Yes, bougainvillea plants are considered toxic to cats. The sap and thorns of the plant contain irritants that can cause skin irritation, inflammation, and gastrointestinal upset if ingested by cats. Common symptoms of bougainvillea poisoning in cats may include excessive drooling, vomiting, diarrhea, and possible difficulty swallowing. Keep cats away from bougainvillea plants to prevent potential harm and consult a veterinarian if signs of ingestion occur.