Cannabis & Psychosis: Exploring the Link

Also visit:

Cannabis & Psychosis: Exploring the Link

Continued cannabis use and risk of incidence and persistence of psychotic symptoms: 10 year follow-up cohort study

The abstract of an article published in the March 1st edition of the British Medical Journal:

By Rebecca Kuepper, research psychologist (1), Jim van Os, professor (1), visiting professor (2), Roselind Lieb, professor (3,4), Hans-Ulrich Wittchen, professor (4,5), Michael Höfler, research statistician (5), Cécile Henquet, lecturer (1)

1. Department of Psychiatry and Neuropsychology, South Limburg Mental Health Research and Teaching Network, EURON, Maastricht University Medical Center, Maastricht, Netherlands
2. King’s College London, King’s Health Partners, Department of Psychosis Studies, Institute of Psychiatry, London, UK
3. Department of Psychology, Division of Epidemiology and Health Psychology, University of Basel, Switzerland
4. Max Planck Institute of Psychiatry, Munich, Germany
5. Institute of Clinical Psychology and Psychotherapy, Technical University Dresden, Germany
   

Objective

To determine whether use of cannabis in adolescence increases the risk for psychotic outcomes by affecting the incidence and persistence of subclinical expression of psychosis in the general population (that is, expression of psychosis below the level required for a clinical diagnosis).


Design

Analysis of data from a prospective population based cohort study in Germany (early developmental stages of psychopathology study).


Setting

Population based cohort study in Germany.


Participants

1923 individuals from the general population, aged 14-24 at baseline.


Main outcome measure

Incidence and persistence of subthreshold psychotic symptoms after use of cannabis in adolescence. Cannabis use and psychotic symptoms were assessed at three time points (baseline, T2 (3.5 years), T3 (8.4 years)) over a 10 year follow-up period with the Munich version of the composite international diagnostic interview (M-CIDI).


Results

In individuals who had no reported lifetime psychotic symptoms and no reported lifetime cannabis use at baseline, incident cannabis use over the period from baseline to T2 increased the risk of later incident psychotic symptoms over the period from T2 to T3 (adjusted odds ratio 1.9, 95% confidence interval 1.1 to 3.1; P=0.021). Furthermore, continued use of cannabis increased the risk of persistent psychotic symptoms over the period from T2 to T3 (2.2, 1.2 to 4.2; P=0.016). The incidence rate of psychotic symptoms over the period from baseline to T2 was 31% (152) in exposed individuals versus 20% (284) in non-exposed individuals; over the period from T2 to T3 these rates were 14% (108) and 8% (49), respectively.


Conclusion

Cannabis use is a risk factor for the development of incident psychotic symptoms. Continued cannabis use might increase the risk for psychotic disorder by impacting on the persistence of symptoms.

Posting of this abstract is for the purposes of research into psychosis.

Also see:

Cannabis use 'raises psychosis risk' - study

Cannabis use 'doubles risk of psychosis for teenagers'

Marijuana Use Linked to Risk of Psychotic Symptoms

Continued cannabis use and risk of incidence and persistence of psychotic symptoms: 10 year follow-up cohort study


Image credit

Cannabis May Influence Onset of Psychosis

An article posted on February 7th by Scientific American:

Research to be published this summer finds that the use of cannabis is associated with the early onset of psychosis.

By Christie Nicholson

Pot is one of those drugs that appears to maintain a fairly good rep, despite its growing bad rep. Consider this research that will be published this June in the Archives of General Psychiatry.

This particular study found that marijuana use is associated with early development of psychosis. Scientists analyzed 83 studies involving over 8,000 subjects who used pot and over 14,000 subjects who did not. They compared the age of onset for psychosis between these groups. And they found that those who used cannabis developed psychosis nearly three years younger than those who did not use any pot.

The researchers proposed some theories behind the pattern. One that cannabis use is a causal factor for schizophrenia, or that it precipitates psychosis in vulnerable people. They also theorize that cannabis might simply exacerbate symptoms of schizophrenia. Or the link could come from the other direction of course, those suffering from schizophrenia may be more likely to use pot.

The evidence here suggests that limiting marijuana use could delay or even prevent some cases of psychosis. And timing is important, since earlier onset of schizophrenia is linked to a worse prognosis overall.


Please click here to listen to the podcast.

Also see:

Cannabis Use and Earlier Onset of Psychosis

Evidence That Familial Liability for Psychosis Is Expressed as Differential Sensitivity to Cannabis

The abstract of a paper posted online on October 4th by the journal Archives of General Psychiatry:

An Analysis of Patient-Sibling and Sibling-Control Pairs

By Genetic Risk and Outcome in Psychosis (GROUP) Investigators

Context

Individual differences in cannabis sensitivity may be associated with genetic risk for psychotic disorder.

Objectives

To demonstrate and replicate, using 2 conceptually different genetic epidemiological designs, that (familial) liability to psychosis is associated with sensitivity to cannabis.

Design, Setting, and Participants

Sibling-control and cross-sibling comparisons using samples of patients with a psychotic disorder (n = 1120), their siblings (n = 1057), and community controls (n = 590) in the Netherlands and Flanders.

Main Outcome Measures

Positive and negative schizotypy using the Structured Interview for Schizotypy–Revised (for siblings and controls) and self-reported positive and negative psychotic experiences using the Community Assessment of Psychic Experiences (for siblings and patients). Cannabis use was assessed as current use (by urinalysis) and lifetime frequency of use (by Composite International Diagnostic Interview).

Results

In the sibling-control comparison, siblings displayed more than 15 times greater sensitivity to positive schizotypy associated with particularly current cannabis use by urinalysis (adjusted B = 0.197, P < .001) than controls (adjusted B = 0.013, P = .86) (P interaction = .04) and a similar difference in sensitivity to its effect on negative schizotypy (siblings: adjusted B = 0.120, P < .001; controls: B = –0.008, P = .87; P interaction = .03). Similarly, siblings exposed to cannabis resembled their patient relative nearly 10 times more closely in the positive psychotic dimension of the Community Assessment of Psychic Experiences (adjusted B = 0.278, P < .001) compared with nonexposed siblings (adjusted B = 0.025, P = .12) (P interaction < .001). No significant effect was apparent for the Community Assessment of Psychic Experiences negative domain, although the association was directionally similar (2 times more resemblance; P interaction = .17). Cross-sibling, cross-trait analyses suggested that the mechanism underlying these findings was moderation (familial risk increasing sensitivity to cannabis) rather than mediation (familial risk increasing use of cannabis).

Conclusions

Genetic risk for psychotic disorder may be expressed in part as sensitivity to the psychotomimetic effect of cannabis. Cannabis use may synergistically combine with preexisting psychosis liability to cause positive and negative symptoms of psychosis.

Author Affiliations:

René S. Kahn MD, PhD, Department of Psychiatry, Rudolf Magnus Institute of Neuroscience, University Medical Center Utrecht, Utrecht, the Netherlands; Don H.Linszen MD, PhD, Department of Psychiatry, Academic Medical Centre, University of Amsterdam, Amsterdam, the Netherlands; Jim van Os MD, PhD, South Limburg Mental Health Research and Teaching Network, EURON, Maastricht University Medical Centre, Maastricht, the Netherlands, and King's College London, King's Health Partners, Department of Psychosis Studies, Institute of Psychiatry, London, United Kingdom; Durk Wiersma PhD, Department of Psychiatry, University Medical Center Groningen, University of Groningen, Groningen, the Netherlands; Richard Bruggeman MD, PhD, Department of Psychiatry, University Medical Center Groningen, University of Groningen; Wiepke Cahn MD, PhD, Department of Psychiatry, Rudolf Magnus Institute of Neuroscience, University Medical Center Utrecht; Lieuwe de Haan MD, PhD, Department of Psychiatry, Academic Medical Centre, University of Amsterdam; Lydia Krabbendam PhD, South Limburg Mental Health Research and Teaching Network, EURON, Maastricht University Medical Centre; and Inez Myin-Germeys PhD, South Limburg Mental Health Research and Teaching Network, EURON, Maastricht University Medical Centre.

Posting of this abstract is for the purposes of research into psychosis and schizophrenia.

Skunk users face greater risk of psychosis, researchers warn

An article published in today's edition of The Guardian:

By Sarah Boseley, health editor

Skunk, the powerful form of cannabis dominating the street drug market, is seven times more likely to cause psychosis than ordinary cannabis, scientists say.

Dr Marta Di Forti and Prof Robin Murray, who are among the authors of today's paper published in the British Journal of Psychiatry, say skunk is now the same price as ordinary cannabis on the streets of south London, where the study was carried out, and is now the one that is easiest for young people to obtain.

The researchers at the Institute of Psychiatry in London analysed the cannabis consumption of 280 people who were admitted with a first episode of psychosis to the South London and Maudsley NHS Foundation Trust, and compared them with 174 healthy people from the area. Those who used skunk were almost seven times more likely than ordinary cannabis users to develop psychotic illnesses such as schizophrenia, they found.

"In the last five to six years it has been established that there is a link between heavy cannabis consumption and psychosis, but there is a lot of argument about how important it is," said Murray.

Most cannabis users remain healthy, he said, but he pointed to the growing takeover in the street markets of skunk, which contain 18% THC, the substance thought to trigger psychosis, compared with about 4% in cannabis resin (hash).

Forti said 80% of the cannabis sold on the streets of south-east London was now skunk. People who use skunk do not necessarily appreciate its toxicity, she said.

Those in the study had an average age of 25. Those who had psychotic attacks heard voices and had paranoid illusions, such as a conviction that neighbours or family were conspiring against them.

About 1% of the population suffer psychosis at some time in their life. Studies have shown the risk of psychosis doubles in those who use cannabis a few times.

Photograph: Floris Leeuwenberg/Corbis

Cannibis smokers have a seven-fold schizophrenia risk

Harper government devotes funds to studying the link between marijuana use and mental illness

An article published in yesterday's edition of The Toronto Star:

WINNIPEG – The Harper government is putting up $550,000 to gather research on marijuana use and mental illness.

The Schizophrenia Society of Canada will use the money to further research the links between cannabis and early psychosis as well as develop promotional materials warning youth about the dangers of smoking pot.

The money is part of Ottawa's $30 million national anti-drug strategy announced in 2007.

Chris Summerville, CEO of the Schizophrenia Society, said the public doesn't realize that cannabis users have a seven-fold increase in risk of developing schizophrenia.

He pointed to recent research out of Victoria, B.C., linking pot smoking and mental illness.

As part of the society's research, some 30 youths who have experienced psychosis will be trained to gather information about the reasons their peers use cannabis.

The results will be used to develop educational materials aimed at decreasing the use of illicit drugs among young people.

Winnipeg Conservative MP Joy Smith said Tuesday that while the public regards marijuana as a soft drug, there may be very serious consequences for young pot smokers who have a predisposition to mental illness.

"Science has shown that cannabis may actually trigger the onset of psychosis and may also intensify the symptoms for those who already have a psychotic illness," Smith said in announcing the grant.

"It has been suggested that up to 80 per cent of youth who have had a psychotic episode were using cannabis. And that's pretty shocking," said Smith, who was filling in for Health Minister Leona Aglukkaq at news conference.

Photograph by Rotbuche.