catnip given in moderate amounts is not only not harmful to cats it can be beneficial. my mom gives her elderly cat fresh catnip to ease arthritic pain. i wouldnt give catnip to cats at night or you may have difficulty sleeping. it helps obese cats become more active. we feed a treat i think is called natures delight or something like it and it has real catnip in it. we feed this maybe a few times a week and in small amounts. say about 4 kibbles per cat. remember that to much of anything is never good.