Increased nicotine and cotinine levels in smokers with schizophrenia and schizoaffective disorder is not a metabolic effect

It has been hypothesized that smokers with schizophrenia take in more nicotine per cigarette than smokers without this disorder. This study examines this phenomenon by comparing the serum nicotine and cotinine levels in smokers with either schizophrenia or schizoaffective disorder compared to control smokers without mental illness. Serum cotinine and nicotine levels of smokers with schizophrenia or schizoaffective disorder were 1.3 times higher than control smokers (cotinine 291 versus 227 ng/mL; p = 0.0115; nicotine 28 versus 21 ng/mL; p < 0.001) despite smoking a similar number of cigarettes per day. Similar serum 3′-hydroxycotinine (3HC) to cotinine ratios in both groups indicate that this difference was not due to differences in the rate of metabolism of nicotine or cotinine. By examining serum nicotine and 3HC / cotinine ratios in addition to cotinine, this study expands upon previous research that relied on cotinine as an indirect indicator for nicotine intake. Our data support the hypothesis that the increased serum nicotine and cotinine levels observed are attributable to an increased nicotine intake per cigarette in smokers with schizophrenia as compared to those without mental illness.