Since its connection between the brain and the gut (the brain‐gut axis), as well as the growing clinical evidence indicating the efficacy of SSRIs (Selective serotonin reuptake inhibitors) in treating these neurological disorders/conditions, it has been demonstrated that serotonin and its receptors, specifically the SERT and its polymorphisms, play a potential role in the pathophysiology of functional digestive disorders such as irritable bowel syndrome (IBS) (Margolis, 2017; Wang et al., 2004; Yaghoubfar et al., 2020). The gene discussed is SLC6A4; the disease is irritable bowel syndrome.