Indole-3-Carbinol (I3C) Supplementation: Benefits, Side Effects & Dosage

Indole-3-Carbinol (I3C) is a derivative of glucobrassicin, a type of glucosinolate that can be found in cruciferous vegetables such as cabbages, broccoli, and mustards [i]. In mammalian stomachs, I3C molecules undergo a type of condensation that is catalyzed by strong acids and that generates a number of biologically active components. The most active I3C oligomers (this refers simply to a relatively simple polymer with few repeating units) include 3,3’-diindolylmethane (DIM) and 5,11-dihydroindolo-[3,2-b]carbazole (ICZ) [ii].

Numerous clinical and preclinical studies have strongly indicated that I3C and its oligomers have anti-estrogenic activity. As a result, there has been significant interest in the medical community in exploring the ways in which I3C might help reduce tumorigenesis in hormone-dependent cancers. Some more limited evidence from preliminary trials also points to I3C supplementation as possibly effective in the treatment of conditions related to human papillomavirus (HPV) infection, such as cervical/vulvar intraepithelial neoplasias and recurrent respiratory papillomatosis [v]. Other benefits of I3C supplementation are described in greater detail below, though it is important to note that further clinical research is needed to evaluate I3C’s efficacy in relationship to other hypothesized therapeutic effects such as weight loss and lean muscle growth [vi].

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I3C vs DIM

Both I3C and DIM have been observed to modulate the expression of biotransformation enzymes that regulate or are involved in the metabolism and elimination of a variety of biological compounds, which may include steroid hormones, carcinogens, and other harmful toxins [iii]. However, I3C and DIM are not precisely the same.

One of the main differences relates to the stability of these molecules. I3C is relatively unstable; in other words, it does not maintain its original structure for very long and rapidly converts to DIM and other substances in the stomach. DIM, on the other hand, is a more stable molecule. Whether converted from I3C or taken as a supplement, DIM progresses beyond the stomach as an active molecule in the body. With that being said, in terms of dietary supplementation, the benefits of both are quite similar, likely owing to the high rate at which I3C converts into DIM. However, DIM tends to be the preferred supplemental form simply because it a stronger component; the body does not have to complete as many conversion steps to receive its benefits [iv].

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Benefits of I3C


In a study published by Anticancer Research, researchers explored the anti-estrogenic activities of I3C in HPV-infected cervical cells, with the aim of preventing cancerous proliferation. More specifically, they measured estrogen metabolites and explored the impact of I3C and 2-hydroxyestrone (2-OHE) in the cervical cell cancer cell line CaSki (HPV type 16). They found that I3C enhanced the gene expression of enzymes responsible for 2-hydroxylation of estrogen and competed with estradiol (a hormonal drug utilized to treat menopausal symptoms as well as breast cancer) for estrogen receptor binding. Put more simply, I3C was found to have anti-estrogenic activities, which could prevent cancer in HPV-infected cervical cells [vii].

Another study published by Cancer Research affirmed similar results. Researchers compared the impact of I3C supplementation on transgenic mice. One group was fed a control diet at a dose of estradiol of 0.125 mg per 60-day release, and the other was fed I3C. In the control diet, 19 of 25 mice developed cervical cancer within 6 months. In contrast, only 2 out of 24 mice in the I3C group developed cervical cancer. Researchers concluded that I3C may be a useful preventative for cervical cancer and possibly other cancers with a papillomavirus component [viii].


A study published by Anticancer Agents in Medical Chemistry investigated I3C-derived CTet as a chemopreventative agent in MCF-7/AROM-1 breast cancer cells. Specifically, they evaluated testosterone (TE) aromatization and proliferation, Rα phosphorylation/activation and Bcl-2 and IGF-1R ERE-regulated protein accumulation in estradiol. Results indicated that CTet inhibited TE-driven ERα phosphorylation, in turn implying an inhibitory effect of TE aromatization in estradio. Finally, CTet and letrozole, a nonsteroidal aromatase inhibitor used to treat breast cancer, collectively inhibited TE-induced cell proliferation. All of these observations led researchers to conclude that I3C-derived CTet may be effective as a chemopreventative agent in hormonal cancers, particularly in light of its TE-regulatory activity [ix].


It is hypothesized that some of the characteristics of I3C may support athletic performance and muscle growth. Advocates of I3C supplementation maintain that it helps increase lean muscle mass and burn fat stores. Concurrently, many of those same advocates have conjectured that I3C might serve as a safe alternative to steroids based on its hormone-regulating properties. However, no clinical research studies examining the effect of I3C or DIM on bodybuilding have been conducted to date, so this information is strictly anecdotal. Further, no evidence indicates that I3C increases testosterone levels in healthy patients [x].

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Pancreatic Cancer

Due to its aggressive characteristics, pancreatic cancer is often fatal. Pancreatic cancer is the fourth leading cause of death in the United States. Fortunately, there is some clinical indication that I3C may have chemopreventative and/or therapeutic qualities in the treatment of pancreatic cancers. For example, in a study published by Cellular and Molecular Biology, researchers treated pancreatic cancer cells (MIA PaCa-2) with 1, 10, or 100 mM of I3C. Methylated-sensitive PCR (MSP) analyses demonstrated that I3C unmethylated the promoter region of the p16 protein (a multiple-tumor suppressor), and significantly decreased the expression of DNA methyltransferases. These data indicate that I3C may have therapeutic potential in terms of regulating the hypomethylation of pancreatic cancer cells [xi].

A study published by Anticancer Research yielded similarly constructive results. Researchers evaluated the change of chemosensitivity to gemcitabine, a nucleoside metabolic inhibitor, through the down regulation of miR-21 in human pancreatic cells (Panc-1). Results were positive, indicating that I3C may demonstrate efficacy in enhancing the sensitivity of pancreatic cancer cells to gemcitabine via the miR-21 pathway [xii].


Do not mess around with Cancer. While studies sometimes look promising, there is a lot more than meets the eye. Listen to your Oncologist.

Weight Loss

A study published by The Journal of Nutritional Biochemistry assessed the protective effect of I3C against diet-related obesity in transgenic mice. Laboratory mice were grouped together to receive a normal diet, a high-fat diet, or an I3C-supplemented diet for 10 weeks. Researchers found that I3C slightly ameliorated diet-induced increases in overall weight gain, visceral fat pad weights, and plasma lipid levels. These findings suggest that I3C may have a preventative effect in relation to obesity and metabolic disorders [xiii].

Indeed, many individuals invested in I3C or DIM supplementation are interested in these compounds as potential weight loss therapeutics, but more clinical research is needed to affirm their efficacy.

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Abundant research has indicated that I3C and DIM are both negative regulators of estrogen. For example, in a study published by Nutrition and Cancer, researchers indicated the strong association between short-term oral exposure to dietary I3C and estrogen metabolism in both men and women [xiv]. Studies such as these and many others have signified to researchers that I3C and DIM may be effective hormonal modulators in the treatment of estrogenic issues such as gynecomastia, or enlargement of the breast tissue in males. However, no clinical trials have been conducted to specifically measure the therapeutic impact of I3C or DIM on patients with gynecomastia. In other words, all research to this effect has been anecdotal and/or hypothetical [xv].


There has been one clinical study published by Kent State University that has examined the effect of I3C supplementation on herpes simplex virus (HSV). In this study, Vero cells (monkey kidney) and MRC-5 cells (human lung fibroblast) were treated with noncytotoxic concentrations of 267µM and 375µM of I3C each. Cells were then infected with HSV-1, HSV-2, or acyclovir resistant HSV-1 and viral yields were assayed. Replication of all HSV types was inhibited by at least 99.9% with I3C supplementation. These results indicate strongly that I3C has significant anti-HSV properties in vitro [xvi].


An abundance of clinical research indicates that I3C is a negative regulator of estrogen. Many of these studies were conducted with the long-range goal of figuring out how to best use I3C together with other nutrients to achieve maximum benefits for cancer prevention. For example, in a study published by The Journal of Nutrition, researchers observed a synergistic effect of I3C and genistein, a naturally occurring isoflavone, in the induction of growth arrest in response to DNA damage (or GADD) expression, thus increasing apoptosis. Concurrently, I3C was found to ameliorate the effect of estrogen in the proliferation of breast, endometrial, and cervical cancer-related tumors [xvii].

Another study published by the Journal of the National Cancer Institute yielded similar results. Researchers examined the dietary indoles of cruciferous vegetables in female rats in terms of the induction of hepatic estradiol 2-hydroxylation. I3C, the most potent indole, was later also administered to humans (500 mg daily for 1 week). Results yielded that supplementation significantly increased the extent of estradiol 2-hydroxylation in rats and humans, indicating that I3C strongly influences estrogen metabolism and may serve as a chemopreventative agent in relationship to estrogen-dependent diseases [xviii].


The appropriate dosage of I3C is dependent on several factors, including the age and overall health of the patient. Though there is an abundance of clinical information indicating I3C and DIM’s therapeutic potential, there is not enough scientific information specifically determining appropriate dosage ranges for supplementation. With this being said, individuals interested in supplementing with I3C and/or DIM should only do so under proper medical supervision and advice [xix].

Side Effects

Gastrointestinal distress (nausea and diarrhea), tremors, and skin rashes have been reported with very high levels of I3C and/or DIM supplementation (400 mg and up). There is not enough information to indicate if pregnant or breastfeeding individuals are safe to use I3C or DIM, so it is better to avoid use until more clinical trials are conducted to this effect. Further, IC3 and DIM are contraindicated in individuals with blood-related disorders or who have recently had surgery, as these supplements may slow blood clotting and thus increase the risk of bleeding [xx].

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[i] Chamovitz D.A., Katz E. & S. Nisani (2018) Indole-3-Carbinol: A Plant Hormone Combatting Cancer. F1000Research, 7: F1000 Faculty Rev-689.

[ii] Rogan E.G. (2006) The Natural Chemopreventative Compound Indole-3-Carbinol: State of the Science. In Vivo, 20(2): 221-228.

[iii] Murray M.T. & A. Sadlon (2020) Cervical Dysplasia. In: J.E. Pizzorno & M.T. Murray (Eds.), Textbook of Natural Medicine (Fifth Edition). London: Churchill Livingstone.

[iv] Diindolylmethane (DIM) Information Resource Center (n.d.) University of California Berkeley.

[v] Auborn K.J. (2006) Can Indole-3-Carbinol-Induced Changes in Cervical Intraepithelial Neoplasia be Extrapolated to Other Components? The Journal of Nutrition, 136 (10): 2676S-2678S.

[vi] Dean W. (n.d.) Chrysin: Is it an Effective Aromatase Inhibitor? Ward Dean, MD.

[vii] Auborn K., Chen D.Z., Bradlow H.L., Sepkovic D.W. & F. Yuan (1999) Anti-Estrogenic Activities of Indole-3-Carbinol in Cervical Cells: Implication for Prevention of Cervical Cancer. Anticancer Research, 19(3A): 1673-1680.

[viii] Anderson A., Arbeit J.M., Auborn K.J., Chen D.Z., Liang J. & G.Y. Yang (1999) Indole 3-Carbinol Prevents Cervical Cancer in Human Papillomavirus Type 16 (HPV16) Transgenic Mice. Cancer Research, 59(16).

[ix] Brandi G., Carloni E., De Santi M., Diotallevi A., Galluzzi L., et al. (2015) Inhibition of Testosterone Aromatization by the Indole-3-Carbinol Derivative CTet in CYP19A1-overexpressing MCF-7 Breast Cancer Cells. Anticancer Agents in Medical Chemistry, 15(7): 864-904.

[x] Brown G.A., King D.S., Parsons K.A., Reifenrath A., Sharp R.L. & N.L. Uhl (2000) Effects of Anabolic Precursors on Serum Testosterone Concentrations and Adaptations to Resistance Training in Young Men. International Journal of Sport Nutrition and Exercise Metabolism, 10(30: 340-359.

[xi] Haefele A., Hammons G. & B. Lyn-Cook (2008) Indole-3-Carbinol (I3C) Reactives P16 in Pancreatic Cancer Cells Through Hypomethylation. Cellular and Molecular Biology, 68(9).

[xii] Hwang J.H., Kim H.R., Lee S.H., Paik W.H. & B.J. Song (2013) Chemosensitivity Induced by Down-Regulation of MicroRNA-21 in Gemcitabine-resistant Pancreatic Cancer Cells by Indole-3-Carbinol. Anticancer Research, 33(4): 1473-1481.

[xiii] Choi Y., Kim Y., Lee K.W., Park S. & T. Park (2012) Indole-3-Carbinol Prevents Diet-Induced Obesity Through Modulation of Multiple Genes Related to Adipogenesis, Thermogenesis, or Inflammation in the Visceral Adipose Tissue of Mice. Journal of Nutritional Biochemistry, 23(12): 1732-1739.

[xiv] Bradlow H.L. & J.J. Michnovicz (1991) Altered Estrogen Metabolism and Excretion in Humans Following Consumption of Indole-3-Carbinol. Nutrition and Cancer, 16(1): 59-66.

[xv] Indole-3-Carbinol (2000, June 28) National Cancer Institute.

[xvi] Stoner T.D. (2011) Indole-3-Carbinol Inhibition of Herpes Simplex Virus Replication [Doctoral Dissertation, Kent State University].

[xvii] Auborn K.J., Carter T.H., Chandraskaren A., Chen D., Goodwin L., Fan S. & D.E. Williams (2003) Indole-3-Carbinol is a Negative Regulator of Estrogen. Journal of Nutrition, 133(7): 2470S-2475S.

[xviii] Bradlow H.L. & J.J. Michnovicz (1990) Induction of Estradiol Metabolism by Dietary Indole-3-Carbinol in Humans. JNCI: Journal of the National Cancer Institute, 82(11): 947-949.

[xix] Indole-3-Carbinol (2021, January 1) Linus Pauling Institute.

[xx] Indole-3-Carbinol (n.d.) WebMD.

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