Yes, the Lipstick Plant is poisonous to cats. The Lipstick Plant contains cardiac glycosides, which are toxins that can affect a cat's heart. If a cat consumes any part of a Lipstick Plant, they may experience symptoms such as vomiting, diarrhea, increased heart rate, and difficulty breathing. If you think your cat has ingested a Lipstick Plant, please contact your veterinarian immediately.