I was going to the city today to go buy a diffuser to see if that helps. The question I have is; it says it is like the hormone or whatnot that is released from a glad on a cats head..... if I get this, will it eventually take the ability of my cat to produce that hormone?
Basically how it works is that when a cat rubs is head against things they're marking it. They deposit a pheromone that makes them feel safe and comfortable when they sense it around them. The feliway gives off that same pheromone (only generalized to work for all cats, i.e make them feel like it's theirs) So really you can see it as you humans doing your part in scent marking the home to making your cat feel comfortable.
It's not a drug and it shouldn't affect your cat in any way other than making him feel more relaxed and feel more in control of his territory so maybe he won't freak out as much when he sees strange cats through the window.
It can also help in multiple cat homes, all the cats think that the extra scent marking is theirs so they all feel happier.
Also cats rub their heads to mark their core area, they scratch and spray to mark the fringe areas so the feliway can help stop spraying cats and cats that scratch for territory marking reasons by making them feel that the whole house has already been marked and is a core territory.
It doesn't work on every single cat, some are immune and a very small fraction registers the feliway as if the pheromones given off are from another cat and then start up with more territory marking. This is very very rare though. If that happens just stop the diffuser and you should be back to normal (strange cat has been driven off from your cats point of view)