Indole-3-carbinol's cancer-preventive or promoting effects depend on timing relative to carcinogen exposure.

“These compounds have gotten sort of a mixed review from a health perspective because it's been shown they can polymerize or form dimers or tetramers that actually resemble dioxin, the potent toxin. And so in animal studies, now I haven't updated my brain on this for a number of years, but when I last did about four, five years ago, there were an equivalent number of animal studies showing a cancer-preventive effect of indole carbinol, I3C, to those which showed that it actually promoted cancer.”