Some coleus plants are toxic to cats, as well as dogs and horses. The plants contain an essential oil that can cause moderate to severe digestive problems when consumed.
Cats who eat toxic coleus plants can experience diarrhea and vomiting. In severe poisoning, the vomit and diarrhea may contain blood. The cat may also lose his appetite and become depressed or lethargic. The many varieties of coleus are divided into two genera. Chemical properties vary between species, so the amount needed to poison a cat may change significantly according to which plant he ate. Any cat that has eaten leaves or stems from a coleus plant should receive a veterinary evaluation, even if he has no immediate symptoms.