Insomnia, a prevalent sleep disorder, significantly impacts both physical and mental health. This literature review aims to explore the effects of insomnia on various health outcomes and to identify adult risk factors associated with the condition. The review is based on an extensive search of electronic databases, including PubMed, Scopus, PsycINFO, and Google Scholar, targeting studies published between 2013 and 2023. Keywords such as "insomnia," "sleep disorders," "physical health," "mental health," and "risk factors" were used. Out of the fifty articles identified, 21 were included in this study. The findings reveal a high prevalence of insomnia among adults, with adverse effects on physical and mental health, including increased risks for cardiovascular disease, metabolic issues, impaired immune function, and chronic pain. The study underscores the bidirectional relationship between insomnia and health, where insomnia can lead to or worsen physical and mental health disorders, which, in turn, negatively affect sleep quality. Moreover, insomnia is closely associated with mental health issues such as depression, anxiety, and substance abuse. The review identifies several risk factors for insomnia, including sociodemographic factors (e.g., older age, female gender), lifestyle habits (e.g., sedentary behavior, irregular sleep patterns), comorbidities (e.g., chronic pain, mental health disorders), and psychological factors (e.g., stress, trauma history). It also highlights the role of genetic and environmental factors in the susceptibility to insomnia. The analysis concludes by emphasizing the critical need for comprehensive evaluations and treatments of insomnia to improve overall adult health.