Is Water Horsetail toxic to cats?

Mildly. The ASPCA lists water horsetail as mildly toxic to cats — a chewing cat typically gets mouth irritation, drooling, and vomiting rather than a medical emergency, but it is still best kept out of reach. Equisetum species are considered mildly toxic to cats, dogs, and horses. They contain thiaminase (an enzyme that destroys thiamine/vitamin B1) and alkaloids including equisetine. Large quantities consumed can cause neurological signs, particularly in horses and livestock. The ASPCA does not individually list E. fluviatile but the genus is generally treated as toxic by veterinary authorities. Keep pets away from horsetail patches.

Equisetum species are considered mildly toxic to cats, dogs, and horses. They contain thiaminase (an enzyme that destroys thiamine/vitamin B1) and alkaloids including equisetine. Large quantities consumed can cause neurological signs, particularly in horses and livestock. The ASPCA does not individually list E. fluviatile but the genus is generally treated as toxic by veterinary authorities. Keep pets away from horsetail patches. Signs usually appear soon after chewing rather than hours later — watch for drooling, pawing at the mouth, vomiting, loss of appetite, or unusual lethargy after your cat has had access to water horsetail.

Stay calm. Remove any plant from your cat's mouth and take the plant away. Note how much was eaten and when, and do not induce vomiting unless told to. Call your vet or the ASPCA Animal Poison Control Center on (888) 426-4435 and follow their advice; a leaf or photo helps the vet treat it correctly.

The ASPCA classification Growli uses applies to both cats and dogs: Water Horsetail is mildly toxic to dogs as well. See the full water horsetail pet-safety guide for both species.

For a similar look without the risk, see the best cats-safe plants list — every plant there is ASPCA non-toxic to cats and dogs.