These flowers contain grayanotoxin, a toxin that can cause gastrointestinal issues, weakness, paralysis, and abnormal heart rhythms.
Source: Chewy Editorial, 2020.
It's so common for dogs to be in contact with these plants that finding articles about them isn't difficult at all. You can read more about the symptoms, diagnosis, and treatment at the Wag website: https://wagwalking.com/condition/rhododendron-poisoning
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