One of the stranger aspects of the modern human-pet relationship is that many cat owners recreationally dose their pets with a psychoactive drug. I'm talking, of course, about catnip.

Catnip is a bizarre phenomenon for a few reasons. It's the only recreational drug we routinely give to animals, and though it basically makes them freak out — rolling on the ground, drooling, and mashing their face into wherever the catnip was sprinkled — it has essentially no effect on us.

If you've ever wondered how it works, this article's for you.

Catnip is a plant

Specifically, that plant is Nepeta cataria, a shrub in the mint family. It's native to Europe and Asia but now grows wildly across the Americas as well, along roads and highways.

The plant produces a chemical called nepetalactone in microscopic bulbs that coat its leaves, stems, and seedpods. When these fragile bulbs rupture, they release the nepetalactone into the air.

How catnip affects cats

Cats get high off catnip by inhaling the nepetalactone — whether from a live plant, dried plant material, or an oil extract. The chemical binds to receptors inside a cat's nose, which stimulate sensory neurons leading into the brain. This appears to alter activity in several areas of the brain, including the olfactory bulb, the amygdala, and the hypothalamus. This last area, among other things, is involved in regulating the animal's emotions.

Scientists previously hypothesized that the chemical also triggered a reaction in something called the vomeronasal organ — an extra olfactory organ found deep in the nose in many mammals (but not humans) that's involved in detecting pheromones — but experiments have ruled that out. However, it is hypothesized that nepetalactone might mimic the shape of pheromones when binding to the nasal receptors.

Regardless of the underlying reason, nepetalactone triggers an intense, intoxicated reaction in most cats.

"If you put catnip on a scratching board, a cat will come along and sniff it, and then they'll start rubbing their face, then drooling, then rolling in it," says Jeff Grognet, a veterinarian who's previously written articles about the effects of catnip.

"They seem to have a sense of euphoria when they're doing all this, and then afterward, calmness. Once they're finished reacting, and they just sit there, it's like they're basically just a little bit buzzed." For about 30 minutes afterward, they sit there in a stupor, seemingly immune to being further affected by more catnip.

Nepetalactone isn't the only chemical that triggers this sort of response in cats. Others include actinidine and iridomyrmecin, which are both naturally found in various plants.

One interesting thing about this reaction, Grognet says, is that although it looks something like the frenzied, uncontrollable high a human might experience upon taking a hard drug, it's a bit different. "Catnip produces a very definite, repeatable response. A cat will pretty much do the exact same thing every time it smells it," he says. The cat isn't rubbing their face and rolling in the catnip to get more of it (as I'd assumed), but simply because getting high by inhaling the catnip compels them to do so.

Another difference between catnip and the drugs humans use is that not all cats are susceptible to it. It's estimated that around 70 percent to 80 percent are affected, and that the trait is passed on genetically. "They either react or they don't," Grognet says. "There's no in between." Lots of wild cats, like lions and tigers, are also susceptible.

For the cats that are susceptible, there don't appear to be any negative health effects, and they don't develop a tolerance over time.

Humans have used catnip too

Catnip doesn't have the same sort of impact on us, because our olfactory systems and brains are differently structured. But it may have some subtler effects, and people have been using it for a long time.

As far back as the 1600s, Europeans used the plant as a mild sedative, brewing tea with its leaves, making juice from them, and even smoking or chewing them. At various times, the plant was believed to cure colic in infants and excessive flatulence, hives, and toothaches in adult.

In the 1960s, catnip was occasionally used as a substitute for marijuana, with some users claiming it caused hallucinations and euphoria when smoked by humans. Eventually, though, scientists determined this was not the case.

It does, however, have one positive effect. Back in the 1960s, scientists discovered that catnip's active chemical acts as a mosquito repellant — one that's actually more powerful than DEET, though it wears off more quickly. In fact, if you want a less harsh alternative to DEET, catnip-based mosquito repellants are still available.