This drug like feeling doesn't affect all cats the same. About 66% are affected by it, some, usually small male kittens will become very aggressive and hyper which could be tough to handle. Kittens usually don't feel the effects since they are not sexually matured yet. Swallowing or eating catnip is not dangerous for your cat but does have reverse effects which may put your cat asleep.
It isn't addictive and could be used to stimulate your cat in practicing good behaviors, for example rubbing catnip on a scratching post to lure him to use it more often. You can also buy fresh grained catnip and put it in a pocket of a toy to keep it entertained. The scent of catnip does diminish so keeping it in the freezer will preserve it longer. You should also ratio how much your feline plays with catnip so that they stay stimulated by it.
Do not be afraid to test some catnip on your cat, people have a bad misconception about it because it is a drug but it is not harmful or addictive. If your cat is stimulated by it, it can revitalize old games or start new ones. Its no different than giving them a treat.