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Dr Brian Boettcher Consultant Psychiatrist Shelton Hospital, Shropshire’s Community & Mental Health Services NHS Trust, Bicton Heath, Shrewsbury, SY3 8DN


The drug induced psychosis seen when Cannabis is the main substance being abused is distinct phenomenologically from other psychosis.

It is unusual for such a psychosis to occur without other drugs being involved to some extent and so it is difficult to tease out the differences between the effects of Cannabis and other drugs.

However it is misleading and dangerous, to our youth in particular, to label Cannabis as “soft”. In fact the serious adverse effects of Cannabis have been known for some time now and Hall and Solowij in the British Journal of Psychiatry sounded warnings in 1997 about such issues as dependence on Cannabis, adolescent developmental problems, permanent cognitive impairment as well as involvement in and the development of psychosis.[1]

There are suggestions that in a small number of cases Cannabis is capable of precipitating psychosis, going on to the chronic picture described below, in people who have had no family and personal history of psychiatric illness.There have been suggestions that such people may be the ones who have started Cannabis in their teens and caused disturbance to neural connectivity. However, it seems Cannabis can precipitate or exacerbate a schizophrenic tendency in a characteristic manner.[2]


International Classification of Diseases (ICD-10)

Often the combination of symptoms makes one suspicious that schizophrenia is present but at the same time there is an affective component. There may be the suspicion that the condition, either in part of whole, is feigned for reasons that are unclear because the pattern of symptoms do not fall easily into the usual criteria for psychosis. Drug taking is often denied, or the amount that is admitted by the patient is so little that one cannot say that this accounts for the current symptoms. Worse still, patients may not even consider Cannabis as an illicit or dangerous drug and so do not mention using it. Hallucinations are vague and delusions may be transitory with little in the way of thought disorder. There is often a lack of volition and a history of gradually deteriorating social ability and contact with others, including significant others. This history will often be verified by relatives and close friends who may be either completely ignorant of the drug taking, or confirm that there has been some in the past but believe that there has been little drug taking recently. There is often a depressive component with suicide attempts in the past but nothing recent or, if there is, then they are only ineffectual pleas for help. The person has usually lost his or her job some months or weeks before due to their poor performance at work. There is often very poor memory and concentration, which may be marked at the time of presentation. Paranoid delusions may be present and quite severe which can be the most alarming psychotic feature and result in hospital admission. If confronted with aggressive and authoritarian staff, who indicate verbally or non-verbally, that they do not believe the patient, the patient may become violent or simply leave against medical advice. There is a slow and gradual effect of cannabis and the symptoms continue to worsen for some time after the person stops using it. Thus by the time of presentation the person may be so disorganised and confused that they can’t even arrange their next “cone” or “joint”. Over the following few days the symptoms ease quickly. The improvement is easily credited to the neuroleptics and/or the antidepressants, which may in fact have contributed to the improvement. Symptoms such as the paranoia, hallucinations and depression fade until the patient is allowed to go on leave from the hospital and, a worsening of the symptoms may follow this. More often than not the nursing staff are the first to become suspicious that drugs have been taken when the patient is on leave from the hospital.

It could even be that the drug screen only indicated small dose drug taking or even absent. The International Classification of Disease indicates the following symptoms due to Cannabis.

“There must be dysfunctional behaviour, as evidenced by at least one at of the following:


(1) Apathy and sedation

(2) Disinhibition

(3) Psychomotor retardation

(4) Impaired attention

(5) Impaired judgement

(6) Interference with personal functioning.

C. At least one of the following signs must be present:

(1) Drowsiness

(2) Slurred speech

(3) Pupillary constriction (except in anoxia from severe overdose, when pupillary dilatation occurs)

(4) Decreased level of consciousness (e.g. Stupor, coma)

F12.0 Acute intoxication due to use of cannabinoids F12.0 DCR-10

A. The general criteria for acute intoxication (F1x.0) must be met.

B. There must be dysfunctional behaviour or perceptual disturbances including at least one at least one of the following:


(1) Euphoria and disinhibition

(2) Anxiety or agitation

(3) Suspiciousness or paranoid ideation

(4) Temporal slowing (a sense that time is passing very slowly, and/or the person is experiencing a rapid flow of ideas)

(5) Impaired judgement

(6) Impaired attention

(7) Impaired reaction time

(8) Auditory, visual or tactile illusions

(9) Hallucinations, with preserved orientation

(l0) depersonalization

(11) derealization

(12) Interference with personal functioning


[3] DSM IV also has similar but less complete information under the heading of Cannabis Induced Psychotic Disorder and refers the reader to a general description of “ Sunstance­Induced Psychotic Disorder”. That is the difference in the phenomenology of Cannabis Psychosis and other substance induced psychosis is not made, however this is now rather dated being 1994 when published.[4]

It can be seen from this that the range of symptoms is quite extensive and not confined to the core symptoms mentioned at the beginning.


Patients are left with the well-recognised and permanent symptoms of memory loss, apathy, loss of motivation and, paranoid ideation. These symptoms known as “ the Amotivational Syndrome” in the past are usually permanent.[5] If Cannabis using resumes then the acute symptoms redevelop. The chronic state can also be arrived at without a preceding psychotic episode. After Cannabis started to be widely used about 20 years ago, for permanent damage to occur it was felt by some that Cannabis had to be heavily used over at least three years [6]. However, there is accumulating evidence that smaller amount will do damage also and in animals “ deficits on tasks dependent on frontal lobe function have been reported in cannabis users” [7]. It is very difficult to conduct research in this area, as it is not acceptable to harm humans by doing trials with damaging substances such as Cannabis. However there is accumulating evidence of the psychological consequences of using Cannabis [8]. It is logical that to get the permanent “ Amotivational Syndrome” small amounts to damage have to accumulate incrementally. All this is in addition to the recognised danger of a recurrence of a pre-existing illness, such as Schizophrenia or Manic-depressive disorder. There are suggestions that Cannabis “ caused schizophrenia in young people and (or) enhanced the symptoms, especially in young people poorly able to cope with stress or in whom the antipsychotic therapy was unsuccessful”. [9] Caspari found “patients with previous cannabis abuse had significantly more rehospitalizations, tended to worse psychosocial functioning, and scored significantly higher on the psychopathological syndromes "thought disturbance" (BPRS) and "hostility" (AMDP). These results confirm the major impact of cannabis abuse on the long-term outcome of schizophrenic patients”.[10]P



[1] Hall W, Solowij N, “ Long-term Cannabis use and Mental Health “ 1997 British Journal of Psychiatry, August, 171:107-8

[2] Hall A, Degenhardt, “Cannabis and Psychosis” Australian National Drug and Alcohol Research Centre, Presented at The Inaugural International Cannabis and Psychosis Conference 1999 , Melbourne 16-17 February 1999

[3] World Health Organisation, Geneva, (1992) “ The ICD-10 Classification of Mental and Behavioural Disorders”

[4] Diagnostic and Statistical Manual of Mental Disorders , Fourth Edition, American Psychiatric Association,1994

[5] Schwartz RH “Marijuana: an overview”. Pediatr Clin North Am 1987 Apr;34(2):305-17 .

[6] Boettcher B, Medical Journal of Australia 11/25 December 1982 “Marijuana and Apathy”

[7] Jentsch J D, Verrico C D, Le D, Roth RH, “ Repeated exposure to dleta9-tetragydrocannabinol reduces prefrontal cortal dopamine metabolism in the rat “ ,Neurosci Lett (1998) May 1;246(3):169-72

[8] Hall W, Solowji N, Lemon J, The health and psychological consequences of Cannabis use. National Drug Strategy Monograph Series no 25. Canberra: Australia Government Publishing Service, 1994

[9] van Amsterdam JG, van der Laan JW, Slangen JL, “Cognitive and psychotic effects after cessation of chronic cannabis use “ Ned Tijdschr Geneeskd 1998 Mar 7;142(10):504-8

[10] Caspari D, “Cannabis and Schizophrenia: Results of a follow-up Study” Eur Arch Psychiatry Clin Neurosci 1999;249(1):45-9


Dr Brian Boettcher Consultant Psychiatrist Shelton Hospital, Shropshire’s Community & Mental Health Services NHS Trust, Bicton Heath, Shrewsbury, SY3 8DN


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