Caffeine Intake and Levels in Smokers With Schizophrenia and Bipolar Disorder


Smoking and drinking (caffeine): Researchers analyzed caffeine intake and levels in smokers with schizophrenia and bipolar disorder.




Ms P is a 52-year-old Caucasian female with bipolar I disorder, with her most recent episode involving depression with psychotic features. Her mood disorder has been stable on ziprasidone, with no psychiatric hospitalizations in the past 5 years. She has smoked 2+ packs of cigarettes per day over 30 years. Ms P also drinks a large quantity of caffeine daily: She routinely brings a 44-ounce cup of soda with her to clinic visits and states that she drinks at least 2 of these cups daily.

She also has comorbid hypertension and chronic obstructive pulmonary disease, for which she is adherent with medication. At a recent outpatient appointment, Ms P noted that her mood was euthymic, and there was no evidence of psychosis. She reported sleeping 6 to 7 hours per night and denied significant anxiety. Ms P’s psychiatrist regularly provides psychoeducation on reducing her caffeine intake.

Almost 90% of US adults use caffeine daily, consuming an average of 186 mg per day.1 Caffeine use is higher in smokers2 and in adults with serious mental illness.3 Caffeine improves cognition through increased alertness, attention, and vigilance, via inhibition of adenosine receptors. Potential explanations for increased caffeine intake in patients with serious mental illness include:

  • Cigarette smoking, which is highly prevalent in this patient population, increases the metabolism of caffeine.
  • Caffeine may increase the urge to smoke and/or the palatability of cigarettes.4
  • Patients may self-medicate with caffeine for psychiatric symptoms, potentially due to decreased adenosinergic activity,5 or compensating for sedative effects of medications.

Despite the potential beneficial effects of caffeine, it may be harmful at higher doses.

The Current Study

Rosen and colleagues6 investigated rates of caffeine intake and blood caffeine levels in adult smokers with schizophrenia, adult smokers with bipolar disorder, and controls. The authors performed a secondary analysis of a larger study of nicotine intake and smoking behavior.7 Participants were adults aged 18 years or older who smoked 10 or more cigarettes per day and had a baseline expired carbon monoxide level >8 ppm. Participants receiving nicotine replacement, clonidine, bupropion, or nortriptyline were excluded. Pregnancy, alcohol or other substance use disorder, and use of non-cigarette tobacco products were also exclusionary.

At baseline, participants had a blood sample for caffeine and nicotine and its metabolites. They provided information about their smoking history and completed the Caffeine Consumption Questionnaire. Symptoms were assessed with the Positive and Negative Syndrome Scale and the Montgomery-Asberg Depression Rating Scale. Multivariate gamma regression with a log link were used to identify predictors of blood caffeine levels and dietary caffeine intake.

The authors analyzed data on 80 participants with schizophrenia, 80 participants with bipolar disorder, and 88 controls. The mean participant age was 41 years, 58% were male, and 56% were Caucasian. Participants smoked an average of 21 cigarettes/day. Participants with bipolar disorder had the highest self-reported median daily caffeine intake (195 mg/day), followed by schizophrenia (155 mg) and controls (132 mg). There was a significant between-group difference for median blood caffeine levels in participants with bipolar disorder (1725 ng/mL) and schizophrenia (1194 mg/mL) compared to controls (613 ng/mL).

In all 3 groups, 18% to 25% of participants consumed high daily doses of >400 mg caffeine/day. There was a small but significant correlation between self-reported caffeine intake and blood caffeine levels (r=0.17). In regression analyses, age, race (Black), and diagnosis (schizophrenia or bipolar disorder) were significant predictors of blood caffeine levels. Age and diagnosis (bipolar disorder) were significant predictors of self-reported caffeine intake.

Study Conclusions

The authors concluded that smokers with schizophrenia or bipolar disorder have higher blood caffeine levels than controls with similar smoking habits. The primary sources of caffeine in participants were coffee and soda. Given findings in the bipolar disorder group, increased caffeine was not solely attributable to effects of antipsychotic medications. Study strengths included standardized timing of assessments and blood draws, and the inclusion of controls who smoked the same amount as the patient groups. Potential limitations included potential confounding by metabolic or genetic factors, and an inability to investigate effects of sleep and oral contraceptives on caffeine levels.

The Bottom Line

Caffeine intake is high in some patients with serious mental illness. An increased understanding of the effects of caffeine on cognition, psychopathology, and overall health is needed.

Dr Miller is a professor in the Department of Psychiatry and Health Behavior at Augusta University in Augusta, Georgia. He is on the Editorial Board and serves as the schizophrenia section chief for Psychiatric TimesTM. The author reports that he receives research support from Augusta University, the National Institute of Mental Health, and the Stanley Medical Research Institute.


1. Fulgoni VL 3rd, Keast DR, Lieberman HR. Trends in intake and sources of caffeine in the diets of US adults: 2001-2010Am J Clin Nutr. 2015;101(5):1081-1087.

2. Swanson JA, Lee JW, Hopp JW. Caffeine and nicotine: a review of their joint use and possible interactive effects in tobacco withdrawalAddict Behav. 1994;19(3):229-256.

3. Gandhi KK, Williams JM, Menza M, et al. Higher serum caffeine in smokers with schizophrenia compared to smoking controlsDrug Alcohol Depend. 2010;110(1-2):151-155.

4. Treloar HR, Piasecki TM, McCarthy DE, Baker TB. Relations among caffeine consumption, smoking, smoking urge, and subjective smoking reinforcement in daily lifeJ Caffeine Res. 2014;4(3):93-99.

5. Lara DR, Dall'Igna OP, Ghisolfi ES, Brunstein MG. Involvement of adenosine in the neurobiology of schizophrenia and its therapeutic implicationsProg Neuropsychopharmacol Biol Psychiatry. 2006;30(4):617-629.

6. Rosen RL, Ramasubramani RS, Benowitz NL, et al. Caffeine levels and dietary intake in smokers with schizophrenia and bipolar disorderPsychiatry Res. 2023;319:114989.

7. Williams JM, Gandhi KK, Lu SE, et al. Nicotine intake and smoking topography in smokers with bipolar disorderBipolar Disord. 2012;14(6):618-627.

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