Is Equisetum japonicum toxic to dogs?

Mildly. The ASPCA lists equisetum japonicum as mildly toxic to dogs — a chewing dog typically gets mouth irritation, drooling, and vomiting rather than a medical emergency, but it is still best kept out of reach. Japanese horsetail is not individually listed by the ASPCA, but the genus Equisetum is ASPCA-listed as toxic to horses through thiaminase, which causes thiamine deficiency (weakness, tremors, staggers, death). Dogs and cats are not flagged, yet given the known toxic principle treat with caution and verify with a vet before assuming it is safe.

Japanese horsetail is not individually listed by the ASPCA, but the genus Equisetum is ASPCA-listed as toxic to horses through thiaminase, which causes thiamine deficiency (weakness, tremors, staggers, death). Dogs and cats are not flagged, yet given the known toxic principle treat with caution and verify with a vet before assuming it is safe. 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 dog has had access to equisetum japonicum.

Stay calm. Remove any plant from your dog'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: Equisetum japonicum is mildly toxic to cats as well. See the full equisetum japonicum pet-safety guide for both species.

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