eng Oriental Scientific Publishing Company Biomedical and Pharmacology Journal 0974-6242 2023-06-30 16 2 1189 1199 10.13005/bpj/2699 49201 article Rawnaq A. Aladhab 1 Abdulkareem H. Abd 2 Haider A. Alidrisi 3 Majid H. Alabbood 4 Department of Pharmacology/College of Pharmacy, University of Basrah, Basrah/Iraq. Department of Pharmacology, Pharmacology and Toxicology, College of Medicine/ AL-Nahrain University/Baghdad/Iraq College of Medicine, University of Basrah, Department of medicine, endocrine division, Basrah/Iraq. Endocrinologists, Alzahraa College of Medicine, University of Basrah, Basrah/Iraq Objectives: This study aims to detect the association of the OCT1 genetic polymorphism with the efficacy and gastrointestinal side effects of metformin in newly diagnosed type 2 diabetes and drug naïve patients in Basrah/Southern Iraq. Methods: This was a prospective cohort population-based study of (102) newly diagnosed type 2 diabetics from February 2022 to December 2022. Newly diagnosed type 2 diabetes, drug naïve patients with an HbA1c range of (6.5-9.9) were included in the study. All the participants received immediate-release metformin. Metformin responders were patients whose HbA1c levels decreased by ≥1% after three months of treatment. Patients were genotyped for one of the most common SNPs in the OCT1 gene (SLC22A1): M420del (rs72552763) of axon 7, using ARMS- PCR genotyping assays. Results: Gastrointestinal side effects were observed in 15% of the patients. Out of the total of 102 participants, 69 were responders and 33 were non-responders. The homozygous genotype (AA) “reference type” of the SLC22A1 (rs72552763) gene polymorphism was significantly found in the responders' group; p-value = 0.0001. The homozygous genotypes (deletion/deletion) of the SLC22A1 (rs72552763) gene were more common among the non-responders' group; p-value = 0.0001. About 87% of those with gastrointestinal side effects carried the AA genotype. All the patients without gastrointestinal side effects carried the homozygous del/del genotype; P-value 0.005. Conclusions There was a significant association between the rs72552763 gene polymorphism and metformin efficacy and GI side effects. https://biomedpharmajournal.org/vol16no2/genetic-polymorphism-in-the-organic-cation-transporters-1-oct1-gene-and-its-effect-on-therapeutic-efficacy-and-gastrointestinal-side-effects-of-metformin-in-patients-with-type-2-diabetes-mellitus-in/ GI side effects OCT1 polymorphism Metformin Type-2 Diabetes Mellitus