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Cat owners flood the internet with videos of their kitties euphorically rolling and flipping out over catnip-filled bags and toys. But exactly how catnip—and a substitute, known as silver vine—produce this feline high has long been a mystery. Now, a study suggests the key intoxicating chemicals in the plants activate cats’ opioid systems much like heroin and morphine do in people. Moreover, the study concludes that rubbing the plants protects the felines against mosquito bites.

"This study essentially has revealed a new potential mosquito repellent” by examining the “pharmaceutical knowledge” of cats, says Emory University biologist Jacobus de Roode, who did not participate in the study.

Catnip (Nepeta cataria) and silver vine (Actinidia polygama) both contain chemical compounds called iridoids that protect the plants against aphids and are known to be the key to the euphoria produced in cats. To determine the physiological effect of these compounds, Iwate University biologist Masao Miyazaki spent 5 years running different experiments using the plants and their chemicals. 

First, his team extracted chemicals present in both catnip and silver vine leaves and identified the most potent component that produces the feline high: a minty silver vine chemical called nepetalactol that had not been shown to affect cats until this study. (The substance is similar to nepetalactone, the key iridoid in catnip). Then, they put 10 leaves’ worth of nepetalactol into paper pouches and presented them, together with pouches containing only a saline substance, to 25 domestic cats to gauge their response. Most of the animals showed interest only in the pouches with nepetalactol.

To make sure this was the object of the felines' attraction, they repeated the experiment with 30 feral cats—and one leopard, two lynxes, and two jaguars living in Japan’s Tennoji and Oji zoos. Big or small, the felines surrendered to the substance, rubbing their heads and bodies in the patches for an average of 10 minutes (see video, above). In contrast, dogs and mice that were tested showed no interest in the compound.

Next, the researchers measured beta-endorphins—one of the hormones that naturally relieves pain and induces pleasure by activating the body’s opioid system—in the bloodstreams of five cats 5 minutes before and after exposure. The researchers found that levels of this “happiness hormone” became significantly elevated after exposure to nepetalactol compared with controls. Five cats that had their opioid systems blocked did not rub on the nepetalactol-infused pouches.

But the researchers wanted to know whether there was a reason for the cats to go wild, beyond pure pleasure. That is when one of the scientists heard about the insect-repelling properties of nepetalactone, which about 2 decades ago was shown to be as good as the famed mosquito-stopper DEET. The researchers hypothesized that when felines in the wild rub on catnip or silver vine, they’re essentially applying an insect repellant.

They first showed cats can transfer the chemical to their skin, and then conducted a live mosquito challenge—similar to when people’s arms are used to evaluate insect repellants. They put the nepetalactol-treated heads of sedated cats into chambers full of mosquitoes and counted how many landed on them—it was about half the number that landed on feline heads treated with a neutral substance, they report today in Science Advances.

Most scientists and pet owners assumed the only reason that cats roll around in catnip was for the euphoric experience, Miyazaki says. "Our findings suggest instead that rolling is rather a functional behavior.”

The researchers speculate that cat ancestors might have rubbed their bodies against the plants by chance, enjoyed the feeling, and kept doing it. It is not clear, though, whether it was the euphoric response—or the insect-repelling properties of the plant—that kept them rolling. "Anyone who has ever sat in the field to observe animals ambushing prey knows just how difficult it is for them to keep still when there are many biting mosquitoes around," Miyazaki says. "It does not seem unreasonable, therefore, to argue that there is a strong selection pressure” to keep away annoying bugs.

The team, which has already patented an insect repellent based on nepetalactol, plans next to identify the cat genes involved in the catnip response and examine the substance's action against other insect pests. De Roode, who is impressed by how thorough the experiments were, says the work provides a "really interesting" example of how insects can shape animal behavior. "It is amazing how much we can learn from animals."