Noradrenaline and adrenaline are neurotransmitters of the sympathetic nervous system that interact with various adrenergic receptor (ADR) subtypes, and this regulates the basal metabolic rate, thermogenesis and efficiency of energy utilization. We examined a possible role of the gene coding for ADRA1A receptor in weight gain in schizophrenia subjects exposed to antipsychotics. A total of 401 schizophrenia in-patients treated with antipsychotics for >2 years were recruited and a final 394 DNA samples were genotyped. Their body mass indexes (BMIs) were recorded for 12 months and parameterized to be correlated in regression. Among the 58 single-nucleotide polymorphisms (SNPs) genotyped, 44 valid SNPs, which had minor allele frequency > or =0.03, were analyzed in statistics. Linear regression model with age, gender, diabetes, use of typical antipsychotics and use of atypical antipsychotics as covariates, with or without gender interaction, showed evidence of associations between the ADRA1A gene and BMI. Most of the SNPs associated with BMI are located in the promoter and intron regions, and being female appeared to enhance the gene effect. Our study suggests that the ADRA1A gene is involved in weight gain among schizophrenia patients treated with antipsychotics. Further molecular dissection of the ADRA1A gene warrants better understanding on weight gain mechanisms in schizophrenia.