What Causes Psychosis?

Mental health care

There are many causes of psychosis and often it might not be possible to pinpoint an exact reason why an individual has a psychotic episode. At some point in their lives, about 3% of people will experience psychosis. It will typically begin to affect people as they reach their late teens or early twenties and, although it affects both men and women in equal measure, men typically experience symptoms younger than women.

Psychosis does run in families and if a family member experiences psychosis, others are more susceptible, especially if a family member has a personality disorder such as paranoid personality disorder or a psychotic disorder like schizophrenia.

Dopamine and other brain chemicals

Science has shed some light on the chemical causes of psychosis. Dopamine, a neurotransmitter in the brain is at play in psychosis. This brain chemical helps to control how information flows in the brain. It is one of many brain chemicals whose function is to transmit information between brain cells. Dopamine is associated with feeling that something is interesting, important or significant. If dopamine is in abundance, then the brain seeks to take in lots of information – more than it can realistically handle. If there isn’t enough dopamine, the brain responds differently and creates a slowness and problems with muscles in the body, not dissimilar to Parkinson’s disease. A disruption in dopamine function goes some way in explaining psychosis symptoms.

As far as psychosis is concerned, there is research to suggest that there is too much dopamine in individuals with psychosis and that the constant flood of information into the brain is simply too overwhelming. When it comes to treating psychosis, the medications used are often ones that help to control how much dopamine is in the brain.

Childhood trauma and adversity

Throughout the last ten or so years, there have been a large number of population-based studies that suggest that trauma in childhood is a contributing factor in psychosis. In some studies, these effects still stood even after adjustments were made to a variety of confounding variables, including a genetic predisposition to psychosis. Not a lot is known about the underlying mechanisms that cause the association between trauma in childhood and psychosis but possible pathways are negative perceptions of the self and relationships, negative affect, psychotic symptoms and biological mechanisms like increased sensitivity to stress and dysregulated cortisol. Patients with psychosis that have childhood trauma in their background will usually present with a range of additional problems like PTSD (post-traumatic stress disorder), substance abuse, anxiety, depression and suicide attempts that are more frequent.


Stress can cause psychosis, however, it is normally only a trigger for people who already have an underlying vulnerability, though not always. When intense stress causes psychosis there might not be any other diseases or conditions involved. Usually, this type of psychosis will typically last for a month or less.

During a psychotic episode, an individual’s brain is suffering from stress overload. Stress has many causes including bereavement, trauma, poor physical health or major life events and changes. When an individual is under frequent stress, their body can be affected both mentally and physically. If an individual’s brain is no longer able to process stress effectively, information and emotion processing becomes affected, which results in difficulties perceiving reality. Therefore, it is vital that individuals listen to their bodies and manage their stress levels. Despite managing stress well, some individuals will still have psychotic episodes.

City life, migration and social adversity

Recently, there has been lots of research undertaken on the incidence of psychoses and schizophrenia with regards to geographical variation. Recent studies have shown than urbanicity does have an association with more frequent incidences of non-affective psychosis and schizophrenia. What’s more, there has been shown to be a significant variation between different neighbourhoods.

The findings of this research suggest that it is unlikely for these geographical variations to be caused solely by social drift. There is further evidence to suggest that there is an impact from the adverse social context, for example, social fragmentation, population density and deprivation. But this is modified by individual environmental exposures such as discrimination, exclusion, social adversity and cannabis use). When we look at things from a neurobiological perspective, there are several studies that recognise a link between stress, isolation and social adversity and monoamine dysfunction, a cause of depression but there aren’t any studies that recognise a link between these and psychosis as of yet.

How geography affects incidences of psychosis

Studies on the incidence of psychoses and schizophrenia in relation to geographical variation have been conducted since the 1920s. The first studies were in Chicago and Bristol.

The Chicago study, by Faris and Dunham, was the first to find a higher rate of admissions for schizophrenia in the city centre. What’s more, the rate of schizophrenia was less the further away from the city centre you looked at. The rates of schizophrenia didn’t follow the pattern of the rates of other conditions classed as affective psychosis (i.e. bipolar disorder and psychotic depression). The incidence of these conditions was spread more evenly throughout both peripheral and central areas. To add more fuel to this work, there were similar findings in nine different cities across the United States.

The brain

Aside from the physical changes with dopamine and brain chemicals, the brain can be responsible for the psychological causes of psychosis. There are known medical conditions that trigger psychotic episodes in individuals:

  • Bipolar disorder – an individual with bipolar disorder can have episodes of elated or high moods (mania) and episodes of low mood (depression)
  • Schizophrenia – this is a mental illness that causes delusion and hallucinations
  • Severe depression – this means that an individual has feelings of persistent sadness and also includes postnatal depression that some women will experience after giving birth
  • Lack of sleep

Where there is an underlying psychological cause to psychosis, this will also affect the type of psychotic episode an individual experiences. For example, an individual with schizophrenia or depression will be more likely to have persecutory delusions whereas someone with bipolar disorder will be more likely to experience grandiose delusions.

Birth Complications

Birth complications were first mooted as a factor for psychosis during the 1930s yet the first studies in adults didn’t happen for a further thirty years. The results of these early studies were inconsistent due to methodological issues. Later studies showed significant links between ten complications and schizophrenia. These ten complications were grouped into separate categories.

One category was related to pregnancy complications and included rhesus compatibility, diabetes, preeclampsia and bleeding, another category was abnormal fetal development and grown and included low birth weight, small head circumference and congenital malformations and the final category was delivery complications and included emergency caesarean section, uterine atony and asphyxia. Although there were associations found, the effect sizes were pretty small. Consequently, it is more likely that birth complications contribute to psychosis when there is a combination of other risk factors at play, for example, genetic predispositions. These small associations do seem larger when there is an early onset of the illness. These links are not yet fully understood. Some researchers have found that adults and adolescents who were born with very low birth weight or who were very premature, have similar abnormalities in their brains as individuals with schizophrenia. Such abnormalities include lateral ventricular enlargement.

Cannabis and other drugs

A British newspaper, The Guardian, reported recently that high-strength cannabis increases an individual’s risk of developing mental health problems. In fact, it is estimated that individuals using high-strength cannabis have a five-fold risk increase of having a first psychotic episode. The strength of cannabis is based upon how much tetrahydrocannabinol (THC), the active ingredient, is in it. Cannabis resin (also known as hashish) and cannabis in traditional herb form usually contain less than 10% THC. Skunk, or high-strength cannabis, might have a THC content of up to 67%. The study that found the link between cannabis use and mental health problems looked at how cannabis was used (e.g. which type was used and how often it was used) in sixteen areas across Europe and one area of Brazil.

The results were used in conjunction with the incidences of psychosis to determine the effect the use of cannabis could have on the occurrence of psychosis. The researchers learnt that it was common in both Amsterdam and London to use high-strength cannabis on a daily basis and that this was a possible factor in around 30% of first psychotic episodes in London and as much as 50% of first psychotic episodes in Amsterdam every year.

Of course, it isn’t a certainty that cannabis use was the causal factor in psychosis for every study participant but these findings must be seriously considered. The researchers also discovered that using high-strength cannabis on a daily basis was linked to five-fold risk of experiencing a psychotic episode when compared with individuals who didn’t use cannabis at all.

Other drugs and substances

Any misuse of drugs or alcohol can cause a psychotic episode. It isn’t just the ingestion of drugs or alcohol that can trigger a psychotic episode. It is also possible for a psychotic episode to occur when alcohol or drug use is stopped after a long time of use. In other words, withdrawing from drug use and alcohol use can cause an individual to experience psychosis as can drinking alcohol in excess or being high on drugs.

There are a number of drugs that have a known causal link with psychosis. These include:

  • Amphetamine (speed)
  • Cannabis
  • Cocain
  • Ketamine
  • LSD (acid)
  • MDMA (ecstasy)
  • Mephedrone (miaow or MCAT)
  • Methamphetamine (crystal meth)
  • Psilocybins (magic mushrooms)

Rarely, psychosis can be a side effect of medications taken regularly or as the result of overdosing. It is important, though, to not stop taking a medication that is prescribed unless otherwise advised by a healthcare professional who is responsible for your care. It goes without saying that you should

Other possible factors

There are some general medical conditions that have been known to cause psychotic episodes as side effects in some people. These include:

  • Alzheimer’s disease
  • Auditory or visual nerve damage
  • Autoimmune disorders
  • Brain tumours or traumatic brain injury
  • Central nervous system infections
  • Cerebrovascular disease
  • Epilepsy
  • Huntington’s disease
  • Hypoglycemia (abnormally low levels of blood glucose, often seen in diabetics)
  • HIV and AIDS
  • Lupus
  • Malaria
  • Migraine headache
  • Multiple sclerosis
  • Parkinson’s disease
  • Stroke
  • Syphilis
  • Thyroid disease

It is speculated that patients with medical conditions might have autoimmune or inflammatory disorders that play a role in psychosis as well as their medical condition. It could also be that the disorders are influenced by an individual’s predisposition to psychosis and the medical condition. To give an example, around 7% of people with epilepsy have experienced an episode of psychosis.

It must also be mentioned that having symptoms of psychosis also puts an individual at risk of comorbid medical problems and risky behaviours with regards to lifestyle.


The most recent research into the causes of psychosis place a combination of circumstances, genetics and environment putting an individual more at risk of experiencing a psychotic episode. In a person with a genetic predisposition, stress has been discovered to be an important player in an individual’s chances of experiencing psychosis. More often than not, serious events (like surgery or family death) or big life changes (such as changing jobs or starting university) will trigger an individual’s first symptoms of a psychotic episode.