Experts at the Institute of Psychiatry in London are publishing research suggesting that smoking cigarettes may be a contributory cause of schizophrenia (a psychotic disorder). This startling finding includes a just published study, plus research to be published in the near future, all of which appears to suggest an association between smoking cigarettes and developing psychosis.
These new findings raise a question - could the most obvious fact about cannabis - that it is usually consumed in combination with tobacco - have been neglected in researching the link between cannabis and psychosis?
In the new study just published, 'Cigarette smoking and cannabis use are equally strongly associated with psychotic-like experiences: a cross-sectional study in 1929 young adults', smoking tobacco was found to be an equally strong predictor of frequency of psychotic experiences as monthly cannabis use.
This latest investigation from researchers at University Medical Centre Utrecht, The Netherlands, and the Institute of Psychiatry, London, was partly inspired by the well-known observation that majority (as much as 70-85%) of patients with schizophrenia smoke cigarettes.
Within academic medicine the association between cannabis use and psychotic symptoms is ﬁrmly established.
Some have argued those who begin to experience psychosis initiate using cannabis in attempts to 'self-medicate' distress, but this suggestion has been rebuffed by a host of surveys, according to Sir Robin Murray - Professor of Psychiatry at the Institute of Psychiatry in London. Sir Robin Murray is involved in forthcoming research which will further strengthen the evidence smoking cigarettes may well be a contributory cause of schizophrenia.
Cannabis contains many chemicals, some of which may have psychosis-inducing effects, while one may even have anti-psychotic properties. Research is currently underway in various pharmaceutical laboratories isolating the active anti-psychotic ingredients in order to deploy them in treatments for psychosis.
The authors of this new study van Gastel, MacCabe, Schubart, Vreeker, Tempelaar, Kahn and Boks point out that previous research has found nicotine dependency is associated with psychotic symptoms. The more you smoked when young the more likely you are to develop psychotic symptoms later in life. Other research has independently established an association between cigarette smoking and psychosis.
The authors of this new study, just published in the journal Psychological Medicine, conclude it might be that individuals who are already prone to Psychotic Experiences are also more inclined to smoke cigarettes and use cannabis. They caution that heavy use of cannabis leads to additionally increased psychosis proneness. The study found that moving from monthly use of cannabis to weekly, was associated with a stronger link between cannabis and Psychotic Experiences.
To explain this startling finding, that in a large sample of young adults aged 18 to 30 years, cigarette smoking was as strongly associated as cannabis use with frequency of Psychotic Experiences, might involve a new understanding of how tobacco effects the brain.
The authors suggest that smoking profoundly effects the nervous system - which is why it's pleasurable. The chemical nerve transmitters cigarette smoking increases the levels of, including the neurotransmitter dopamine, are not just linked with feelings of reward but also psychosis. A more remote possibility, the authors suggest, is that Psychotic Experiences could be the result of nicotine withdrawal.
This most recent research was partly inspired by a study entitled 'A prospective study of smoking in young women and risk of later psychiatric hospitalization', published in the Nordic Journal of Psychiatry.
Researchers in Copenhagen followed 7,926 young women from 1959 to 2007, and found significant positive associations between number of cigarettes smoked and schizophrenia-like disorders, substance abuse and other non-psychotic disorders. A total of 1,301 of these women were admitted to a hospital for psychiatric reasons, and a strong positive association between number of cigarettes smoked and being admitted for a psychiatric disorder was found.
The authors of the study, Holger Sørensen, Erik Mortensen, June Reinisch and Sarnoff Mednick conclude that as the relationships between amount of cigarettes smoked in 1959 - 61, and increased risk of psychiatric hospitalization later in life, were similar for almost all the major categories of mental illness, it's possible there is a non-specific association between smoking and mental illness.
But smoking might be even more dangerous for your mental than that, as a study published in the American Journal of Psychiatry, entitled 'Higher Rates of Cigarette Smoking in Male Adolescents Before the Onset of Schizophrenia: A Historical-Prospective Cohort Study' suggests.
This study used the fact that each year, a random sample of male Israeli military recruits, who have been screened and found not to be suffering from major mental illness, complete a smoking questionnaire. Through the Israeli National Psychiatric Hospitalization Case Registry, 14,248 of these adolescents were followed to determine later psychiatric hospitalization.
Compared to non-smokers, adolescents who smoked 10 cigarettes/day or more were over twice as likely to be hospitalized later for schizophrenia.
The authors go on to argue that if smoking tobacco is in some way causing schizophrenia, then the reduction in incidence of schizophrenia that would be observed if no one smoked, would be very high, probably 23%.
It's possible that you need a combination of the 'wrong' genes plus the risk activity (like smoking cannabis or tobacco) in order to generate psychotic illness.
But smoking tobacco or cannabis heavily, remains an activity most doctors would warn against as bad for your physical and mental health.
If smoking cigarettes is established as a significant risk factor for future psychosis, then should cigarette packet warnings include the new threats now uncovered to your mental health? If we are not going to be legally tougher on tobacco, in order to retain consistency, does this new research mean the law should now become more liberal on cannabis?