Indole-3-Carbinol (I3C): What It Is and Why People Use It

Indole-3-carbinol (I3C) is a plant compound found in cruciferous vegetables like broccoli, Brussels sprouts, cabbage, and kale. When you chew these vegetables, I3C forms and then partly converts in your stomach to other compounds, including diindolylmethane (DIM). People take I3C supplements mainly to support healthy hormone balance and antioxidant activity.

I3C isn't a miracle cure, but it has clear biological effects on how the body processes estrogen and other hormones. That’s why some researchers looked at it for conditions linked to estrogen, such as benign breast changes and cervical cell changes. Human studies are limited, but a few clinical trials reported modest benefits in specific situations. Always view supplements as one tool, not a replacement for medical care.

Common Uses and Typical Doses

People use I3C for: supporting estrogen metabolism, balancing hormones during perimenopause, and as an antioxidant support. Typical supplement doses range from 200 mg to 400 mg per day. Some protocols use split dosing or start low and increase over weeks. DIM supplements are another option—because I3C partly converts to DIM, some prefer DIM for more predictable effects and fewer stomach issues.

Safety, Side Effects, and Interactions

Side effects are usually mild: stomach upset, headache, and sometimes a change in urine odor. I3C can change liver enzymes and affect how some drugs are broken down. That means it may alter the effectiveness of medications processed by the liver, especially hormone therapies, birth control pills, and certain cancer drugs. If you are pregnant, breastfeeding, have a hormone-sensitive cancer, or take prescription meds, check with your doctor before using I3C.

Avoid very high doses without medical supervision. Long-term safety data are limited. If you notice new symptoms after starting I3C—worse digestion, mood shifts, or unexpected bleeding—stop and talk to a clinician.

When choosing a supplement, look for third-party testing (USP, NSF, or similar), clear labeling of I3C amount per dose, and reputable manufacturers. Decide whether you want I3C or DIM based on tolerance and goals; DIM tends to be more stable and easier to dose for estrogen support.

Quick tips: get some cruciferous vegetables in your diet first—they provide I3C naturally. Use supplements only when needed, follow suggested doses, and pair changes with lab checks if you’re managing hormones or taking medications. If you’re unsure how I3C fits your health plan, a short chat with your healthcare provider will save time and reduce risk.