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They also go wild for other plants, particularly silver vine, which is not closely related to catnip but elicits the same response from felines, including big cats like jaguars and tigers.

Botanically speaking, catnip and silver vine are distant cousins.

For the most part, cats with silver vine chemicals on their heads were left alone, while those without the iridoids were covered in mosquito bites.

But exactly how catnip—and a substitute, known as silver vine—produce this feline high has long been a mystery.

Playthings containing silver vine have been shown to attract cats more than catnip, and it is said to have a calming effect, Bahr said.