The Rhododendron sub-family of Ericaceae covering all Rhododendrons and Azaleas are one of many plant families to contain glycosides; a vast collection of monosaccharide-derived compounds, some of which are potenially toxic. The principal glycoside toxin or grayanotoxin present in all Rhododendrons and Azaleas (one of several) is "Andromedotoxin" (other names including rhodotoxin and acetylandrome). Chemically similar to components of turpentine such as pinene, and like turpentine, this volatile resin burns the mouth and hence is a deterant to many herbivores and young children. Fortunately, the human digestive system can break down andromedotoxins into harmless compounds. However, consumption of enough foilage (especially the leaves), berries of flowers can give symptoms of vomiting and stomach upset, very reduced blood pressure and nausea six hours afterwards. There may also be loss of coordination and weakness in the muscles.
Deaths have occurred from excessive consumption of particularily the honey produced by bees from the flowers and the nectar. Indeed, the bees are often poisoned. Poisoning from this often called "honey intoxication", "grayanotoxin poisoning", "mad hone intoxication" or "Rhododendron poisoning", and the symptoms are the same as before for both animals and humans. The effects of "honey intoxification" have been known since 400BCE. Animals suffer the same symptoms and indeed may be more susceptible. Common culprits include Cherry Laurel (Prunus laurocerasus) (strictly from the family Rosaceae), Mountain Laurel (Kalmia latifolia), cultivated Rhododendrons and house or garden Azaleas. The plant named "Lambkill" or Sheep's Laurel (Kalmia augusfifolia) certainly indicate the poisoning potential of these plants. Here are some pictures illustrating the collection of plants, 1, 2 and 3.
Some of the mentioned species may also contain the toxic glycoside, "Arbutin" also present mainly in the Rose family (Rosaceae).