Yarrow, scientifically known as Achillea millefolium, is a perennial herb belonging to the Asteraceae family, which also includes daisies and sunflowers. It is characterized by its feathery, finely divided leaves (which give it the species name 'millefolium' meaning 'thousand leaves') and flat-topped clusters of small, tightly-packed flowers that can be white, yellow, pink, or red. Native to temperate regions of the Northern Hemisphere, yarrow is a hardy plant commonly found in meadows, grasslands, and along roadsides. It is also a popular ornamental plant in gardens due to its drought tolerance and attractive, long-lasting blooms.
From a phytochemical perspective, yarrow contains several bioactive compounds that contribute to its toxicity. The primary toxic agents are volatile oils, with the monoterpene β-pinene being a significant component. Additionally, yarrow contains achilleine, a glycoalkaloid, and lactones including sesquiterpene lactones. These compounds are part of the plant's natural defense mechanism against herbivores and pests. While these substances have been studied for potential medicinal benefits in humans, such as anti-inflammatory and antiseptic properties, they are metabolized differently by cats and dogs, leading to potential adverse effects.
The toxic principles in yarrow primarily affect the gastrointestinal system and the central nervous system of pets. The essential oils and sesquiterpene lactones are irritants that can cause inflammation of the mucous membranes upon ingestion. This leads to the most common clinical signs: vomiting, diarrhea, and drooling. In more significant quantities, the compounds can have a more systemic effect. Certain terpenes are known to be neurotoxic and can cause depression, ataxia (loss of coordination), and even, in rare cases of extreme ingestion, seizures. The plant's alkaloids can also contribute to these adverse neurological reactions.
If a cat or dog ingests yarrow, the severity of symptoms will depend on the amount consumed relative to the animal's size. The most frequently observed signs are gastrointestinal upset, including vomiting, diarrhea, and hypersalivation. A pet may also exhibit signs of anorexia or abdominal pain. Neurological signs, though less common, can include lethargy, depression, incoordination, and an unsteady gait. It is important to note that skin contact with the plant's sap can also cause dermatitis in some sensitive animals, resulting in redness, itching, or rash.
Given the presence of these toxic compounds, yarrow is considered to be mildly to moderately toxic to both cats and dogs. It is advisable for pet owners to prevent access to this plant. This can be achieved by not planting yarrow in gardens accessible to pets or by ensuring indoor dried floral arrangements containing yarrow are kept well out of reach. If ingestion is suspected, contacting a veterinarian or an animal poison control center immediately is crucial. Providing details about the plant and the estimated amount ingested will assist in determining the best course of action, which may include monitoring, inducing vomiting, or providing supportive care.
