St. John's Wort Poisoning in Cats

St. John's Wort Poisoning in Cats - Symptoms, Causes, Diagnosis, Treatment, Recovery, Management, Cost

What is St. John's Wort Poisoning?

St. John's wort is a species of flowering shrub that originated in Europe and Asia, but which has since spread across the globe as an invasive weed. The plant is viewed by most horticulturalists as a pest, due to both the difficulty of removing it from an area it has taken root in, as well as the toxicity of its tissues, which are a hazard to humans and animals alike.

Symptoms of St. John's Wort Poisoning in Cats

St. John's wort poisoning is potentially very dangerous for the animal in question. Should owners observe these symptoms, they should seek medical advice immediately.


  • Avoidance of bright lights 
  • Blistering
  • Boils 
  • Open sores 

Loss of Coordination

  • Unsteady gait 
  • Weakness
  • Difficulty manipulating obstacles and objects

Oral Irritation

  • Redness and swelling around the mouth
  • Drooling

Behavioral Change

  • Differences in personality and habits 
  • Agitation 
  • Pacing
  • Depression

Causes of St. John's Wort Poisoning in Cats

The chemical 'hypericin' is present in large amounts in the St. John's wort plant. Hypericin is a substance produced with the primary goal of neutralizing herbivores that may view the plant as potential food. The mechanism by which the substance works is twofold. Firstly, it is a natural inhibitor of a variety of hormones, which causes the bizarre behavior and loss of balance noted above. Secondly, once absorbed into the body (either via digestion or skin contact) it has the ability to bond with cells. If exposed to visible light, the hypericin undergoes a chemical reaction that changes the charge of its electrons, damaging or destroying the host cell in the process and causing burn-like symptoms. Interestingly, the chemical produces its highest concentrations in cells that are cancerous, making it an effective diagnostic tool in the field of oncology.

Diagnosis of St. John's Wort Poisoning in Cats

When the cat arrives at the clinic, the first thing the vet will do is perform a physical examination in order to confirm the nature of its symptoms and to check the animal's reactions, heart rate, breathing and other vital signs. Whilst this is going on, they will also try to get additional information on the case from the owner. The topics will usually include the circumstances surrounding the poisoning (i.e. what plants the owner believes to be at fault) as well as the cat's medical history and any prior incidents. The vet will oftentimes elect to perform a full blood panel test in order to both identify the exact substances at work and simultaneously rule out other causes.

Treatment of St. John's Wort Poisoning in Cats

The first order of business will be to prevent the cat from absorbing more hypericin and thereby exacerbating their symptoms. To this end, the vet may choose to administer either a dosage of hydrogen peroxide to the cat in order to induce vomiting or a dose of activated charcoal to absorb any chemicals still in the stomach. It may also be prudent to intravenously introduce some fluids into the cat's body in order to induce urination, which will help rid the cat's body of the toxins.

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Recovery of St. John's Wort Poisoning in Cats

After treatment has been completed, most animals will make a quick recovery within a few days. That said, those cats that have badly burned by exposure to sunlight will require some follow-up visits in order to ensure their wounds properly heal. Once home from the vet, the cat should be confined to a shaded room and given time to let the effects of the toxin wear off. The vet may also provide owners with a soothing or steroidal cream to apply to burned areas of the cat to assist their recovery.

St. John's Wort Poisoning Questions and Advice from Veterinary Professionals


long hair




14 Years


0 found this helpful


0 found this helpful

My pet has the following symptoms:
Poor Appetite
I'm not sure but my cat got very lethargic and didn't want to be touched, and she just kept getting worse. She wasn't eating very well. She wouldn't let us give her her medication. She would scream and growl which was not like her, when I gave her meds.

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