Psychosis is a generic psychiatric term for mental states in which the components of rational thought and perception are severely impaired. Persons experiencing a psychosis may experience hallucinations, hold paranoid or delusional beliefs, demonstrate personality changes and exhibit disorganized thinking (see thought disorder). This is usually accompanied by features such as a lack of insight into the unusual or bizarre nature of their behavior, difficulties with social interaction and impairments in carrying out the activities of daily living. Essentially, a psychotic episode involves loss of contact with reality, sometimes termed "loss of reality testing."


Psychosis is usually considered by mainstream psychiatry to be a symptom of severe mental illness. Although it is not exclusively linked to any particular psychological or physical state, it is particularly associated with schizophrenia, bipolar disorder (manic depression) and severe clinical depression. There are also several physical circumstances that can induce a psychotic state, including electrolyte disorder, urinary tract infections in the elderly, pain syndromes, drug toxicity, and drug withdrawal (especially alcohol, barbiturates, and sometimes benzodiazepines), as well as infections of or injuries to the brain (these psychoses are now more commonly referred to as organic mental disorders).

It is not uncommon in cases of brain injury and may occur after drug use, particularly after drug overdose, chronic use, and during drug withdrawal. Certain compounds may be more likely to induce psychosis, and some individuals may show greater sensitivity than others. Drugs can induce true psychosis two ways, due to drug intoxication, or due to drug withdrawal. Anticholinergic drugs (atropine, scopolamine, cortisone Jimson weed, most antihistamines (diphenhydramine, dimenhydrinate, hydroxizine, etc)) can induce a true psychotic state which will abate once the acute effects of the drug wear off. So, of course, can certain "street" drugs such as PCP, cocaine, amphetamines and hallucinogens.

Drugs that have general depressant effects on the central nervous system, especially alcohol and barbiturates, do not induce psychosis during use, and actually can decrease psychotic symptoms, but withdrawal from them induces a state of hyperactivity that is indistinguishable from psychosis. The withdrawal from barbiturates and alcohol can be particularly dangerous as not only is there a severe impairment of reality testing with acting out on psychotic delusions, there is a possibly mortal effect upon the body.

Chronic psychological stress is also known to cause psychotic states; however, the exact mechanism is uncertain. Short-lived pychosis triggered by stress is known as brief reactive psychosis.

The term psychosis should be distinguished from the concept of insanity, which is a legal term denoting that a person should not be criminally responsible for his actions. Similarly, it should be distinguished from psychopathy, a personality disorder often associated with violence, lack of empathy and socially manipulative behaviour. Despite the fact that both are colloquially abbreviated to 'psycho', psychosis bears little similarity to psychopathy's core features, particularly with regard to violence, which rarely occurs in psychosis, and the distortion of perceived reality, which rarely occurs in psychopathy.

It should also be distinguished from the state of delirium, in that a psychotic individual may be able to perform actions that require a high level of intellectual effort in clear consciousness. Finally, it should be distinguished from mental illness. Psychosis may be regarded as a symptom of other mental illnesses, but as a descriptive concept it is not considered an illness in its own right. For example, persons with schizophrenia can have long periods without psychosis, and persons with bipolar disorder and depression can have mood symptoms without psychosis. Conversely, psychosis can occur in persons without chronic mental illness as a result of an adverse drug reaction or extreme stress.

During the 1960s and 1970s, psychosis was of particular interest to counterculture critics of mainstream psychiatric practice who argued that it may simply be another way of constructing reality and is not necessarily a sign of illness. For example, R. D. Laing argued that psychosis is a symbolic way of expressing concerns in situations where such views may be unwelcome or uncomfortable to the recipients. Thomas Szasz focused on the social implications of labelling people as psychotic; a label which he argues unjustly medicalises different views of reality so such unorthodox people can be controlled by society. Scientology has repudiated the concept completely.

Generally, however, advances in both differential diagnosis and studies of the biochemistry of psychotic and non-psychotic individuals has established that there are usually underlying, physical causes (not always yet well understood) for the appearance of a psychosis, and that psychotropic intervention can effectively minimize or eliminate the symptomatology within a relatively rapid amount of time, restoring without altering the patient's usual interests, ambitions, dreams, skills, talents and ability to safely conduct his/her daily life. In the United States and Europe, few reputable practitioners, since the 1990s, have approached psychosis outside this scientific frame of reference.

Etymology - The word psychosis was first used by Ernst von Feuchtersleben in 1845 as an alternative to insanity and mania and stems from the Greek psykhe (mind) and osis (diseased or abnormal condition). The word was used to distinguish disorders which were thought to be disorders of the mind, as opposed to neurosis, which was thought to stem from a disorder of the nerves.

Psychotic experience

A psychotic episode can be significantly coloured by mood. For example, people experiencing a psychotic episode in the context of depression may experience persecutory or self-blaming delusions or hallucinations, whilst people experiencing a psychotic episode in the context of mania may form grandiose delusions or have an experience of deep religious significance.

Although usually distressing and regarded as an illness process, some people who experience psychosis find beneficial aspects and value the experience or revelations that stem from it.


Hallucinations are defined as sensory perception in the absence of external stimuli. Psychotic hallucinations may occur in any of the five senses and take on almost any form, which may include simple sensations (such as lights, colours, tastes, smells) to more meaningful experiences such as seeing and interacting with fully formed animals and people, hearing voices and complex tactile sensations.

Auditory hallucinations, particularly the experience of hearing voices, are a common and often prominent feature of psychosis. Hallucinated voices may talk about, or to the person, and may involve several speakers with distinct personas. Auditory hallucinations tend to be particularly distressing when they are derogatory, commanding or preoccupying. However, the experience of hearing voices need not always be a negative one, as outlined by the Hearing Voices Movement informed by the research of Prof. Marius Romme.

Delusions and paranoia

Psychosis may involve delusional or paranoid beliefs. Karl Jaspers classified psychotic delusions into primary and secondary types. Primary delusions are defined as arising out-of-the-blue and not being comprehensible in terms of normal mental processes, whereas secondary delusions may be understood as being influenced by the person's background or current situation.

Thought disorder

Thought disorder describes an underlying disturbance to conscious thought and is classified largely by its effects on speech and writing. Affected persons may show pressure of speech (speaking incessantly and quickly), derailment or flight of ideas (switching topic mid-sentence or inappropriately), thought blocking, rhyming or punning.

Lack of insight

One important and puzzling feature of psychosis is usually an accompanying lack of insight into the unusual, strange or bizarre nature of the person's experience or behaviour. Even in the case of an acute psychosis, sufferers may seem completely unaware that their vivid hallucinations and impossible delusions are in any way unrealistic. This is not an absolute; however, insight can vary between individuals and throughout the duration of the psychotic episode.

In some cases, particularly with auditory and visual hallucinations, the patient has good insight and this makes the psychotic experience even more terrifying in that the patient realizes that he should not be hearing voices, but does.

Medical understanding of psychosis

There are a number of possible causes for psychosis. Psychosis may be the result of an underlying mental illness such as Bipolar disorder (also known as manic depression), and schizophrenia. Psychosis may also be triggered or exacerbated by severe mental stress and high doses or chronic use of drugs such as amphetamines, LSD, PCP, cocaine or scopolamine. However, incidence of psychosis resulting from a single administration of any drug is rare, although cases have been reported in the medical literature suggesting a person's sensitivities to new compounds can be unpredictable. Sudden withdrawal from CNS depressant drugs, such as alcohol and benzodiazepines, may also trigger psychotic episodes. As can be seen from the wide variety of illnesses and conditions in which psychosis has been reported to arise (including for example, AIDS, leprosy, malaria and even mumps) there is no singular cause of a psychotic episode.

The division of the major psychoses into manic depressive insanity (now called bipolar disorder) and dementia praecox (now called schizophrenia) was made by Emil Kraepelin, who attempted to create a synthesis of the various mental disorders identified by 19th-century psychiatrists, by grouping diseases together based on classification of common symptoms. Kraepelin used the term 'manic depressive insanity' to describe the whole spectrum of mood disorders, in a far wider sense than it is usually used today. In Kraepelin's classification this would include 'unipolar' clinical depression, as well as bipolar disorder and other mood disorders such as cyclothymia. These are characterised by problems with mood control and the psychotic episodes appear associated with disturbances in mood, and patients will often have periods of normal functioning between psychotic episodes even without medication. Schizophrenia is characterized by psychotic episodes which appear to be unrelated to disturbances in mood, and most non-medicated patients will show signs of disturbance between psychotic episodes.

Psychotic episodes may vary in duration between individuals. In brief reactive psychosis, the psychotic episode is related directly to a specific stressful life event, so patients may spontaneously recover normal functioning within two weeks. In some rare cases, individuals may remain in a state of full-blown psychosis for many years, or perhaps have attenuated psychotic symptoms (such as low intensity hallucinations) present at most times.

Patients who are undergoing a brief psychotic episode may have many of the same symptoms as a person who is psychotic as a result of (for example) schizophrenia, and this fact has been used to support the notion that psychosis is primarily a breakdown in some specific biological system in the brain. The dopamine hypothesis of psychosis was an early, and still popular, example of a theory based on this assumption. However, it is controversial how much weight should be given to such exclusively biological theories as it has become clearer that a wide range of influences (including environmental, social and childhood development factors) may contribute to the final experience of psychosis.

It has also been argued that psychosis exists on a continuum as everybody may have some unusual and potentially reality-distorting experiences in their life. This has been backed up by research showing that experiences such as hallucinations have been experienced by large numbers of the population who may never be impaired or even distressed by their experiences10. In this view, people who are diagnosed with a psychotic illness may simply be one end of a spectrum where the experiences become particularly intense or distressing (see schizotypy).

Psychosis and brain function

The first brain image of person with psychosis was completed as far back as 1935 using a technique called pneumoencephalography1 (a painful and now obsolete procedure where cerebrospinal fluid is drained from around the brain and replaced with air to allow the structure of the brain to show up more clearly on an X-ray picture).

Pneumo-encephalogram of person with psychosis, 1935Modern brain imaging studies, investigating both changes in brain structure and changes in brain function of people undergoing psychotic episodes, have shown mixed results.

A 2003 study investigating structural changes in the brains of people with psychosis showed there was significant grey matter reduction in the cortex of people before and after they became psychotic2. Findings such as these have led to debate about whether psychosis is itself neurotoxic and whether potentially damaging changes to the brain are related to the length of psychotic episode. Recent research has suggested that this is not the case3 although further investigation is still ongoing.

Functional brain scans have revealed that the areas of the brain that reacts to sensory perceptions are active during psychosis. For example, a PET or fMRI scan of a person who claims to be hearing voices may show activation in the auditory cortex, or parts of the brain involved in the perception and understanding of speech.

On the other hand, there is not a clear enough psychological definition of belief to make a comparison between different people particularly valid. Brain imaging studies on delusions have typically relied on correlations of brain activation patterns with the presence of delusional beliefs.

One clear finding is that persons with a tendency to have psychotic experiences seem to show increased activation in the right hemisphere of the brain4. This increased level of right hemisphere activation has also been found in healthy people who have high levels of paranormal beliefs5 or in people who report mystical experiences6. It also seems to be the case that people who are more creative are also more likely to show a similar pattern of brain activation7. Some researchers have been quick to point out that this in no way suggests that paranormal, mystical or creative experiences are in any way by themselves a symptom of mental illness, as it is still not clear what makes some such experiences beneficial whilst others lead to the impairment or distress of diagnosable mental pathology. However, people who have profoundly different experiences of reality or hold unusual views or opinions have traditionally held a complex role in society, with some being viewed as kooks, whilst others are lauded as prophets or visionaries.

Psychosis has been traditionally linked to the neurotransmitter dopamine. In particular, the dopamine hypothesis of psychosis has been influential and states that psychosis results from an overactivity of dopamine function in the brain, particularly in the mesolimbic pathway. The two major sources of evidence given to support this theory are that dopamine-blocking drugs (i.e. antipsychotics) tend to reduce the intensity of psychotic symptoms, and that drugs which boost dopamine activity (such as amphetamine and cocaine) can trigger psychosis in some people (see amphetamine psychosis).

Nevertheless, the connection between dopamine and psychosis is generally believed to be complex. First of all, while antipsychotic drugs immediately block dopamine receptors, they usually take a week or two to reduce the symptoms of psychosis. Moreover, newer and equally as effective antipsychotic drugs actually block slightly less dopamine in the brain than older drugs whilst also affecting serotonin function, suggesting the 'dopamine hypothesis' is vastly oversimplified.

Psychiatrist David Healy has criticised pharmaceutical companies for promoting simplified biological theories of mental illness that seem to imply the primacy of pharmaceutical treatments while ignoring social and developmental factors which are known to be important influences in the aetiology of psychosis8.

Some theories regard many psychotic symptoms to be a problem with the perception of ownership of internally generated thoughts and experiences9. For example, the experience of hearing voices may arise from internally generated speech that is mislabelled by the psychotic person as coming from an external source.

Cannabis and psychosis

There is now growing evidence for a small but significant link between cannabis use and vulnerability to psychosis11. Some studies indicate that cannabis use correlates with a slight increase in psychotic experience, which may trigger full-blown psychosis in some people. Early studies have been criticized for failing to consider other drugs (such as LSD) that the participants may also have used before or during the study, as well as other factors such as possible pre-existing mental health issues. However, more recent studies with better controls have still found a small increase in risk for psychosis in cannabis users. It is still not clear whether this is a causal link, and it may be that cannabis use only increases the chance of psychosis in people already predisposed to it. The fact that cannabis use has increased over the past few decades, whereas the rate of psychosis has not, suggests that a direct causal link is unlikely for all users.

Non-psychiatric conditions and psychosis

Psychosis can be a feature of several diseases, often when the brain or nervous system is directly affected. However, the fact that psychosis can occasionally arise in parallel with a number of ailments (including diseases such as flu or mumps for example) suggests that a variety of nervous system stressors can lead to a psychotic reaction. Psychosis arising from non-psychiatric conditions is sometimes known as 'secondary psychosis'. The mechanisms by which this happens is still not clear, but the non-specificity of psychosis has led Tsuang and colleagues to argue that "psychosis is the 'fever' of mental illness—a serious but nonspecific indicator"12.

There are some non-psychiatric conditions which are linked particularly to psychosis, which may include:

  • Brain tumour
  • Dementia with Lewy bodies
  • Hypoglycemia
  • Intoxication
  • Multiple sclerosis
  • Systemic Lupus Erythematosus (it is one of the 19 types of nervous system involvement in SLE).
  • Sarcoidosis