What Is Indole-3-Carbinol?

Indole-3-carbinol (IC3) is a substance that the body produces when it breaks down glucobrassicin. Where do you find glucobrassicin? It’s a compound found naturally in cruciferous vegetables like cauliflower and broccoli.

You can also find IC3 sold in supplement form. You may have heard claims that indole-3-carbinol fights cancer, which is the primary reason most people have for taking the supplement.

Unfortunately, the claims about its cancer-fighting qualities are primarily based on animal studies. There’s very little conclusive evidence that taking indole-3-carbinol will magically prevent or cure cancer. Some of the research is promising, but we definitely don’t know enough to make any specific conclusions. 

Person making a healthy green salad
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What Is Indole-3-Carbinol Used For?

The central claim about indole-3-carbinol is that it may help prevent certain cancers. However, that doesn't mean you should use it to treat cancer after you have been diagnosed. What does the research say about the health benefits of IC3? 

Cancer Prevention

Animal studies show that diets high in cruciferous vegetables can slow cancer growth. Lab studies also suggest that I3C may improve the effectiveness of chemotherapy treatments.

Unfortunately, there isn't a lot of data on its effects in humans. In one clinical trial, I3C did clear cervical intraepithelial neoplasia (CIN) and prevent the progression of precancerous cells in people with abnormal Pap smears, a test done to screen for cervical cancer. There’s also some evidence that I3C has the opposite effect. Some animal studies have shown I3C promoting tumor growth.

In early clinical trials, evidence suggests that I3C may reduce female breast cancer risk in some people and help eliminate precancerous cervical cells caused by the human papillomavirus (HPV). That said, the results of such studies have been mixed.

Systemic Lupus Erythematosus (SLE)

Again, the evidence concerning i3C for the treatment of systemic lupus erythematosus is limited. In animals, the supplement reduced kidney disease and prolonged life, but no symptom improvements were noted in human females.

Viral infections

Some research also suggests that I3C may have antiviral effects, but this info is based solely on lab research.

Possible Side Effects 

There isn’t much research specific to humans, but lab studies have shown that I3C may interact with certain drugs such as cytochrome P450 1A2 substrate drugs. These drugs include Clozaril (clozapine) and Cymbalta (duloxetine). Always talk to your healthcare provider before taking a supplement.

Supplements are easy to purchase, but they can also have unexpected side effects. Most people who take the supplement tolerate it reasonably well. However, I3C may cause skin irritation in some people. 

It’s not totally clear whether the potential benefits outweigh the risks of taking I3C. If you already eat many cruciferous vegetables, it may not even be worth it to supplement with I3C. Research says that high doses of I3C may not be more effective than smaller ones.

One older study found that I3C may cause tremors in high doses, but the symptoms should go away when the dose is lowered. Some women who participated in an I3C study for breast cancer reported having gastrointestinal issues when taking doses of up to 600 milligrams (mg).

Some studies show that the supplement may increase the risk of developing cancer, suggesting that a cautious approach towards I3C is the best one. Another study from 2015 also notes the potential for I3C to cause toxic effects. However, these conclusions are not based on human findings.

Dosage and Preparation

No specific safe dosage has been determined for humans. However, supplement companies suggest varying dosages between 200 to 800 mg per day. In human studies, doses were generally between 200 to 400 mg per day.

What to Look For 

When shopping for any supplement, always buy from reputable brands and avoid companies that make sweeping claims about their products. 

If you’re thinking of taking I3C, you may want to first try increasing the amount of cruciferous vegetables in your diet. Consider that there’s no definitive research about the safety or health benefits of I3C. There’s just not enough research to say for sure whether it’s entirely safe to take I3C and whether it really does have anticancer effects.

Other Questions

What foods contain glucobrassicin?

Vegetables other than broccoli and cauliflower that contain glucobrassicin include:

  • Brussels sprouts
  • Kale
  • Cabbage 
  • Kohlrabi
  • Collards
  • Mustard greens
  • Rutabaga
  • Turnip

Can I3C affect blood pressure?

Some animal studies suggest that I3C may cause high blood pressure. 

A Word From Verywell 

While what we know so far about I3C is promising, more research is needed to confirm the supplement’s health benefits. Research is also needed to better understand any potential risks of supplementing with I3C.

If the cancer-fighting benefits appeal to you, consider supplementing your diet with more broccoli, kale, and Brussels sprouts. If you really want to try supplementing with I3C, talk to your healthcare provider before doing so. 

9 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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  5. Reed G A, Arneson D W, Putnam W C, et al. Single-dose and multiple-dose administration of indole-3-carbinol to women: pharmacokinetics based on 3,3'-diindolylmethaneCancer Epidemiol Biomarkers Prev. 2006;15(12):2477-2481. doi:10.1158/1055-9965.EPI-06-0396

  6. Dashwood R H. Indole-3-carbinol: anticarcinogen or tumor promoter in brassica vegetables?Chem Biol Interact. 1998;110(1-2):1-5. doi:10.1016/s0009-2797(97)00115-4

  7. Fletcher A, et al. Reversible toxic effects of the dietary supplement indole-3-carbinol in an immune compromised rodent model: Intestine as the main targetJ Diet Suppl. 2017;14(3):303-332. doi: 10.1080/19390211.2016.1215367

  8. Howard CG, Mullins JJ, Mitchell KD. Transient induction of ANG II-dependent malignant hypertension causes sustained elevation of blood pressure and augmentation of the pressor response to ANG II in CYP1A1-REN2 transgenic rats. Am J Med Sci. 2010 Jun;339(6):543-8. doi:10.1097/MAJ.0b013e3181d82a62

By Steph Coelho
Steph Coelho is a freelance health writer, web producer, and editor based in Montreal. She specializes in covering general wellness and chronic illness.