Indole-3-carbinol (I3C): What it is and why people use it

Indole-3-carbinol, usually called I3C, is a compound your body makes when you chop or chew cruciferous vegetables like broccoli, cabbage, Brussels sprouts and cauliflower. It’s not stored in the veggies — it forms from a precursor called glucobrassicin when plant cells are damaged. People take I3C or its more stable breakdown product DIM as supplements for hormone balance, liver support, and cancer prevention claims.

Where it helps—and what the evidence actually shows

Most lab and animal studies show I3C affects estrogen metabolism and can slow growth of some cancer cells. That’s why you’ll see I3C mentioned in breast, prostate, and cervical cancer research. Human studies exist but are limited and often short-term. Some trials report improved markers linked to estrogen processing, but hard proof that I3C prevents or treats cancer in people is still lacking. Think of it as promising, not proven.

If you’re aiming for practical change, eating more raw or lightly cooked cruciferous vegetables is the easiest, safest bet. Cooking can reduce the enzyme (myrosinase) that starts I3C formation, but your gut bacteria can still convert the compounds, so both raw and cooked veggies help.

Dosage, safety and choosing a supplement

Typical supplement doses range from 100–400 mg of I3C per day; some people use DIM instead because it’s more stable and better absorbed. Short studies often used 200–400 mg. Long-term safety data are limited, so avoid very high doses unless a clinician recommends them for a specific reason.

Side effects are usually mild: stomach upset, nausea, headache or skin rash. I3C can change how your liver breaks down drugs and may interact with hormone therapies, birth control, or medications that rely on liver enzymes. If you’re on prescription meds, pregnant, breastfeeding, or have a hormone-sensitive condition, talk to your doctor before starting I3C.

When picking a supplement, choose brands with third-party testing, clear labeling, and no unnecessary fillers. Check whether the product lists I3C or DIM as the active ingredient and pick the one that matches your goals. If you want the whole-food route, aim for a few servings a week of varied cruciferous veggies instead of relying only on pills.

Bottom line: I3C is a natural compound with interesting effects on hormones and cell growth, but human evidence is still developing. Eat more cruciferous vegetables for a safe boost, and use supplements cautiously and with medical advice when needed.