Domperidone is a useful alternative to metoclopramide for treatment of gastroparesis due to better tolerability. Effectiveness and side-effects from domperidone may be influenced by patient-related factors including polymorphisms in genes encoding drug-metabolizing enzymes, drug transporters, and domperidone targets.The aim of this study was to determine if demographic and pharmacogenetic parameters of patients receiving domperidone are associated with response to treatment or side-effects.Patients treated with domperidone for gastroparesis provided saliva samples from which DNA was extracted. Fourteen single-nucleotide polymorphisms (SNPs) in seven candidate genes (ABCB1, CYP2D6, DRD2, KCNE1, KCNE2, KCNH2, KCNQ1) were used for genotyping. SNP microarrays were used to assess single-nucleotide polymorphisms in the ADRA1A, ADRA1B, and ADRA1D loci.Forty-eight patients treated with domperidone participated in the study. DNA was successfully obtained from each patient. Age was associated with effectiveness of domperidone (p=0.0088). Genetic polymorphism in KCNH2 was associated with effectiveness of domperidone (p=0.041). The efficacious dose was associated with polymorphism in ABCB1 gene (p=0.0277). The side-effects of domperidone were significantly associated with the SNPs in the promoter region of ADRA1D gene.Genetic characteristics associated with response to domperidone therapy included polymorphisms in the drug transporter gene ABCB1, the potassium channel KCNH2 gene, and α1D--adrenoceptor ADRA1D gene. Age was associated with a beneficial response to domperidone. If verified in a larger population, this information might be used to help determine which patients with gastroparesis might respond to domperidone and avoid treatment in those who might develop side-effects.