I have two cats at home, Rusty and Foo, who have very different characters. I gave them both some catnip the other day and they had two very different reactions.

Foo sniffed it suspiciously and walked away, seemingly unaffected, whereas Rusty began rolling around in the dried leaves of the herb, drooling and purring as if in raptures. It got me thinking about their differing reactions and what the catnip is actually doing to them. Here’s what I found out.

The scientific name for catnip is Nepeta cataria. It is classified as a herb in the mint family. Catnip produces an organic compound called nepetalactone, which enters a cat's system through the nasal passages. Nepetalactone gets released when the plant is crushed or chewed. A cat rubbing against fresh or dried pieces of the plant can also release the nepetalactone. Once your cat inhales nepetalactone, the molecules bind to olfactory cells in the nose, which sends a signal to the brain that makes the behavioural changes.

Some cats become hyperactive and run around, climbing trees and furniture. Some, like Rusty, become more relaxed and hypersalivate or drool. There is no way to predict how your cat will react but there is evidence to show that the tendency to react is genetic. About thirty per cent of domestic cats, like Foo, show no reaction at all. Adult cats tend to react more than the very young or very old cats. Lions and tigers have both been shown to react to catnip.

The effects of catnip are short lived, from around ten minutes up to half an hour. Cats can also develop an immunity to catnip if offered it too frequently. It is better to give it here and there as a treat rather than too often. Many toys have catnip added, which may explain why cats like the new toy but quickly seem to get bored with it.

Catnip has been used as a reward, or in potentially stressful events to help calm cats down. It has also been used in weight loss as a way to stimulate activity. If you are offering catnip for the first time to your pet, give a small amount and see how they react. If they like it, consider growing some in the garden or in a pot, but remember the fresh leaves are more potent than the dried ones.

Judging by Rusty’s reaction, he would probably be happy lying in a large patch of catnip watching the butterflies for most of the day but I’m not sure Foo would allow that, and she’s the boss.

• Lucy Richardson graduated from Edinburgh University in 2005. She started CedarTree Vets in August 2012 with her husband, Mark. They live at the practice with their two children, Ray and Stella, and their dog, two cats and two guinea pigs. She is also the FEI national head veterinarian for Bermuda