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Pennyroyal Oil from Poisonous Plant for Dogs

Pennyroyal oil is derived from plants within the mint family known as Labiatae. It is frequently used in flea powders and sprays and in fragrances. It can be toxic to dogs, particularly when ingested. There has been one reported case of a dog suffering pennyroyal oil poisoning from dermal (skin) exposure as well.

Symptoms and Types

Symptoms expected with pennyroyal oil poisoning include:

  • Listlessness
  • Vomiting
  • Diarrhea
  • Coughing up blood
  • Difficulty breathing
  • Bloody nose
  • Lethargy
  • Coma
  • Seizures
  • Death


The active poison in pennyroyal oil is a chemical known as pulegone, which is toxic to the liver and can cause severe liver damage.


Physical examination findings consistent with pennyroyal oil poisoning together with a history of exposure to plants, fragrances, or flea products containing pennyroyal oil may prompt suspicion of toxicity.

Blood tests reveal abnormalities consistent with liver damage, including elevated liver enzymes (alanine aminotransferase, alkaline phosphatase, aspartine aminotransferase, gamma-glyamyl transferase) and evidence of bleeding (anemia and prolonged clotting times.)

Evidence of hemorrhage (bleeding) may be seen in internal organs, such as the lungs, liver and kidneys.

A definitive diagnosis may be obtained by finding pulegone on gas chromatography (a specialized laboratory test that analyzes for specific chemicals.)


Vomiting can be induced if the dog is not comatose, having respiratory difficulties or having seizures. Gastric lavage (washing out the stomach) may be performed and activated charcoal is frequently administered to bind the toxin.

Bathing with a mild shampoo to remove any pennyroyal oil on the skin and hair coat is recommended.

Fluid therapy may be necessary along with supportive nursing care. N-acetylcysteine may be recommended as well as liver protectants such as S-Adenosylmethionine, Ursodeoxycholic acid, or vitamin E. Gastrointestinal protectants such as cimetidine and/or carafate and antiemetic medidogions to control vomiting may also be used. Antibiotics are frequently administered also.


Use precaution when applying flea products containing pennyroyal oil on dogs. Be sure to follow label directions carefully to avoid overdosing.

Also, keep dogs away from garden plants and other products which contain pennyroyal oil.

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