Catnip?

My cat Inky is 11 years old and very overweight (we're working on that though, and I'll most likely be bombarding the forum with more questions regarding that). One of the biggest problems is that he doesn't like to get exercise. The bulk of his exercise comes from running to either the food bowl or to get petted and fussed over.

He will swat at, bite, and "attack" a thick shoelace if I dangle it in front of him, but he loses all interest if he actually has to get up to chase it
He's never had catnip before, and I was wondering if that usually makes them more energetic or more eager to play?
Also, how often is it safe to give a cat catnip?

Thanks in advance

(I wasn't sure if this was the right section to post this or not, feel free to move it)

Catnip is not addictive thou some can get burn out...

I sprinkle nip a few time s a week ...

okay, thank you