By "various substances" do you mean properly prescribed medication or recreational drugs? Seeing a doctor and getting some proper meds for it would probably be helpful if you're not already doing that. Talking to a psychologist would help too, but being paranoid makes it very hard to trust them enough to reveal your inner thoughts to them.
I used to have a mild paranoid delusion that each time I left the house I was being put under surveillance by some kind of organised group. I'd count the seconds between each time I was within view of another person (passing cars, windows in houses, people walking along the street) and thought that they were conspiring to keep watching me and make sure I didn't leave their sight for more than a certain number of seconds, and that they were doing so because I was part of some kind of experimental study on people in our sort of situation. After I was put on an anti-psychotic the thoughts gradually went away and now to think of them and realise how dumb I was being is really embarrassing.
General trust issues with people you know are probably a lot harder to deal with though. I guess on way to help with those is to think about what it is you can't trust them with. Are you worried about them finding out something about you and not liking you because of it? Or worried about them telling other people secrts about you? The only way I've found to deal with those thoughts is to automatically assume people already have the lowest possible opinion of you, and so nothing that you can do or they can find out about you will make things any worse, and so there's nothing to worry about. It's not much of a solution though, more like accepting defeat without even trying. Sorry, I guess it's not a very helpful solution for feeling any better around people.