Yes, Narcissus is toxic to dogs!
Dogs accidentally consuming the Narcissus plants can show the following clinical symptoms: Vomiting, Prolonged Depression, Incoordination, Hypersalivaton, Sleepiness Or Excitation, Dilated Pupils, Low Body Temperature, Low Blood Pressure, Coma, Seizure And Death (In Rare Cases).
Narcissus consumption is also toxic to Cats and Horses.
Toxic Principles Of Narcissus: Lycorine and other alkaloids.
More Info About The Narcissus Plant
Scientific Name: Narcissus spp
Family: Amaryllidaceae.
Also known as: Daffodil, Jonquil, Paper White.
The answer is based on information found on The American Society for the Prevention of Cruelty to Animals (ASPCA) website.