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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.

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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.

How to take it

TimingTiming does not matter.
With food?With food, which reduces the nausea I3C commonly causes.
Worth knowingI3C only becomes DIM in stomach acid, so if you take a proton-pump inhibitor a DIM product skips a step that may not be happening for you.

Interactions

With medications

  • combined oral contraceptives

    I3C induces cytochrome P450 enzymes and may lower hormone levels enough to reduce reliability. use additional contraception and talk to your doctor

  • drugs metabolised by CYP1A2 and CYP3A4 (including theophylline, clozapine and many others)

    Enzyme induction can lower blood levels and reduce their effect. check your prescriptions with a pharmacist before starting

Well-established interactions only — this is not a complete list. Always tell your doctor and pharmacist what you take.

Frequently asked questions

What does indole-3-carbinol do for estrogen?

Indole-3-carbinol measurably shifts the ratio of estrogen metabolites (2-hydroxyestrone to 16α-hydroxyestrone) in a placebo-controlled trial. That is a biomarker change, and whether it produces any clinical benefit is unresolved, so the evidence is limited.

Does indole-3-carbinol help cervical dysplasia?

The evidence is limited and inconsistent: a small trial in cervical intraepithelial neoplasia reported regression in about half of women taking I3C, but a later trial in vulvar lesions found no advantage over placebo. Both enrolled only a few dozen people.

Does indole-3-carbinol interact with birth control?

Yes: I3C induces cytochrome P450 enzymes and may lower hormone levels enough to make combined oral contraceptives less reliable, so use additional contraception and talk to your doctor. It can also lower levels of drugs such as theophylline and clozapine.

How much indole-3-carbinol should I take?

Trials in precancerous lesions used 200-400 mg of indole-3-carbinol daily, and retail capsules typically supply 200 mg. Take it with food to reduce nausea; higher doses have been linked to balance and tremor problems.

Scientific references

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