Azalea and Rhododendron Poisoning

Filed Under: Dogs, Cats, Horses, Cows, Poisoning

The beautiful flowering shrub adjacent to your porch may have a sinister side to it. Don’t let those colorful blooms fool you. Cuttings from these bushes may be toxic to your pets and livestock.

Azaleas and rhododendrons are members of the plant family Ericaceae, a group of garden shrubs that contain the toxin andromedotoxin which is a cardiac glycoside. Some rhododendrons will have an additional toxin called grayanotoxin in their pollen and nectar. Animals must consume these plants in rather large amounts, equivalent to 0.2% of their body weight for clinical signs of poisoning to develop. Livestock grazing near recently trimmed bushes are the most likely to show clinical signs of toxicosis. Even people have become ill from honey made by bees feeding on these plants.

Clinical signs typically develop within six hours following ingestion and reflect damage to the gastrointestinal tract and the heart. Livestock will be anorexic, salivate, be depressed, repeatedly swallow, and show general signs of nausea, projectile vomiting, ataxia, epiphora, paralysis of the limbs, stupor, bradycardia (slow heart rate) followed by tachycardia (rapid heart rate) later in the syndrome, heart block, coma, and death. In horses, the consumption of clippings will often lead to colic, tenesmus, and grinding of the teeth. Defecation may increase in frequency but seldom is diarrhea a prominent clinical sign. Animals surviving more than 2 days usually recover, but deaths have occurred as long as 14 days following ingestion.

When caught early, activated charcoal lavage may be used to prevent absorption followed by a saline cathartic to cause bowel evacuation. Additional treatment is symptomatic and is directed toward providing for the animal’s fluid needs and keeping their electrolytes balanced.


Fowler, Murray. Plant Poisoning in Small Companion Animals. Ralston Purina Co. 1981. P. 7.

Gupta, Ramesh Editor. Veterinary Toxicology. Elsevier. 2007. Pp. 197 and 201-202

Kahn, Cynthia. The Merck Veterinary Manual. Merck and Co. 2005. Pp. 2440-2441.

Smith, Bradford. Large Animal Internal Medicine. 2nd Edition. Mosby. 1996. P. 1881-1882.

Topics: flowers, plants, poisoning

Symptoms: nausea, paralysis, salivation, vomiting

Similar entries

  • Oleander is an ornamental shrub that flowers in various colors including white, red, pink and violet. This plant is an evergreen perennial that flowers throughout the summer months. Originally a native plant of the Mediterranean, oleander is a very drought-tolerant ornamental. Oleander is now commonly found in warmer areas of the United States. It is often planted as an ornamental hedge along roads and gardens, although it is occasionally grown as a houseplant. The leaves are thick and leathery and vary from four to twelve inches in length.

  • The castor bean plant (Ricinus communis) or palma christi is a common ornamental houseplant with large, palmated, lobed leaves that may be found in almost any location in the United States. The plant is also grown for the manufacturing of castor oil. This same plant has a more sinister side and may be used to produce a potent phytotoxin called ricin.

  • Thinking of throwing out that poinsettia the florist just delivered since you have pets in the house? That is probably not necessary. Although poinsettia poisoning has gained a lot of press, they are not all that toxic.

    Poinsettias (Euphorbia pulcherrima) are also known as the "Christmas flower" or "star". They are a popular plant used as decoration around the holidays from November through December. The plant is actually a shrub and has brightly colored red, white or pink terminal leaves while the lower leaves remain green in color.

  • Did you know that cockleburs (Xanthium genus), those annoying burs that stick to your clothes and scratch your skin, are toxic if consumed?  Most people are not in the habit of consuming the prickly, spiny seed pods, but they can be incorporated into animal feeds and hay.  Horses, pigs, and cattle can all become poisoned.  Pigs are the species most commonly poisoned from these seedlings.  

  • Raising avocados may be detrimental to the health of your horse. Avocado leaves, fruit, bark, and seeds all contain persin and an unidentified cardiac toxin. In lactating mares, persin produces a non-infectious mastitis (inflammation of the mammary glands), epithelial necrosis (skin cell death over the mammary glands) and agalactia (decrease in milk production). Occasionally gastritis and colic may occur.