Smoking and psychosis-Part 1
The prevalence of smoking among people with psychosis is notoriously high, and smoking is often regarded as a form of self-medication, but a new analysis suggests smoking itself may play a causative role in the development of psychotic illness, new research shows.
“[Our findings] suggest to clinicians that we should probably be more aggressive in how we manage smoking in people presenting with psychosis, in much the same way as we now consider managing cannabis use in people with psychosis,” coauthor Sameer Jauhar, MD, an honorary consultant psychiatrist at the Maudsley Hospital, King’s College London, United Kingdom, told Medscape Medical News.
The study was published online July 9 in Lancet Psychiatry.
Self-Medication Hypothesis Debunked?
The analysis included 61 studies with data through 2014 involving 14,555 tobacco smokers and 273,162 nonsmokers. The studies included international populations, and two studies were from China, where smoking rates are lower than in Europe and North America.
The investigators hypothesized that if the high rate of smoking among people with psychosis was related to self-medication, then smoking rates could be expected to be normal at the time of the first psychotic episode and subsequently increase in reaction to the symptoms.
Instead, the analysis of case-control studies found that 57% of people with a first episode of schizophrenia were already smokers, for an overall odds ratio of 3.22 (95% confidence interval [CI], 1.63 – 6.33), with some evidence of publication bias.
A subanalysis of five longitudinal, prospective studies showed a more modest association, but daily smokers were still approximately twice as likely to develop new psychotic disorders as nonsmokers (relative risk, 2.18; 95% CI, 1.23 – 3.85).
In addition, those who smoked daily were found to develop psychotic illness approximately 1 year earlier than nonsmokers.
There was no significant difference in age of starting smoking between those who did, and did not, develop psychosis.
“We think that the earlier onset of psychosis and higher risk in smokers of developing psychosis (albeit based on few studies) calls into question the self-medication hypothesis,” the authors wrote.
The findings collectively satisfy the Bradford Hill conditions, which include strength, consistency, specificity, and other factors, for evidence suggesting a causal relationship between smoking and psychosis, the authors conclude.
Although Dr Jauhar said he knew of no evidence linking smoking reduction or cessation with a reduction in psychosis, previous research by his team, published in the British Journal of Psychiatry, has shown some reduction in symptoms in those who quit.
“Our [previous study] suggested that positive psychotic symptoms were increased in those with nicotine dependence, [and] what was interesting in that article was that quitters and nonsmokers showed lesser severity of positive symptoms than those patients with nicotine dependence,” he said.
“[However,] the other issue will be that if patients’ symptoms do increase, there is a high probability that this will lead to treatment-seeking, so it may be difficult to look at.”