Hyacinth bulbs contain toxic alkaloids similar to those in daffodils.
The bulbs are by far the most dangerous part; freshly cut flowers and water are less toxic but still problematic.
Hyacinth bulbs contain alkaloids (including narcissine) and calcium oxalate crystals. These cause intense oral irritation, severe vomiting and diarrhea, and at higher doses cardiac and respiratory effects. Skin contact with the bulbs can cause dermatitis in humans and dogs.
Sources
Ingestion of more than a single bulb in a medium dog can lead to severe vomiting and dehydration requiring IV fluids.
Contact your veterinarian or an emergency animal poison hotline immediately. Do not induce vomiting unless instructed by a vet.
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