Rhododendrons belong to a large genus of flowering plants that includes both rhododendron bushes and azaleas. Numerous species and hybrid cultivars are grown as ornamental garden flowers, while others are found in the wild. All of these plants contain grayanotoxins (formerly called andromedotoxins) in varying levels. These diterpenoid compounds can disrupt metabolism at a cellular level and interfere with the normal function of nerves and muscles, particularly the heart. They are toxic to dogs as well as humans.

The leaves are the most poisonous part of the rhododendron plant, but the flowers and nectar can also be dangerous. Honey made from rhododendron nectar has been the most significant source of toxicity for humans, dating all the way back to a well-known case of Greek soldiers being poisoned by contaminated honey in 4th century B.C.E. Modern instances associated with non-commercial honey consumption have been documented in Turkey. Poisoning from rhododendron honey is called honey intoxication or mad honey disease; it produces dizziness, weakness, nausea and vomiting with more severe symptoms and death possible at higher doses. 

Dogs are less likely to be poisoned by eating honey, but chewing flowers and leaves from a garden bush can be more of a problem. Toxic and lethal symptoms have been seen with doses as low as 3 milliliters per kilogram of body weight for flower nectar, and .2 % of body weight with leaves. Excessive salivation and vomiting within 6 hours of ingestion are usually the first signs, but these may be followed by weakness, inability to stand, vision loss and abnormal heart rhythms. In fatal cases, death usually occurs in 1-2 days. Veterinary treatment can ameliorate the symptoms and increase the dog’s chances of survival.

All parts of the rhododendron plant are toxic for dogs. Symptoms include gastrointestinal upset followed by weakness, paralysis, and abnormal heart rhythms. Large doses can be fatal.

Look for these symptoms if your dog eats rhododendron.

Some species of rhododendron contain higher levels of grayanotoxins than others, however with hybridized garden species it’s safer to assume all varieties could be toxic. These are some of the species known to be associated with toxic honey.

These are some causes and risk factors for rhododendron poisoning.

If you know your dog has eaten leaves or flowers from a rhododendron bush, it’s best to call a veterinarian or a poison helpline. Some dogs do regularly consume a small amount of rhododendron leaves without developing symptoms, but this depends a lot on the specific variety of rhododendron as well as the size of your dog. Emergency veterinary treatment is needed immediately if symptoms are severe.

Diagnosis is based on a history of ingestion as well as symptoms. Vomiting and gastrointestinal upset are non-specific signs of toxicity, but combined with an abnormally slow heart rhythm, and atrioventricular block, this could suggest grayanotoxin toxicity. The veterinarian will physically examine your dog and listen to his heart. Unusual rhythms will be further analyzed using an echocardiogram or an electrocardiogram. Blood tests may also show electrolyte abnormalities. If you aren’t sure what happened, other possible causes will need to be eliminated.

For initial treatment, remove any un-swallowed plant material from the mouth, and rinse with water or milk. Encourage your dog to drink fluids to dilute the toxin. Don’t induce vomiting unless recommended by a veterinarian or a professional poison expert. Immediate veterinary treatment is advisable, especially if a large amount was ingested.

For recent poisoning, the veterinarian will induce emesis. Activated charcoal will be given throughout the first day. This medication will bind to the toxins in your dog’s stomach and reduce further absorption.

Other treatment will focus on the symptoms. Intravenous fluids and additional oxygen may be administered. If bradycardia (slow heart rhythm) is very severe, atropine will likely be prescribed. Quinidine may be given for heart block. If a temporary pacemaker is available for dogs, this can help stabilize the heart until the toxins are excreted. Most symptoms resolve themselves in 24 to 48 hours. For cases of severe poisoning, your dog will need to stay in a veterinary hospital during that time.

Serious rhododendron poisoning is rare since dogs don’t typically eat large amounts of plant material. Most dogs will make a complete recovery, especially with prompt veterinary treatment. The size of your dog, the amount that was ingested, and the toxicity level in the plant will all be relevant. A veterinarian will be able to better evaluate your dog’s chances upon diagnosis.

To manage the condition, try to discourage your dog from chewing on garden bushes and flowers. If your dog is prone to snacking on green material, try growing grasses that can be consumed safely and interest him in eating these instead of toxic plants. If rhododendron poisoning is a recurrent problem, consider eliminating the bush and plant something else that will be less toxic for your dog.

Rhododendron poisoning in dogs can be expensive to treat. If you suspect your dog is at risk of being poisoned by a toxic plant, start searching for pet insurance today. Wag!’s pet insurance comparison tool lets you compare plans from leading companies like PetPlan and Embrace. Find the “pawfect” plan for your pet in just a few clicks!