It has been reported that C825T variant in the gene encoding the G-protein subunit β3 (GNB3) is associated with antipsychotic-induced weight gain and obesity. We investigated the association of the GNB3 and antipsychotic-induced weight gain as well as body mass index (BMI) using meta-analytical techniques. Our analysis of 402 schizophrenia subjects showed a trend (p = 0.072) only under a fixed-model. As it was observed heterogeneity among the studies (p = 0.007), we re-analyzed using a random-effects framework and no significance was found (p = 0.339). No evidence for bias publication was reported (p = 0.868). Our analysis of 18,903 subjects showed a trend (p = 0.053) associating CC and lower BMI under a fixed model. Although no significant association was found, the same pattern (CC and lower antipsychotic-induced weight gain) was observed. Our meta-analysis indicates that firmly establishing the role of pharmacogenetics in clinical psychiatry requires much larger sample sizes that have been reported.