treated women, but a later randomized phase II trial in vulvar intraepithelial neoplasia found no significant advantage over placebo. Both trials enrolled a few dozen participants.

Dosage & safety

Studied doseTrials in precancerous lesions used 200-400 mg of I3C daily. Retail capsules typically supply 200 mg; many products use DIM, the stomach-acid condensation product of I3C, instead.

SafetyCan cause nausea and, at higher doses, balance and tremor problems have been reported. I3C induces cytochrome P450 enzymes and may reduce blood levels of a range of drugs, including some oral contraceptives. Avoid in pregnancy and breastfeeding.

Scientific references

Placebo-controlled trial of indole-3-carbinol in the treatment of CIN
Bell MC, Crowley-Nowick P, Bradlow HL, Sepkovic DW, Schmidt-Grimminger D, Howell P — Gynecol Oncol, 2000
A randomized phase II trial of indole-3-carbinol in the treatment of vulvar intraepithelial neoplasia
Naik R, Nixon S, Lopes A, Godfrey K, Hatem MH, Monaghan JM — Int J Gynecol Cancer, 2006
A randomized, double-blind, placebo-controlled, cross-over trial to evaluate the effect of EstroSense(®) on 2-hydroxyestrone:16α-hydroxyestrone ratio in premenopausal women
Green T, See J, Schauch M, Reil J, Glover M, Brix J — J Complement Integr Med, 2023

Where to buy

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