AboutDoggies states that poppy seeds are toxic to dogs. It references the Pet Poison Helpline’s statement that any part of the poppy plant contains opioids that could cause mild to moderate adverse symptoms in a dog.
The Pet Poison Helpline states that poppy seed consumption could cause a sedative effect in dogs that could place the dog into a coma. Ingesting the seeds could cause other dangerous symptoms such as a loss of appetite, walking as if intoxicated, pinpoint pupils, and a slowed breathing and heart rate.
AboutDoggies recommends taking a dog to a veterinarian immediately or forcing the dog to vomit immediately after it ingests poppy seeds.