I have quite a lot of catnip bushes in my garden, thus my cats have an eat as much as you can catnip buffet anytime they wish to. They love to roll around in the catnip to make themselves smell like it.
I never had any problems with my cats getting aggressive on catnip, they usually go lovey dovey on me when they eat it. The quiet one sometimes becomes a little vocal and she tells me about her whole day.
It might be that dried catnip are more potent than fresh catnip, and may cause this aggression.Try some fresh catnip and compare the results of your findings. use the one that have the least negative effects.