Caffeine intake among patients with schizophrenia
Caffeine intake among patients with schizophrenia |
Effects of caffeine on dopamine systems | Effects of caffeine on positive and negative symptoms | Interaction of coffee and tea with antipsychotics | Summary | Acknowledgments | References
About 85 percent of the U.S. population uses caffeine daily. The most common sources are brewed coffee (100 mg of caffeine per 6-ounce serving), instant coffee (65 mg), tea (40 mg), soda (35 mg), and chocolate (5 mg) (1). The mean caffeine intake is near 210 mg a day for the whole population, and 6 percent are heavy users—more than 500 mg a day (1).
Several reasons exist for hypothesizing that persons with schizophrenia would have high caffeine intakes. For example, patients may use caffeine to combat apathy or boredom or to offset the sedating effects of antipsychotic medications. Many persons with schizophrenia have polydipsia, and caffeine intake might increase as a result. Similarly, many psychiatric medications produce dry mouth, which might increase intake. In addition, as reviewed below, caffeine might improve negative symptoms of schizophrenia or extrapyramidal symptoms from neuroleptics. Patients taking neuroleptics may have reduced anxiety, allowing them to imbibe more caffeine.
A final possibility is that approximately 80 percent of persons with schizophrenia smoke, and many of them smoke heavily (2). Smoking increases the elimination of caffeine. Thus persons with schizophrenia may use more caffeine to make up for increased elimination of caffeine due to heavy smoking (3).
Several authors have anecdotally noted high caffeine intake among patients with schizophrenia (4), including cases of eating raw coffee (5). For example, in one study the 15 lowest users averaged 4.6 cups of coffee a day (4). Two empirical surveys of caffeine use by persons with schizophrenia were published more than 20 years ago, in 1975 and 1976. In a German study of inpatients, 71 percent used more than 500 mg of caffeine a day (6). However, in a Canadian study of both inpatients and outpatients, only 17 percent used more than 500 mg a day (7), and this consumption was not different from the 11 percent in the general population who did so.
The discrepant figures across these two studies are probably not due to cultural differences, because coffee intake in Canada and Germany was similar in 1976 (8). It is more likely that the high prevalence rate in the German study was due to institutionalization, which appears to increase caffeine use (9), or because the German study included more severely ill patients. We could find only one more recent survey of caffeine use among persons with schizophrenia. The mean caffeine intake of 26 patients was 503 mg a day, and 38 percent reported using more than 555 mg a day (10).
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Effects of caffeine on positive and negative symptoms
Caffeine intake among patients with schizophrenia |
Effects of caffeine on dopamine systems | Effects of caffeine on positive and negative symptoms | Interaction of coffee and tea with antipsychotics | Summary | Acknowledgments | References
Several case reports have described delusions and hallucinations after large intakes of caffeine by persons with (4,14) and without (15) schizophrenia. One study of 78 patients with schizophrenia found that caffeine intake was correlated with the total score on the Brief Psychiatric Rating Scale (BPRS) and with the score on a scale measuring positive symptoms, but not with scales measuring negative symptoms or extrapyramidal symptoms (16). Unfortunately, the magnitude of the effect on the BPRS score was not reported. However, when symptoms of schizophrenia and caffeine intake were followed over time in a small sample of 14 patients, only a slight correlation between caffeine intake and severity of psychosis was found (17).
Three studies have compared the symptoms of inpatients using caffeinated coffee or decaffeinated coffee (10,18,19). One study used a caffeinated-decaffeinated-caffeinated design in which inpatients alternated use for three-week periods. Scores on the anxiety and hostility subscales of the BPRS (self-reported) and irritability scores on the Nurses Observation Scale for Inpatient Evaluation (NOSIE) (nurse rated) were higher during the caffeinated-coffee periods (18), indicating a greater level of symptoms. Actual scores were not reported; thus the clinical significance of these changes is unknown.
A second study used a caffeinated-decaffeinated-caffeinated-decafeinated design with four to seven weeks in each period (19). These results were confounded by a trend for all scores to improve over time. Nevertheless, scores on subscales for hostility, hallucinations, and unusual thought content on the BPRS and irritability and psychoses scores on the NOSIE showed the expected high-low-high-low pattern. Traditional statistical tests failed to find significant differences; however, statistical tests that test specifically for the high-low-high-low pattern expected may very well have shown statistical significance. On the other hand, the changes that did occur were small and may not have been clinically significant.
A third study used a decaffeinated-decaffeinated-caffeinated-caffeinated-decaffeinated-decaffeinated design with one week in each period (10). Inpatient scores for anxiety and depression and total scores on the BPRS and NOSIE did not change across periods.
In only one study has caffeine been experimentally administered to patients (20). Caffeine, 10 mg per kg of bodyweight, was administered intravenously to persons with schizophrenia who had been caffeine free for six weeks. Caffeine increased the BPRS total score and the score on the unusual thoughts subscale as well as global nurse ratings of psychosis. These results are similar to those of the previous studies. The change in the BPRS total score was large (a 33 percent increase) and occurred for ten of the 13 subjects. In addition, caffeine improved negative symptoms; that is, it improved mood and decreased withdrawal. Interestingly, this large dose did not increase anxiety scores among these patients.
Although these results are the most direct evidence that caffeine can worsen positive symptoms (and might even improve negative symptoms), their generalizability may be limited because this study used a very large dose of caffeine—the equivalent of drinking seven cups of brewed coffee at once. Also, caffeine was administered intravenously, and the subjects had presumably lost any tolerance to caffeine (1). In addition, this study did not have a control group of persons without schizophrenia; thus the specificity of the findings is debatable. This lack of specificity is important because high doses of intravenous caffeine can cause psychotic symptoms among individuals without a history of psychosis (21).
Caffeine use and caffeine cessation produce other effects that, although not specifically relevant to schizophrenia, could influence the cause and presentation of the illness or be confused with medication side effects. Caffeine use can cause restlessness, nervousness, insomnia, rambling speech, and agitation. Whether chronic heavy caffeine users develop enough tolerance that these symptoms are of little concern is debatable (1). In addition, cessation of caffeine causes fatigue and drowsiness (1), which could be confused with prodromal or postdromal symptoms or medication side effects.
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