Illicit drug use is common among heavy cigarette smokers in the general population, but among outpatients with schizophrenia who are heavy smokers, it is most common in the first decade of illness, according to findings from a study of 70 patients and 97 controls.

The findings have important implications for the management of schizophrenia patients who are in the early stages of their disease, Kristen M. Mackowick of the National Institute on Drug Abuse and her colleagues reported in the August issue of Schizophrenia Research.

The prevalence of cigarette smoking among those with schizophrenia is 58%-90%, compared with about 20% in the general population, a particular problem given that those with mental illness or substance use disorders are more susceptible to smoking-related illnesses because they smoke more cigarettes per day and have more difficulty quitting.

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A new study shows that patients in the early stages of schizophrenia are considerably more likely to smoke.

“A significant cause for concern in the schizophrenia population, in addition to increased morbidity and mortality rates, is that cigarette smoking and use of other drugs often covary,” the investigators said, noting that one study showed that the odds of someone with a substance abuse diagnosis also having a diagnosis of schizophrenia was 4.6 times higher than for the rest of the population. Other studies show that the combination of psychiatric disorders with a substance use disorder greatly increases the likelihood that an individual will need psychological health services, be more aggressive, and be less compliant with medication.

In the current study, lifetime drug use was similar among the participants with schizophrenia and controls, except that more of those with schizophrenia reported ever using hallucinogens (49% vs. 25%) and inhalants (21% vs. 5%).

Notably, fewer than 3% of schizophrenia participants “reported current use of any drug other than alcohol (17% current use), whereas considerably higher percentages of controls reported current use of some drug (alcohol 69%, heroin 12%, cocaine 25%, marijuana 45%). However, more schizophrenia participants than controls reported past, but not current, use of some substances (alcohol 71% vs. 29%, cocaine 51% vs. 34%, marijuana, 84% vs. 49%) with most having not used for more than a year,” the investigators found (Schizophrenia Research 2012;139:194-200).

After controlling for age, they also found that most current substance use occurred between at age 20-30 years in both patients and controls, with discrepancies becoming greater with increasing age. The rates of current use declined for schizophrenia patients, but not for controls, they noted.

The findings suggest that the co-occurrence of schizophrenia, tobacco dependence, and drug use remains a serious health concern, as well as a barrier to improving health and quality of life in those with schizophrenia, they said, noting that the finding that schizophrenia participants reported more past substance use than controls is a concern, because “early-onset drug use may increase an already vulnerable individual’s chance of developing psychosis.”

Research has shown, for example, that individuals who possess the Val allele on the COMT gene and who had early-onset cannabis use were at an increased risk of developing psychotic symptoms, they noted.

The finding with respect to inhalant use also is of concern, as it has been shown to have the potential to produce persistent psychotic symptoms in those at risk for psychosis, they added.

Participants in this study were adults aged 18-65 years who smoked at least five cigarettes daily, and who had a breath carbon monoxide (CO) level of at least 8 parts per million. Patients were outpatients with a DSM-IV diagnosis of schizophrenia or schizoaffective disorder; controls had no major Axis I psychotic disorder as determined by the SCID-I (Structured Clinical Interview for DSM-IV Axis I Disorders).

The study consisted of one 2- to 3-hour session involving screening (the CO measurement and SCID), smoking of one cigarette to standardize the time since last tobacco exposure, and completion of a semistructured interview and research questionnaires.

The findings – particularly the substantial history of past substance use among schizophrenia participants aged 20-30 years – underscore the need for enhanced efforts to treat tobacco dependence in those with schizophrenia, both for the obvious health benefits and to help protect against initiation of drug use, the investigators said.

“Clinicians should also be vigilant when treating schizophrenia patients who are in the early stages of their illness, as prodromal and first-episode patients may be more vulnerable to drug use, as we observed more past drug use than current use in our schizophrenia participants,” they concluded.

This study was supported by the Intramural Research Program of the National Institutes of Health, the National Institute on Drug Abuse, and by a NIDA Residential Research Support Services contract. Ms. Mackowick had no disclosures to report. Coauthor Robert P. McMahon reported serving as a consultant to Amgen. Coauthor Deanna L. Kelly reported receiving grant support from Janssen Pharmaceuticals and Bristol-Myers Squibb.