We don’t know why some cats don’t react to catnip! That’s the complete and unhelpful answer. The experts think that a cat is predisposed to reacting to catnip because of their inherited genes. But we don’t know what genes are the triggers.
The experts call it “the genetics of catnip sensitivity or susceptibility”. We don’t know for sure the percentage of cats who are susceptible. You’ll read various percentages from an estimated “up to one third” (book: Why does my cat do that?), “an estimated 50 percent (Humane Soc.), “about 70-80% (Scientific American) and 50-60% (catworld.com).
They believe that the “catnip sensitivity gene” is autosomal – not sex linked – dominant.
I have read that unsterilized males are more susceptible than sterilized males or females.
Hodder Education has an article on it. They use it as an example of dominant and recessive genes. They say that “the catnip sensitivity allele is dominant.
The reason why catnip does not affect kittens until they are about 3 months old is because the vomeronasal organ is not fully formed until that age. It is this hypersensitive olfactory organ which picks up the chemical “nepetalactone” in catnip through “nasal mucosa” and which sends a signal to the brain.
Older cats respond less than younger cats. Perhaps male cats respond more than females. The affect lasts for 5-15 minutes. Cats become tolerant to the drug after use which lasts for a few hours.
Catnip is a mint and it is an invasive species. If you grow it in the garden, you should place it in a large pot to confine the roots and place the pot in the flowerbed.
Cats sometimes eat catnip which is okay. There appears to be no negative health effects from either eating it or inhaling nepetalactone unless a lot is ingested and the cat vomits! The catnip plant is in the genus Nepeta.
Nepetalactone is an insect repellent. Nepetalactone is produced by many aphids as a sex hormone. The big cats are also affected by catnip. The affect can last for an hour.
The evolutionary reason as to why cats are attracted to catnip is as an insect repellent. The cats rub against the plants for this purpose. Nepetalactone repels Aedes albopictus, a species of mosquito, for instance.
It is proposed that as the classic mode of cat hunting is stalking followed by a dash, the cat is fairly static for a time which allows mosquitos and other insects to bite the cat. An effective repellent is useful under these circumstances which is why they rub against catnip if available.
SOME MORE ON CATNIP: