That cats go crazy over catnip is no secret. All three of our boys, find their "kitten within" when presented with a new catnip toy or a recycled sock filled with catnip. Even our Angel Cat, Bubba, was kittenish over catnip in his advanced years. It's sort of like the old "chicken and egg" conundrum. Did catnip get its name because cats are so nuts over it, or did they fall for the oldest marketing ploy in the world? Strangely enough, not all cats are wild for catnip, and we've noticed our cats have a definite "tolerance level" for it. Usually after 15 or 20 minutes they get bored with catnip, or simply drift off to sleep.
Actually, catnip (its biological name is 'nepeta cataria'), has been used as a tranquilizer or sedative for humans for centuries. Catnip also has been prescribed for respiratory conditions, as an aid to digestion, and for such disparate conditions as menstrual cramps and toothache, by ancient and modern herbalists, according to this excellent article by HolisticOnline.
You will find a wealth of catnip-stuffed toys, as well as bags or canisters of dried catnip on the market. Since the scent is the powerful aphrodisiac that attracts cats, try to have a "fresh" supply at all times, and experiment with various brands, until you find one that is most attractive to your cats.
Catnip is also known as "Cat Mint," and is about as easy to grow as mint. Because catnip tends to become invasive, when planted in a garden, I grow it in wood planters in my Cat Garden. It can be easily grown from seed, and prefers a sandy soil and full sun. If you have a cat who is allowed outdoor it's a good idea to shelter the small plants with some staked netting or a piece of window screening tented over the container. We learned this lesson after our angel kitty Bubba rolled in a freshly-planted bed of catnip, crushing and breaking off some of the biggest stems. We salvaged what we could, and cut off the broken stems to dry for a catnip sock.
A good craft project that you and your cats will enjoy equally, is to fill some odd-matched socks with a bit of fiberfill, generously packed with dried catnip. Either knot the end (if it is a long sock), tie it with strong twine, or cut the open end short and sew it closed by using very strong thread and a whip stitch. Or, if you're making kitty gifts for a special occasion, you can purchase colorful baby socks (the color is for human pleasure, not necessarily the cats'). I use a "double-whammy" method of closure with the baby socks. I tie the top tightly about two inches down, fold the top down over the tie, and then stitch both at the top of the fold and the bottom. It makes an attractive gift, and the extra time investment ensures that the cats won't be able to tear the sock open. These socks may lose their "potency," after a few weeks, but a short time in your dryer on low heat will fluff them up again and regenerate the "sniff" factor. If all else fails, you can open them up and add fresh 'nip for another cycle of fun. If you're like me, though, you won't be able to resist buying new baby socks for brand new toys.
If you're a crafts fan, you can also knit or crochet cute "mice" to hold your home-grown dried catnip, using one of the patterns I collected in my Arts and Crafts resource page.
Whether "store-bought" or created at home, catnip toys will provide hours of enjoyment for you and your cats.