The causes of psychosis are complex and researchers are still trying to understand them fully. However, psychosis is thought to be caused by an interaction between genetic and environmental factors. It's likely that some people are born with a predisposition to develop this kind of illness and that certain things - for example, stress or the use of drugs such as marijuana, LSD or speed or medications — can trigger their first episode.

The main categories of causes of psychosis are:

• mental illness: psychosis can be caused by a mental illness, such as schizophrenia, bipolar disorder, or severe depression.
• genetics: people with a family history of psychotic disorders such as schizophrenia have a slightly increased chance of developing psychosis. There is no single gene that causes psychosis, but a number of different genes may increase the likelihood of developing it.
• recreational drugs: psychosis can be triggered by the use of drugs, including cannabis, amphetamines (including speed and ice), LSD (acid), magic mushrooms, ketamine, ecstasy and cocaine.

Can medical conditions cause psychosis?

Some medical conditions have been known to cause psychosis, although this is rare. These include:

• head injuries
• HIV and AIDS
• malaria or taking malaria medications
• syphilis
• Alzheimer’s disease and Lewy body dementia
• Parkinson’s disease
• lupus
• Lyme disease
• postnatal depression
• multiple sclerosis
• stroke
• some types of epilepsy
• brain tumours
• some types of hormone disorders
• some dietary deficiencies

There’s also research showing that too much dopamine may be associated with psychosis. Dopamine is one of the chemicals in the brain that sends information from one brain cell to another. Having high levels could interrupt the pathways in the brain responsible for memory, emotion, social behaviour and self-awareness.

Although the causes are still being uncovered, psychosis is treatable. With medicine and support, people with psychosis can recover from their illness.