Indole-3-carbinol (I3C) is a phytochemical (plant chemical) found in significant quantities in cruciferous vegetables (cabbage, broccoli, cauliflower, Brussels sprouts, kale, collards, kohlrabi). Capsules of I3C may be purchased without prescription as a nutritional supplement. This compound alters estrogen metabolism and the result is anti-proliferative. I3C has been widely used as a treatment for recurrent respiratory papillomatosis (RRP), though our physicians have found the benefit in their adult patients to be underwhelming.