Psychosis can be caused by a mental (psychological) condition, a general medical condition, or alcohol or drug misuse.
Psychological causes
The following conditions have been known to trigger psychotic episodes in some people:
- schizophrenia – a mental health condition that causes hallucinations and delusions
- bipolar disorder – a person with bipolar disorder can have episodes of low mood (depression) and highs or elated mood (mania)
- severe stress or anxiety
- severe depression – feelings of persistent sadness, including postnatal depression, which some women experience after having a baby
- lack of sleep
The underlying psychological cause often influences the type of psychotic episode someone experiences.
For example, a person with bipolar disorder is more likely to have grandiose delusions. Someone with depression or schizophrenia is more likely to develop persecutory delusions.
See symptoms of psychosis for more information on delusions.
General medical conditions
The following medical conditions have been known to trigger psychotic episodes in some people:
- HIV and AIDS
- malaria
- syphilis
- Alzheimer's disease
- Parkinson's disease
- hypoglycaemia (an abnormally low level of glucose in the blood)
- lupus
- multiple sclerosis
- brain tumour
- sudden illness or injury, such as a high temperature or a head injury
Substances
Alcohol misuse and drug misuse can trigger a psychotic episode.
A person can also experience a psychotic episode if they suddenly stop drinking alcohol or taking drugs after using them for a long time. This is known as withdrawal.
It's also possible to experience psychosis after drinking large amounts of alcohol or if you're high on drugs.
Drugs known to trigger psychotic episodes include:
- cocaine
- amphetamine (speed)
- methamphetamine (crystal meth)
- mephedrone (MCAT or miaow)
- MDMA (ecstasy)
- cannabis
- LSD (acid)
- psilocybins (magic mushrooms)
- ketamine
Medicine
In rare situations, psychosis can also occur as a side effect of some types of medicine or as a result of an overdose of that medicine.
Never stop taking a prescribed medicine unless advised to do so by a GP or another qualified healthcare professional responsible for your care.
See a GP if you're experiencing psychotic side effects caused by medicine.
The brain
There's been a great deal of research into how psychosis affects the brain and how changes in the brain can trigger symptoms of psychosis.
It’s thought psychosis may be linked to increased activity of neurotransmitters in the brain.
Neurotransmitters, like dopamine, are chemicals that help send information inside the brain.
Evidence for the role of dopamine in psychosis comes from the fact medicines known to reduce the effects of dopamine in the brain also reduce the symptoms of psychosis.