The causes of psychosis have three main classifications:
- psychosis that is caused by psychological (mental) conditions
- psychosis that is caused by general medical conditions
- psychosis that is caused by substances, such as alcohol or drugs
These three classifications are described in more detail below.
Psychological causes
The following conditions have been known to trigger psychotic episodes in some people:
- schizophrenia – a chronic (long-term) mental health condition that causes hallucinations and delusions
- bipolar disorder – previously called manic depression, bipolar disorder affects your moods, which can swing from one extreme to another
- severe stress or anxiety
- severe depression – feelings of extreme sadness that last for a long time (including postnatal depression, which some women experience after having a baby)
- lack of sleep
The underlying psychological cause will often influence the type of psychotic episode that someone experiences. For example, a person with bipolar disorder is more likely to have delusions of grandeur, whereas someone with depression or schizophrenia is more likely to develop paranoid delusions (see Psychosis – Symptoms).
General medical conditions
The following medical conditions have been known to trigger psychotic episodes in some people:
- HIV and AIDS – a virus that attacks the body's immune system (the body’s natural defence against illness and infection)
- malaria – a tropical disease that is spread by infected mosquitoes
- syphilis – a bacterial infection that is usually passed on through sexual contact
- Alzheimer's disease – the most common form of dementia that causes a decline of mental abilities, such as memory and reasoning
- Parkinson's disease – a chronic condition that affects the way the brain co-ordinates body movements, including walking, talking and writing
- hypoglycaemia – an abnormally low level of sugar (glucose) in the blood
- lupus – a condition where your immune system attacks healthy tissue
- Lyme disease – a bacterial infection that is spread to humans by infected ticks
- multiple sclerosis – a condition of the central nervous system (the brain and spinal cord)
- brain tumour – a growth of cells in the brain that multiply in an abnormal and uncontrollable way
Substances
Drug misuse can trigger a psychotic episode. A psychotic episode can also be triggered if you suddenly stop taking a drug after using it for a long time. This is known as drug withdrawal. Drugs that are known to trigger psychotic episodes include:
- alcohol
- cocaine
- amphetamine (speed)
- methamphetamine (crystal meth)
- MDMA (ecstasy)
- cannabis
- LSD (acid)
- psilocybins (magic mushrooms)
- ketamine
In rare situations, psychosis can also occur as a side effect of some types of medication, or as a result of an overdose of that medication. These medications include:
- tranquillisers, such as barbiturates or benzodiazepines
- anti-epileptic medication
- antidepressants
- anticholinergic medications – medicines that are often used to help open up the airways
- levodopa – a medication that is used to treat Parkinson's disease
Never stop taking a prescribed medication unless you are advised to do so by your GP or another qualified healthcare professional who is responsible for your care. See your GP if you are experiencing psychotic side effects because of taking a medication.
Grey matter
Research has revealed that during a psychotic episode several physical and biological changes occur in the brain.
The results of magnetic resonance imaging (MRI) scans of the brains of people with a history of psychosis showed that they had less grey matter than other people. Grey matter is the part of the brain that is responsible for processing thoughts. MRI scans use a strong magnetic field and radio waves to take images of the inside of the body.
The result of this research has led to some researchers suggesting that repeated episodes of psychosis may actually cause physical damage to the brain. However, further research is required to confirm this.
Alternatively, both the reduction of grey matter and a history of psychosis could both be symptoms of an underlying condition that has not yet been identified.
Dopamine
Researchers also believe that dopamine plays an important role in psychosis.
Dopamine is a neurotransmitter, which is one of many chemicals that the brain uses to transmit information from one brain cell to another. Dopamine is associated with feelings of pleasure and reward. For example, when you experience an enjoyable or pleasurable event, such as sex, the levels of dopamine in your brain increase.
In people with psychosis, it is thought that the levels of dopamine in their brain become too high. The excess dopamine interrupts the specific pathways of the brain that are responsible for some of its most important functions, such as:
- memory
- emotion
- social behaviour
- self-awareness
The disruption to these important brain functions may explain the symptoms of psychosis.
The evidence for the role of dopamine in psychosis is that medications that are known to reduce the effects of dopamine in the brain also reduce the symptoms of psychosis. However, illegal drugs that are known to increase the levels of dopamine in the brain, such as cannabis, cocaine and amphetamines, can trigger psychosis.
