adj
believing unreasonably that you cannot trust other people, or that they are trying to harm you or have a bad opinion of you
be/become/get paranoid
　Malcolm got really paranoid, deciding that there was a conspiracy out to get him.
paranoid about
　He has always been paranoid about his personal security.
medical suffering from a mental illness that makes you believe that other people are trying to harm you
　a patient suffering from paranoid schizophrenia