Supplement Forms/Alternate Names :

  • I3C


Principal Proposed Uses

Other Proposed Uses

Indole-3-carbinol (I3C), a chemical found in vegetables of the broccoli family, is thought to possess cancer preventive properties.

Indole-3-carbinol appears to work in several ways:

  • Facilitating the conversion of estrogen to a less cancer-promoting form 1-3,6
  • Partially blocking the effects of estrogen on cells 4,6,30
  • Directly killing or inhibiting cancer cells 6
  • Reducing levels of free radicals, which can promote cancer by damaging DNA 5


I3C is found in cruciferous vegetables ( Brassica plants), such as cabbage, broccoli, brussels sprouts, cauliflower, kale, kohlrabi, and turnips. A typical Japanese diet provides the equivalent of about 112 mg of I3C daily; intake in Western diets is lower. 7,8

Therapeutic Dosages

A 4-week, double-blind, placebo-controlled trial of 57 women found that a minimum dose of 300 mg of I3C daily may be necessary to reduce risk of estrogen-promoted cancers. 9 Another study found benefits with 400 mg of I3C per day. 10 However, until the overall effects of I3C are better understood, we recommend obtaining this substance through consumption of broccoli family vegetables rather than taking it as a supplement. (See Safety Issues .)

Therapeutic Uses

I3C is being studied as a chemopreventive agent: a substance that helps prevent cancer . Numerous animal studies suggest that I3C might help reduce the risk of estrogen-sensitive cancers, as well as other types of cancer. 16-19,31-33 One double-blind, placebo-controlled study in humans suggests that it can help reverse cervical dysplasia , a precancerous condition. 20 Weaker evidence hints at benefits for vulvar intraepithelial neoplasia, a precancerous condition of the vulva. 37Note : Do not attempt to treat cervical dysplasia, or any other precancerous or cancerous condition, without physician supervision.

Some evidence indicates that I3C might also help prevent recurrences of a rare condition called respiratory papillomatosis. 21,34 This disease involves benign tumors in the lungs, mouth, and vocal chords.

I3C has additionally been investigated as a liver protectant . 22

Further evidence suggests that I3C must be exposed to stomach acid to exert its full effects. 11-15 For this reason, individuals with low stomach acid, such as those taking H 2 blockers (eg, ranitidine [Zantac]) or proton pump inhibitors (eg, omeprazole [Prilosec]), may not benefit as much from I3C.

What Is the Scientific Evidence for Indole-3-Carbinol?

A 12-week, placebo-controlled trial of 30 women with stage II or III cervical dysplasia found that treatment with I3C at a daily dose of 200 or 400 mg significantly improved the rate at which the cervix spontaneously returned to normal. 23

Safety Issues

Studies in rats, chickens, guinea pigs, mice, and dogs suggest that I3C is safe at recommended doses. 24 Human trials have found no significant side effects with I3C. 25,26,27

However, one study in rats found increased abnormalities in male offspring, specifically related to their fertility. 35 For this reason, I3C supplements should not be used by pregnant women.

There are other concerns with I3C, as well. For example, despite its overall anticancer effects, there is some evidence that I3C has tumor-promoting properties under certain circumstances. 28,29,36 For this reason, long-term use of concentrated I3C supplements may not be safe. In addition, individuals who have already had cancer shouldn’t use I3C (or any other supplement) except under physician supervision. (But you don’t need physician supervision to increase your broccoli intake!)

In addition, because it facilitates the inactivation of estrogen, it is possible that I3C might tend to promote osteoporosis in postmenopausal women and could interfere with estrogen therapies (such as birth control pills and hormone replacement therapy). However, this concern is purely theoretical at this time.

Interactions You Should Know About

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