What causes it?
Paranoia can be caused by a number of factors such as stressful life events, but it is most commonly seen in people with mental health problems and people using street drugs. Drugs such as amphetamine, cannabis, cocaine, ecstasy and LSD often cause bad trips, where users feel paranoid for a time, but long-term or heavy drug users can experience more serious problems with paranoia that are not easily shaken off.
People experiencing severe anxiety or depression can develop problems with paranoid feelings, but the most extreme forms of paranoia are usually seen in people diagnosed with schizophrenia or manic depression. These illnesses can cause people to lose touch with reality, a feature known as psychosis, so that when people develop paranoia they frequently lose the insight to recognise that their fears are not grounded in reality.