According to the ASPCA, eucalyptus is toxic to dogs as well as to cats and horses. The dangerous component is the oil of the plant. Dogs that ingest toxic amounts of eucalyptus exhibit symptoms that include salivation, vomiting, diarrhea, depression and weakness.
The ASPCA advises contacting a veterinarian if a dog has eaten eucalyptus. PetMeds emphasizes that house and garden plants are often problematic for pets. One-quarter of pets that are poisoned by something other than medications are sickened by plants. Pet owners need to discourage their pets from interacting with plants, and they need to poison-proof their homes for pets in the same manner they use to protect young children.