While yarrow is often used by humans for its many medicinal benefits, the toxins within the plant do provide a risk of potential poisoning if a cat were to eat copious amounts of it. This is unlikely, as yarrow plants contain hydrosoluble tannins that are very bitter to the taste, preventing most cats from eating more than one bite. The achilleine glycoalkaloids, sesquiterpene lactones, and monoterpenes found in the plant can cause a general upset to the gastrointestinal system. There is also a risk of increased complications in cats who have many allergies, are pregnant or nursing, or who acquire wounds or incisions after yarrow consumption. Sesquiterpene lactones may also cause adverse skin reactions on the cat.
The yarrow is a very common perennial herb that can be found throughout North America. It is a slender plant, with green, feathered leaves tapering up the stem. Blossom clusters are found at the very top of the plant, and come in various colors. White or pale yellow are the most common colors of yarrow found in the wild. Hybrid yarrow may be used in gardens and can be bright yellow or red in color. It blooms all summer long, right into the fall. Yarrow goes by multiple names including milfoil, soldier's woundwort, bloodwort or field hops, but its scientific name is actually Achillea millefolium. It is a part of the Asteraceae family of plants.