It's not addictive and yeah, I have heard it called marijuana for cats! My mom always says our Siamese cat looks high when he's playing with it! I only give it to my cats once in a while....if they have access to it all the time they lose interest. It grows outside in our garden in the summer so when I was at home I always took my Siamese cat and picked some fresh stuff to bring in for the rest of the cats. All cats react differently. It affects my Siamese for a short amount of time, my old female just eats it, and my younger cat Murphy goes CRAAAAZY for it!
I haven't tried it with my kitten yet cause he is only 14 weeks old and I doubt it would affect him much yet.
But no, it's totally safe as long as it doesn't have an pesticides on it or anything. I always wash the fresh stuff anyway before I give it to them. I get a funnier reaction from them though if they don't get it too often.