Paranoia is not always due to a mental illness. Recent studies have shown that mild paranoid thoughts are fairly common in the general population.
People become paranoid when their ability to reason and assign meaning to things breaks down. We don’t know why this happens. It’s thought paranoia it could be caused by genes, chemicals in the brain or by a stressful or traumatic life event. It’s likely a combination of factors is responsible.
Mental disorders that cause paranoia include:
Paranoid personality disorder
A personality disorder is a long-standing pattern of problematic thoughts, feelings and behaviour. People with paranoid personality disorder have a tendency to assume that others will harm, deceive or take advantage of them. They may appear secretive, argumentative or cold and be difficult to get along with. This disorder is uncommon and usually improves with age so that many people recover by their 40s or 50s.
People with a delusional disorder have one delusion (a fixed, false belief) without any other symptoms of mental illness. Paranoid delusions are the most common, making people feel there is a conspiracy or they are going to be harmed. But people with a delusional disorder can also have other types of unusual beliefs.
Schizophrenia is a form of psychosis and causes people to have trouble interpreting reality. The main symptoms are hallucinations (such as hearing voices that aren’t there) and delusions (fixed, false beliefs). Some people with schizophrenia have bizarre delusions such as believing that their thoughts are being broadcast over the radio or they are being persecuted by the government. Other symptoms include confused thinking and reduced motivation for everyday tasks.
Psychotic disorder and bipolar disorder can cause paranoia.
Other causes of paranoia include:
- Recreational drug use: Cannabis and amphetamine abuse often causes paranoid thoughts and may trigger an episode of psychosis. Other drugs such as alcohol, cocaine and ecstasy can also cause paranoia during intoxication or withdrawals.
- Neurological disease: Diseases such as dementia (including Alzheimer’s disease), Huntington’s disease, Parkinson’s disease or brain injury can cause paranoia.
- Severe trauma and stress: Some studies have found that paranoia is more common in people who have experienced severe and ongoing stress. This may include abuse in childhood, domestic violence, racial persecution or living in isolation.
Last reviewed: December 2018