For centuries, people have hung mistletoe as a symbol of love and romance. But sadly, the plant doesn’t harbor the same feelings. Why?  Because mistletoe contains a Christmas cocktail of toxins that when ingested can harm humans and pets. I advise keeping it out of reach if you’re planning on hanging it this season.

WHAT MISTLETOE IS

Yes, despite its romantic associations, mistletoe is no loving plant. In fact, it is parasitic. That means it specializes in attaching itself to a tree or shrub and penetrating it to steal water and other nutrients.

And even though its leathery green balls add ‘life’ to bare branches, once mistletoe lays hold of a plant, it starts to destroy it. This often requires the removal of diseased limbs and in some cases entire trees in which there are large-scale infestations.

Attractive but parasitic bright green clusters of European mistletoe

As if that weren’t bad enough, the plant also spreads by seeds. Those pretty white berries? Birds love them. As they’re carried away, the berries’ sticky pulp drops from the sky, sowing mistletoe on other species.

All told, it can take up to two years for a mistletoe to fully develop. Once it takes root, it sends out aerial shoots that function as anchors. Over time, it grows through a plant’s bark and into its tissue, weakening and distorting it. Sometimes it even kills it.

WHAT HAPPENS IF I EAT MISTLETOE?

Worldwide, there are over a thousand mistletoe species. In North America, American mistletoe, Phoradendron serotinium, is the most common. Also known as Oak mistletoe due to its preference for oak trees, it is commercially harvested and sold around the world. All parts of the plant secrete a toxin called phoratoxin that can cause stomach upset, nausea and vomiting. That includes berries, leaves and stems.

Its cousin, Viscum album, known as European or Common mistletoe, is native to Europe, Southwestern Asia and Nepal. It contains a mix of chemicals that include poisonous amounts of the alkaloid tyramine. Tyramine can cause stomach upset, nausea and vomiting, blurred vision, blood pressure changes and in rare cases even death.

The oval leaves and white berries of Viscum album

The paddle-shaped leaves of Phoradendron

The good news is that, until recently, American mistletoe was widely considered to be as poisonous as the European species. Nowadays, though, the general consensus is that downing a few berries will probably lead to no more than a stomachache. In fact, according to the National Capital Poison Center’s recent studies describing American mistletoe exposures (mainly by young children at Christmas), you’d have to eat a whole lot of berries to experience these reactions.

As it happens, the vast majority of patients who ate parts of the plant had no negative effects. Moreover, there were no fatalities, even among those who had swallowed mistletoe on purpose. Still, it’s generally advised to keep it out of reach of children.

POISONING IN DOGS AND CATS

When it comes to pets, small amounts of mistletoe most likely will cause no more than mild gastrointestinal distress. However, if your cat or dog accidentally consumes large amounts of the plant, it could lead to abnormal heart rate, collapse or even seizures. If you suspect your pet has eaten mistletoe, contact your veterinarian or Pet Poison Helpline for treatment recommendations.

Mistletoe is most harmful to small children and pets/Photo credit: Michael Pettigrew

MISTLETOE AS MEDICINE

On a good note, perhaps due to its toxicity, Viscum album has been used by herbalists as medicine for centuries. This includes using it to improve circulatory and respiratory problems and to treat a variety of conditions including seizures, hypertension, headaches and arthritis. More recently, mistletoe extract has shown promise in stimulating the immune system in some limited laboratory studies. Today in Europe it is also being used as a cancer treatment.

(Although the United States FDA has not approved mistletoe as a treatment for cancer or any other medical condition, it is nonetheless being studied in clinical trials.)

Mistletoe is currently being harvested in Europe for its cancer-fighting properties

THE TAKE-AWAY

Used safely, mistletoe may do a lot more for humankind than just providing a romantic canopy. As we learn more and more about what plants can do, mistletoe’s powerful medicinal qualities are something to celebrate in addition to its decorative properties. Something to think about next time someone reaches in for a kiss under its branches.