Attention deficit hyperactivity disorder (ADHD) is a neurodevelopmental condition marked by hyperactivity, impulsivity, and inattentiveness that are disproportionate to the patient's developmental stage. Individuals with ADHD often experience gastrointestinal (GI) issues, indicating a potential link with the gut microbiome. This study aims to explore how various parameters influence the production and consumption of metabolites in the brain by developing an integrated gut-brain metabolic model, examining the impact of gut microbiota-derived metabolites on the human brain. Genome-scale metabolic models (GEMs), which consider gene-protein-reaction relationships, are utilized to simulate metabolic processes in gut microorganisms. A comprehensive genome-scale metabolic model of the human brain, comprising 812 metabolites, 994 reactions, 671 genes, and 71 metabolic pathways, serves as the healthy brain reference. To mimic an ADHD brain, the gene NOS1 is removed from the healthy model. An integrated gut-brain model is created using a three-compartment approach (gut, blood, and brain). This modeling technique, which accounts for microbial genome-environment interactions and their metabolite interactions with other human organs, helps identify the GI mechanisms underlying ADHD toward enhancing the quality of life for affected individuals. Moreover, understanding the relationship between ADHD, age, gender, and diet can help in developing more effective, personalized approaches to managing ADHD.