Verdict: In moderation
Broccoli is generally considered safe for cats in very small, infrequent amounts. However, large quantities can cause gastrointestinal upset due to compounds called isothiocyanates. If your cat consumes a significant amount and shows signs of vomiting or diarrhea, contact your veterinarian.
While generally safe in small amounts, large quantities of broccoli contain isothiocyanates which can cause mild to moderate gastrointestinal irritation.
Isothiocyanates