Attention-Deficit/Hyperactivity Disorder (ADHD) is a highly common neurodevelopmental disorder marked by inattention, hyperactivity, and impulsivity. ADHD is often under/misdiagnosed. Current diagnosis relies on clinical interviews and behavioral assessments, which do not include objective biomarkers. Saliva is a noninvasive fluid that can reflect underlying physiological and molecular processes, and it has shown potential in research on ADHD. Studies have examined various salivary biomarkers, including alpha-amylase, immunoglobulins, cortisol, trace metals such as copper, zinc, and manganese, and DNA methylation patterns. Eight out of the Nine studies included showed a difference in various biomarker levels in ADHD in comparison to controls. Results are mixed, with some markers elevated, some reduced, and others showing no clear differences from controls. This variability highlights that research in this area is still exploratory. Future studies should focus on combining multiple salivary markers into integrated profiles, which may improve diagnostic accuracy and provide a better understanding of the biological processes involved in ADHD.