Objective: Antipsychotic induced weight gain is a major problem for second generation antipsychotics which may lead to diabetes and metabolic syndrome. Recent studies were mentioning that genetic factors might be relevant in antipsychotic induced weight gain. Aim of this study is evaluation of the association between IRS-1 Glyp972Arg polymorphism and olanzapine induced weight gain.

Methods: Total of 95 patients whom were diagnosed as schizophrenia by DSM-IV criteria were included to study. Body weight, body mass index and blood glucose levels of all patients were checked at the beginning and six weeks after olanzapine treatment. Blood for DNA analysis were obtained from patients and analyzed as mentioned in literature. Data were evaluated with descriptive methods and Mann Whitney U test was used for comparison of two groups.

Results: Eighty and four of patients had Glycine/Glycine and 11 patients had Glycine/Arginine genotype of IRS-1 Gly972Arg polymorphism. Despite the patients with Glycine/Glycine polymorphism gained more weight than patients with Glycine/Arginine polymorphism, the difference between Glycine/Glycine and Glycine/Arginine groups for weight change and body mass index change wasn’t statistically significant.

Conclusion: Our results showed no statistical relationship between the IRS-1 Gly972Arg polymorphism and olanzapine induced weight gain. However exploration of the other IRS genotypes and the antipsychotic-induced body weight change may help in the understanding of the mechanisms of antipsychotic-induced body weight gain.