Paranoia is a term used to describe feelings of suspicion or mistrust by an individual that are either highly exaggerated or completely unwarranted. For example, people with paranoia may believe that others are plotting against them. People who are paranoid often have feelings of exaggerated sense of self-importance and believe that they are persecuted by others.

Medical conditions can cause paranoia. Paranoia is also a feature of many mental health conditions, but is most prominent in four disorders:

• Paranoid personality disorder. Condition in which a person regularly becomes suspicious without cause.
  
  
• Delusional (paranoid) disorder (persecutory type). Condition that involves persistent, nonbizarre delusions (delusions about situations that may occur in real life, such as being followed, poisoned or deceived by a spouse or lover). Delusions are beliefs that an individual holds that are not true, not shared by others in a culture and cannot be easily modified.
  
  
• Paranoid schizophrenia. Condition marked by extremely bizarre delusions or hallucinations that are almost always based on a specific theme.
  
  
• Substance abuse and dependence.  Paranoia is associated with the use of many substances, most prominently alcohol, cocaine, steroids and amphetamines.   

People who are paranoid may manifest several other related symptoms. Continual mistrust and suspicion are closely associated with paranoia, as are hypersensitivity and a tendency to be emotionally cold or aloof.