Watercress (Nasturtium officinale) is an aquatic plant native to Europe and Asia but now grows wild throughout the United States and southern Canada. Watercress is used as an herbal supplement and food flavoring for both humans and canines, although it does have compounds that can be moderately noxious in large quantities. If your pet eats watercress that is meant for consumption, any ill effects should be minor. Eating wild watercress comes with additional hazards for your and your pet and should be executed carefully, or avoided.

Watercress (Nasturtium officinale) is an aquatic plant that is used as an herbal supplement and flavor enhancer. It is mildly noxious and may cause gastrointestinal upset for your pet.

In most cases, the few symptoms you will see from your pet eating watercress will be related to the Glucosinolate–myrosinase complex inherent in these and other botanically similar plants, such as mustard and horseradish. The metabolite glucosinolate and the enzyme myrosinase are kept in separate compartments in the plant until the plant is crushed or cut. When the glucosinolate and myrosinase combine, the reaction causes the compounds to break down. This is what gives these plants their pungent, spicy flavor and can cause nausea, vomiting, and diarrhea if consumed in large quantities. Kidney and thyroid damage may occur with repeated or excessively large exposures or in animals with weakened systems.

Watercress in the Wild  – Your pet may encounter wild watercress (nasturtium officinale) in watery areas throughout the United States. It is important to note that water hemlock often grows in the same area as watercress and can be fatal even in small doses. Watercress also tends to soak up the compounds in the water that it grows in, including any toxins in the water. These may become concentrated in the plant, making the plant hazardous to eat. 

Watercress in the Grocery Aisle - Watercress is frequently used in leafy salads and in soups and sandwiches. It has a flavor profile similar to mustard greens or mild horseradish, is rich in several key vitamins and minerals, and is known for its anti-inflammatory properties. 

Watercress in Dog Food - Watercress is occasionally found in dog food as a source of vitamins and minerals and as a flavor enhancer. It is found in just over 1% of all dog foods.

Although watercress itself is not particularly toxic to your pet, it can cause nausea, vomiting, and diarrhea in large doses. Watercress that is growing wild can come with additional risks, however. Watercress is known to soak up toxins and bacteria in the water which then become concentrated within the plant which can cause anything from heavy metal poisoning to infections such as listeria in your pet. 

Watercress also grows in the same environment as the water hemlock. Water hemlock is a highly toxic plant and can cause fatalities with as little as one leaf. Symptoms of water hemlock poisoning can include:

If your pet shows symptoms consistent with water hemlock poisoning, rush the patient to the nearest veterinarian or emergency animal clinic as fatalities can occur within as little as 15 minutes.

As watercress plants are only mildly noxious, symptoms that are more critical than mild vomiting or diarrhea are usually due to a secondary disorder or to a misidentification of the plant. Questions regarding your canine’s health background, dietary habits, oral medications, access to plants or other potential toxins, and current symptoms are all likely to be covered. A thorough physical exam will be performed with particular attention being paid to the stomach and abdomen area to check for intestinal blockages. 

A complete blood count (CBC), urinalysis, and biochemistry profile will also generally be requested. This is completed in order to detect if there are any toxins or imbalances in the patient’s system. If a sample of the plant was brought in, the sample may be evaluated to see if there are any toxins that may have been absorbed by the plant itself. If symptoms of poisoning are occurring but the consumption of the toxin was not witnessed then any contents of the stomach will be tested for plant material or other toxins. If the vomiting is severe, your veterinarian may recommend that anti-emetic and gastroprotective medications be administered to reduce acute symptoms.

Early therapy for dogs showing gastrointestinal distress generally involves the withholding food until the vomiting and diarrhea have ceased for approximately half a day. This technique is designed to give the dog’s stomach muscles time to recover from the gastric spasms caused by the vomiting and may be what your veterinarian recommends. Water and crushed ice should often be offered during this treatment to combat dehydration, but only in small amounts. Only soft, bland foods should be provided for at least a day or two after the withholding period to avoid additional gastrointestinal distress. The ideal recovery diet should include one easily-digestible carbohydrate and one mild protein source. 

If excessive vomiting or diarrhea become a concern, or if symptoms unrelated to watercress toxicity develop, your veterinarian will recommend bringing your pet into their office for additional supportive treatments. IV fluid treatment will most likely be administered at the veterinarian’s office to prevent dehydration, and medications like Pepcid AC or Imodium may also be recommended for their gastroprotective properties. Do not give these medications to your pet without proper individual dosing amounts given to you by a veterinary professional.

Prognosis for canines who have watercress is usually quite good, and any reactions to the plant itself should dissipate within 24 hours. The prognosis may be altered if your pet has sampled a plant other than watercress or if the watercress that was eaten was contaminated. One of the biggest dangers with profuse vomiting and diarrhea is the risk of dehydration. Your companion should be vigilantly monitored for signs of dehydration such as sunken eyes, excessive panting, and loss of skin elasticity. A severely dehydrated animal may also experience exhaustion and unsteadiness when standing. Any of these symptoms may signal that the dog is in serious distress, and your veterinarian should be contacted for further instructions.