St. John's Wort Poisoning in Dogs

St. John’s wort (Hypericum perforatum), also known as Klamath weed, is a member of the Clusiaceae family and is toxic for dogs, causing photosensitization (sun sensitivity) and contact dermatitis. Hypericin contained in the plant leads to the symptoms that your dog may experience from ingesting St. John’s wort. A perennial, St. John’s wort can grow up to three feet tall with blooms that are one inch in diameter (yellow star-shaped flowers). While St. John’s wort is helpful for certain health issues in people, any amount can be toxic to your dog.

Also known as klamath weed, St. John’s wort contains hypericin, which is toxic in dogs and its ingestion can lead to photosensitization and various other health issues.

While there are differences of opinion present in the reports of the symptoms of poisoning with St. John’s wort, the most common ones reported include:

• Fever
• Photo sensitization
• Skin ulcers, blisters, lesions
• Vomiting
• Loss of appetite
• Diarrhea
• Blindness
• Increased heart rate
• Convulsions

With ingestion over the long term, symptoms may include:

• Liver damage
• Skin cancer

While St. John’s wort ingestion can be fatal, that outcome is very rare. If you notice that your dog has ingested St. John’s wort, or suspect that he has, you will want to get him out of the sun immediately.

Types 

While the scientific name of St. John’s Wort is hypericum perforatum, it goes by several other names, to include:

• Klamath weed
• Tipton weed
• St. Andrew’s cross
• Rosin rose
• Goat weed

Poisoning from St. John’s wort is due to the hypericin the plant contains. While hypericin can be found throughout the plant, it is most potent in the areas that have black dots, like the flower petals. Hypericin glows when exposed to sunlight, leading to inflammation and necrosis, thus the skin condition resulting from St. John’s wort poisoning, which can happen from consuming the plant. The skin condition can be made worse through sun exposure and can lead to other complications as well.

Should you have witnessed your dog ingesting St. John’s wort, or a plant that you believe he is having a reaction to, taking a picture of the plant or bringing a sample for testing into the veterinarian’s office will be helpful for diagnosis. If you saw your dog consuming the plant, let the veterinarian know about how much your dog ate and around what time he ate it. Your veterinarian will ask you what symptoms you have noticed and for how long you have noticed them; if this is not your usual veterinarian, you will also be asked what medications, if any, your dog is taking. 

Your dog will undergo a physical examination, where your veterinarian will check your dog’s coat, weight, blood pressure, temperature, breath sounds and reflexes. His skin, eyes, ears, nose and mouth will be looked at to determine if there are any lesions. Depending on the physical examination, your veterinarian may consider the following tests:

• Urinalysis and stool sample, which can confirm if an infection or other cause of symptoms is present in your dog
• Blood tests, to include a complete blood count, chemical profile, liver enzyme panel, blood urea nitrogen (BUN), packed cell volume (PCV) and arterial blood gas (ABG)
• Blood glucose test, hematocrit, creatinine (CREAT) level profile
• Endoscopy (to look for ulcerations and plant residue within your dog’s throat and airway)
• X-rays of your dog’s abdomen, to see if there is inflammation or ulceration within your dog’s gastrointestinal tract and esophagus
• MRI or CT scan if more detail is needed

Should your dog experience poisoning from St. John’s wort, the first aspect of treatment will be to get the toxins out of his system. If your dog has not been vomiting since ingesting the toxin, your veterinarian may induce vomiting. Activated charcoal can be utilized to absorb any of the toxins that your dog has not eliminated. Your veterinarian may then choose to conduct a gastric lavage that will rinse the toxins in your dog’s system that have not been digested, as well as flush his kidneys and ensure he remains hydrated.

Depending on the level of pain your dog is experiencing, your veterinarian may recommend pain medication and prescribe an ointment for any dermatitis or ulcers. Should your dog be experiencing significant inflammation, corticosteroids may be given. With the exception of significant issues resulting from the poisoning (like liver toxicity), you should be able to take your dog home right away.

A full recovery from St. John’s wort poisoning is very likely for your dog. They key is to make sure he is treated for the poisoning before he experiences significant sun damage to his skin. You will want to ensure that there is no St. John’s wort in your dog’s diet. It is recommended that you limit your dog’s exposure to sunlight and keep his skin covered when exposed, either with clothing or sunscreen.