Are Hydrangeas Toxic to Cats

Are hydrangeas toxic to cats?

Hydrangeas are toxic to cats. The toxic principle is amygdalin, a cyanogenic glycoside (CGs) which are natural toxins to protect the plant from herbivores. When the cell structure of a plant is damaged, cyanogenic glycosides will be brought together with the corresponding hydrolytic β-glucosidase enzyme. The glycoside degenerates to a sugar and cyanohydrin which decomposes into hydrogen cyanide and aldehyde. Cyanide is a fast-acting toxin that enters the bloodstream where it is changed into thiocyanate, which is less harmful. In large doses, the cat’s ability to change cyanide into thiocyanate is overwhelmed and cells are prevented from using oxygen and eventually die.

The risk to cats is minimal as a large amount of plant matter would need to be consumed to induce cyanide toxicosis. However, consumption can lead to gastrointestinal disturbances.

What is hydrangea?

  • Botanical name: Hydrangea spp.
  • Common names: Hydrangea, Penny mac, Hortensia
  • Toxicity: Toxic to cats
  • Toxic parts: All parts, flowers and young leaves are the most toxic
  • Severity: Mild to moderate
  • Toxic principle: Cyanogenic glycoside

Hydrangeas are a species of 70–75 species of flowering shrubs native to Asia and the Americas. Their lush, ball-shaped flower clusters make them popular as a cut flower, garden or pot plant. Blue and pink hydrangeas change their colour depending on soil pH.

Clinical signs

Cyanide toxicity is rare in cats, the most common manifestation of hydrangea ingestion relate to gastrointestinal disturbances. Clinical signs typically take 30 minutes to develop and may include:

  • Loss of appetite
  • Vomiting
  • Diarrhea

First aid

If you suspect your cat has consumed hydrangea, contact your local veterinarian or pet poison helpline for advice. They may recommend a wait and see approach if only a small amount of plant has been consumed and the cat is not displaying clinical signs of toxicity. When taking a cat to the veterinarian, bring along a sample of the plant for identification.

Treatment will depend on how long ago ingestion occurred as well as presenting symptoms but may include inducing vomiting if the exposure was recent and administration of activated charcoal to bind to any remaining plant matter in the stomach.

Severely affected cats will require hospitalisation and intravenous fluids to flush toxins from the body and correct dehydration and electrolyte derangements.

The veterinarian may recommend a bland diet such as chicken and rice for the next few days while the gastrointestinal tract recovers.


The only way to prevent hydrangea toxicosis is to not grow them in areas the cat can access. There are many cat-safe alternatives to grow in the garden or pots.


  • Julia Wilson, 'Cat World' Founder

    Julia Wilson is the founder of Cat-World, and has researched and written over 1,000 articles about cats. She is a cat expert with over 20 years of experience writing about a wide range of cat topics, with a special interest in cat health, welfare and preventative care. Julia lives in Sydney with her family, four cats and two dogs. Full author bio