Patients with schizophrenia have elevated rates of cigarette smoking, and difficulty in smoking cessation. Cigarette smoking may reduce plasma levels of antipsychotics up to 50%.

To investigate effects of cigarette smoking in olanzapine treatment of schizophrenia.

91 patients with schizophrenia, aged 18-51, were divided into four groups. Control group (25 patients) and experimental groups: E1, 1-20 cigarettes/24h (23 patients), E2, 21-40 cigarettes/24h (22 patients) and E3, 40+ cigarettes/24h (21 patients). Patients were observed for one year period. Patients were assessed by Positive and Negative Symptom Schedule Scale (PANSS) at baseline and after one year.

No significant differences were found for PANSS score at baseline (p = 0.535). PANSS reduction at study endpoint was significant in all groups (p < 0.001). PANSS reduction was highest in non-smokers group 65.5%, and lowest in group of heavy smokers (40+ cigarettes/24h) 39.2%. There is a statistically significant difference in PANSS reduction between nonsmokers group and all smokers groups (p < 0.001). There is a statistically significant difference in PANSS reduction between E1 and E2, and E1 and E3 group (p < 0.001), and no difference between E2 and E3 group (p = 0.414). There is a statistically significant difference in olanzapine average daily dose after one year between non-smokers group and all smokers groups (p < 0.001).

Olanzapine therapy is most efficient in non-smokers group. Smoking more than 20 cigarettes per day significantly reduces effects of olanzapine therapy. Average daily dose of olanzapine is significantly lower in non-smokers group than in all three groups of smokers.