Mayweed is made up of a plethora of toxins, including terpenoids, volatile oil, flavonoids, coumarins, chamazulene, and anthemic, tannic and fatty acids. These toxins make mayweed a threat to cats, although life-threatening cases of consumption are generally not heard of. Some of the toxins are known to produce allergic reactions if eaten or if touched by the skin of an animal. The combination of the many toxins in the mayweed also make it taste quite bad, which deters most cats from consuming harmful quantities of it.

Anthemis cotula of the Asteraceae plant family, or mayweed as it is often called, is an invasive annual plant that has spread all over the United States. Mayweed blossoms resemble daisies, having bright yellow centers surrounded by white petals, although their aroma is strong and generally regarded as bad. This has resulted in mayweed also being called “stinking chamomile” or “poison daisy”. Mayweed is native to the Mediterranean, but due to its hardiness and high germination rate it has aggressively spread throughout the country and is now classified as a noxious weed for its ability to take over crop lands. The seeds of the plant can lay dormant in soil for up to 25 years.

Depending on whether the contact with the plant is made internally or externally, various symptoms will develop. There is a potential risk of the cat's blood being affected if mayweed is consumed for a lengthened period of time. All signs to watch for include:

Because this plant is so invasive, it can be found growing in many places. The most common locations for mayweed to grow are roadsides, fields, waste lands, or amongst crops. This means that cats who are allowed outdoors, especially in rural areas, are at a heightened risk of coming into contact with the plant. The immediate oral irritation that often follows chewing the plant stops most cats from taking more than one bite. 

If you witnessed your cat eating a plant prior to symptoms arising, bring a trimming of the plant with you so poisoning can be confirmed. If you did not witness your cat eating anything unusual but symptoms have begun to develop, take it in to be professionally assessed by a veterinarian. You may be asked to provide the cat's full medical history to look for any pre-existing conditions that may have lead to the symptoms being exhibited. You may also be asked if you allow your cat outdoors, and what kind of area you live in.

The veterinarian will then perform a complete physical examination of the cat to check for any other abnormalities that may exist. While looking in the oral cavity, the vet may notice bits of plant material stuck between the cat's teeth. A sample of blood will be taken from the cat for routine testing to be done. These tests often include a complete blood count and a biochemical profile to measure all cell and mineral levels in the bloodstream. A sample of the cat's urine may also be collected so that all materials being poured out with the urine can be noted. 

Poisoning from a mayweed plant is not usually serious, however, treatment may still be needed to ease the cat's symptoms and promote a quick recovery.

Flushing the mouth with water will both soothe the irritation caused by the toxins and remove all remaining bits of plant before they are ingested. If other parts of the cat have come in contact with the plant, they also may need to be washed.

All contents of the stomach should be removed as fast as possible. If the cat is in a relatively stable condition, hydrogen peroxide may be administered to induce vomiting. A gastric lavage (stomach pumping) may be performed if the cat is in a more fragile state.

This may be given to absorb all remaining toxins in the digestive tract and trap them so that they may safely pass through the intestines undigested. 

If the cat has undergone an extensive period of vomiting or diarrhea, it may become dehydrated. Intravenous fluids can be administered to help bring volume levels back up in the cat. Hospitalization is required for this process. Medications such as Kapectolin or sucralfate may be given to protect the stomach lining from the irritation caused by the toxins. 

Most cats who have been poisoned from eating mayweed will go on to make a complete recovery. The cat should be monitored throughout the period of illness, but no related health problems should exist after the illness has passed. As this weed can grow almost anywhere, keeping your cat indoors may be the best defense against a potential plant poisoning.

If you locate Mayweed on your property or in the surrounding areas, it may be best to remove it before it spreads. Carefully research the recommended ways of eradicating it and do so naturally if possible. Inform your neighbors about the plant and its potential dangers.