Find us on Social Media:

What is it? Overview Usage Side Effects and Warnings

Indole-3-Carbinol Side Effects and Warnings

Written by FoundHealth.

Safety Issues

Studies in rats, chickens, guinea pigs, mice, and dogs suggest that I3C is safe at recommended doses. 1 Human trials have found no significant side effects with I3C. 2 However, one study in rats found increased abnormalities in male offspring, specifically related to their fertility. 3 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. 4 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

If you are taking:

  • Any medication that contains estrogen (including birth control pills ): I3C might interfere with its action.


  1. Background information. Indole-3-carbinol (I3C). 700-06-1, June 28, 2000. National Institute of Environmental Health Sciences web site. Available at: Accessed September 19, 2000.
  2. Bell MC, Crowley-Nowick P, Bradlow HL, Sepkovic DW, Schmidt-Grimminger D, Howell P, Mayeaux EJ, Tucker A, Turbat-Herrera EA, Mathis JM. Placebo-controlled trial of indole-3-carbinol in the treatment of CIN. Gynecol Oncol. 78(2):123-9.
  3. Wilker C, Johnson L, Safe S. Effects of developmental exposure to indole-3-carbinol or 2,3,7,8-tetrachlorodibenzo-p-dioxin on reproductive potential of male rat offspring. Toxicol Appl Pharmacol. 1996; 141:68-75.
  4. Dashwood RH. Indole-3-carbinol: anticarcinogen or tumor promoter in brassica vegetables? Chem Biol Interact. 1998;110:1-5.


No one has made any comments yet. Be the first!

Your Comment