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Introduction Prevalence of tobacco use in patients with psychotic disorders (PD) is 40–70%. It has been described use of tobacco induces Cytochrome P450 activity, increasing some antipsychotic drugs metabolism, thus reduces their plasma levels. Aim We carried out the present study to analyze the association between tobacco use and doses of antipsychotics in patients with PD and to determine whether patients suffering from PD who smoke may require antipsychotic dose adjustments. Methods We designed a cross-sectional study of patients between 18 and 55 years, with a PD, treated with the same antipsychotic and dose for the last 6 months: – consumption of cigarettes per day was determined; – the doses of the used antipsychotic drugs were converted into chlorpromazine equivalents; – statistical analysis was performed with STATA. Results The sample consisted of 30 women (29.7%) and 71 men (70.3%). Mean age was 43.7 years old (SD: 8.0). Sixty-three patients were smokers (63.6%), being the other 36 non-smokers (36.4%). Mean dose of chlorpromazine in smokers was 1088.04 mg/day (SD: 697.17 mg/day) whether in non-smokers was 699.16 mg/day (SD: 556.07 mg/day). Mean differences of antipsychotic dose were statistically significant between the two groups of smokers and non-smokers ( P = 0.005). We also found significant association between consumption of cigarettes and antipsychotics doses ( P = 0.0001), so that, per each cigarette/day, dose of Chlorpromazine increased 19.81 mg/day. Conclusion Patients suffering from PD smoke required higher doses of antipsychotics. These results suggest that patients who smoke might need higher doses of antipsychotic and that, if consumption of tobacco varies, antipsychotics doses might need to be adjusted. [ABSTRACT FROM AUTHOR]