Mistletoe is mildly to moderately poisonous to dogs, cats, horses, and other animals. The good news: severe toxicity is uncommon and typically only occurs when a pet eats a large amount. A review of American mistletoe exposures found that 99.2% of cases resulted in no lasting harm, and there were zero fatalities.
That said, mistletoe does contain real toxins that can make your pet sick, and the risk varies depending on which type of mistletoe is involved and how much was eaten.
What Makes Mistletoe Toxic
Mistletoe contains two main groups of harmful compounds. The first group, called lectins, shuts down protein production inside cells and triggers cell death. These proteins are structurally similar to ricin, the well-known toxin from castor beans. The second group, called viscotoxins (in European mistletoe) or phoratoxins (in American mistletoe), damages cell membranes directly, causing tissue destruction.
Both groups of toxins affect the cardiovascular system. They can slow the heart rate, drop blood pressure, and increase activity in the gut and uterus. Mistletoe also contains compounds like choline and acetylcholine that contribute to a temporary drop in blood pressure.
American vs. European Mistletoe
There are two broad categories of mistletoe, and they are not equally dangerous. American mistletoe (the kind commonly sold as a holiday decoration in the United States) has relatively lower toxicity. European mistletoe, which is more often used in herbal and folk medicine products, contains higher concentrations of lectins and is considered the more toxic of the two. If your pet got into a sprig of holiday mistletoe in North America, you’re most likely dealing with the less toxic American variety.
Symptoms in Dogs and Cats
The most common signs of mistletoe ingestion in dogs and cats are gastrointestinal: vomiting and diarrhea. These often appear within a few hours. In more significant exposures, you may also see difficulty breathing, weakness (from lowered blood pressure or a slowed heart rate), and unusual behavior. The ASPCA’s Animal Poison Control Center identifies these cardiac effects as the primary serious concern, but again, reaching that level of toxicity requires eating a substantial quantity.
Most pets that nibble a few leaves or berries will experience mild stomach upset at worst. The berries are often considered the most tempting part for curious dogs, and while they do contain the plant’s toxins, a few berries are unlikely to cause anything beyond temporary digestive discomfort in a medium or large dog. Small dogs and cats face higher risk simply because of their lower body weight.
Risks for Horses and Livestock
Horses can encounter mistletoe if it’s hung near a stall door or tossed into a pasture after the holidays. In horses, the primary symptom is colic rather than vomiting (since horses can’t vomit). Difficulty breathing, weakness, and behavioral changes are also possible. Interestingly, cattle and some wild animals regularly browse on mistletoe growing in trees without obvious ill effects when eating it in small amounts. Research has noted that mistletoe can function as forage for livestock, but concentrated or injected doses are a different story entirely: in lab settings, injecting mistletoe extracts into mice proved lethal, with death occurring either immediately or within two to four days depending on which toxin was involved.
The key distinction is the dose. Animals grazing casually on mistletoe in a field get small, spread-out exposures. A horse eating an entire holiday bouquet is a different situation.
What to Do if Your Pet Eats Mistletoe
Despite mistletoe’s reputation as a deadly plant, the actual data is reassuring. A large review of American mistletoe cases found no fatalities and virtually no serious outcomes. Both the general public and medical professionals tend to react more aggressively to mistletoe ingestion than the evidence warrants.
Still, if your pet eats mistletoe, the practical steps are straightforward. Note roughly how much was consumed and which part of the plant (berries, leaves, stems). Contact your veterinarian or the Pet Poison Helpline for guidance specific to your pet’s size and the amount eaten. For a large dog that ate a single berry, you’ll likely be told to watch for vomiting and diarrhea at home. For a small cat that chewed through a full sprig, your vet may want to see the animal for monitoring.
Most pets recover fully with nothing more than supportive care. The vomiting and diarrhea that mark mild cases are self-limiting, meaning they resolve on their own once the plant material passes through. Keeping your pet hydrated during this period is the main concern. Serious cardiovascular symptoms, while possible in theory, are rare enough that most veterinarians will never see a true case of severe mistletoe poisoning in their entire career.
Keeping Pets Safe During the Holidays
The simplest prevention is hanging mistletoe well out of reach or using artificial mistletoe instead. Dogs are more likely than cats to eat plant material off the floor, so fallen berries are worth picking up promptly. If you have horses, avoid decorating barn areas with real mistletoe and never discard holiday greenery where livestock can reach it. Mistletoe growing wild in trees is generally a low concern for pastured animals, since they self-regulate their intake and the plant is diluted among other forage.