Rhododendron poisoning

Medically Reviewed by Mahammad Juber, MD on December 16, 2022
5 min read

Rhododendrons produce beautiful displays of blooms, especially in the spring. The word "rhododendron" is a combination of the Greek words "rhodos" meaning "rose" and "dendron" meaning "tree." Most species are shrub-like, although some grow into trees. These much-loved plants also contain toxins, although they seldom pose a risk to humans.  

A simple way of classifying plants is by family, genus, and species. Rhododendrons belong to the heath family of plants, which also includes heather, blueberry, and cranberry. Rhododendron is the genus name, and the rhododendron genus contains around a thousand species.

In the United States, rhododendrons are mostly used in landscaping. People in other parts of the world have found other uses for this diverse group of plants. 

  • The people of Nepal use the leaves of one fragrant species to scent their temples. They also use the leaves to make essential oil
  • Larger species yield wood that can be used for eating utensils, furniture, fences, and firewood.
  • In Asia, people add the flowers of some species of Rhododendron to their food and drink.

Those who practice traditional or herbal medicine often use rhododendron plants, although all parts of the plant contain toxins. Early research shows that rhododendrons may have some medicinal uses. However, you should exercise caution or simply avoid using commercial products derived from rhododendron plants because their effectiveness has not been proven, and there are few controls on their manufacture and sale.

You should not make your own herbal medicines, according to poison control experts. You should not harvest plants in the wild or even from your own yard unless you know how to use them safely. Many plants are toxic in food and drinks.

Identifying a plant as a rhododendron can be tricky as the genus is so diverse. Rhododendrons can be a few inches tall, or they can grow into giant trees. The leaves vary widely in size and shape. Rhododendrons can be evergreen, or they can lose their leaves in the fall. The bark can differ in color and texture. The only reliable identifying mark is that the leaves grow in a spiral pattern around the stem.

When rhododendrons bloom, you have another way to identify them, as all rhododendron flowers have five lobes. They are bell- or funnel-shaped, and they come in a variety of colors, mostly white, pink, red, and purple, with some yellow and orange. 

Rhododendrons are native to most of the northern hemisphere and also to Asia and Australia. They don't occur naturally in Africa or South America. They have been widely cultivated as well, with plant lovers creating over 28,000 varieties. You are likely to encounter rhododendrons no matter where you live. 

If you live in the southern United States, you are probably familiar with azaleas. Azaleas belong to the rhododendron genus, although botanist Carl Linnaeus originally considered them to be their own genus. Most azaleas have a single flower to a stem, while other rhododendrons have clusters of flowers.  

Rhododendrons thrive in moist, acidic soil that is well-drained. Most varieties grow best where it is not too hot or too cold. Most bloom between March and May, but some bloom as early as January or as late as September. The species that lose their leaves often display lovely fall colors.

Rhododendron plants contain toxic substances called grayanotoxins that are harmful if eaten. Most poisoning cases occur when people eat honey from bees that feed on rhododendron nectar. There are accounts of ancient armies suffering defeat after eating "mad honey," which caused confusion, upset stomach, general weakness, and other symptoms. Modern times have seen a few cases of "mad honey" poisoning, most near the Mediterranean. 

Eating rhododendron leaves, nectar, or flowers can cause symptoms similar to those caused by eating rhododendron honey. Children sometimes put the leaves or flowers in their mouths, or try to suck the nectar from the blossoms. This small amount of exposure usually results in mild symptoms. 

No known fatalities have occurred from "mad honey" in recent times. The most dangerous scenario occurs when people purposefully take honey or supplements containing rhododendron. The concentration of toxins could be much higher in such products. You could have serious symptoms including cardiac and gastrointestinal problems if the concentration is high enough.

It's interesting that the toxins in rhododendron nectar don't hurt the bumblebees, their main pollinators. Other species of bees are sometimes affected. This may be the plant's way of favoring the pollinators that do the best job. The purpose of the toxins may be to discourage insects and other creatures from feeding on the plants.

The grayanotoxins in rhododendrons can cause a wide range of cardiovascular symptoms, including:

  • Hypotension (low blood pressure)
  • Atrial fibrillation (a fluttering heartbeat)
  • Bradycardia (an abnormally slow heartbeat)
  • Other problems with heart rhythm

Other symptoms that can occur include:

Livestock and other animals are at higher risk of rhododendron poisoning than humans. Horses, sheep, and goats may eat rhododendrons, especially during the winter when other food is scarce. Signs of toxicity may appear if they eat as little as two thousandths of their body weight. Digestive symptoms include:

  • Loss of appetite
  • Excessive salivation
  • Vomiting 
  • Colic (abdominal pain)
  • Diarrhea

Affected animals may also display weakness, poor coordination, stupor, and leg paralysis. The animal may be unable to stand for two days. At that point, the animal may improve or may enter a coma and die.

If you have symptoms associated with grayanotoxins, you should see your doctor. Grayanotoxin poisoning is usually diagnosed by taking a history of foods and natural remedies that you have ingested. 

Most of the time, rhododendron poisoning treatment is aimed at relieving the symptoms. You will usually feel better in a day, although it may take a few days for complete recovery. If your symptoms are severe, or if they include cardiac symptoms, your doctor may use saline infusions, a medication called atropine, or other treatments.

Plant identification is the key to avoiding toxic plants. You shouldn't eat any plant that you can't clearly identify. Unfortunately, the average person isn't a plant identification expert, and some poisonous plants look like food. Plant identification books and apps can help, but it's always better to err on the side of safety. 

There are many plants in the rhododendron family and many safe plants that look like rhododendron. Still, rhododendron poisoning is rare because most rhododendrons don't look like food. For example, Rhododendron maximum is highly toxic and possibly fatal if eaten. But it can grow up to 30 feet tall and has the largest leaves of any native rhododendron. It doesn't look like food.