My colleague has had to start hiding her "sleepy tea" teabags from her pets when she found out they contain catnip.

"I have to fight my cats to get through a cup," she told me, revealing that her furry friends clamour around the mug, trying desperately to find the source of the scent.

Anyone who owns a cat will have likely seen their companion's reaction to the herb, which is actually a member of the mint family.

But why are most cats (70%) so enamoured by the plant?

Surely there's some scientific explanation as to why they can't get enough of the herb that doesn't even exist in the areas where they evolved?

If you've ever looked at a cat rolling in catnip, thought "I wish humans had an equivalent", and then decided that actually, the closest stuff we have probably isn't legal, science has your back.

Though cats can't get addicted to catnip, scientists wrote a paper in 2021 that explained that the "opioid system regulating euphoric and rewarding effects in humans is involved in the expression of the catnip and silver vine response in cats".

That's because compounds called iridoids -- specifically, an iridoid called nepetalactone -- are picked up by cats in their extra scent organ called the vomeronasal gland.

Iridoids, which scientists found can act as mosquito repellants, raise cats' beta-endorphin levels (also known as "happy hormones") and cause behavioural changes like rolling and purring.

Researchers think nepetalactone might also mimic feline pheromones. Catnip seems to affect older cats and kittens less than breeding-age cats.

Biologist Dr Masao Miyazaki, who co-authored the study that found nepetalactone works as a mosquito repellant, told Science: "Our findings suggest instead that rolling is rather a functional behaviour."

That's because it covers more of their body in the pest-repelling substance, which is useful as mosquitoes can get in the way of a good hunt, he explains.

When Dr Miyazaki and his team blocked some cats' opioid receptors before exposing them to catnip, they did not rub against the plant.

"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," the researcher shared.

If only my reaction to chocolate (which is honestly not dissimilar to cats with catnip) was as rational.