Mine eat it too. They roll on their backs and act weird, and then they sleep. I have tried leaving a sprig in their bed, but they always dig it out and eat it within minutes. Last year I got a little tiny catnip plant and put it in my flower garden. Now that little plant is a huge bush, and it looks like a weed. Smells nice though. I tried eating a leaf, but the liquid in it tastes bad to me, and the fiber is tough. It's good in an herbal tea mixed with mint and other herbs though. I would say it's probably a hypnotic. Has some sedative properties, anyway, for people too, but not as strong as for cats. I planted it in a different garden from my mind so that I could tell them apart. They look alike and smell similar. But the mint is sweeter and doesn't get so big (although it spreads).

They say 30% of cats are immune to catnip. My black cat didn't care about it at first, but he acquired a taste for it, and no matter how much of the stuff is available, the two cats will fight over it, and it will be gone by morning. My dogs will eat it too sometimes, but I think just because the cats are eating it.