WHO has identified nicotine, alcohol, and illicit drugs as among the top 10 contributors of morbidity and mortality in the world. Substance use disorders are preventable conditions that are major contributors to poor health, family dysfunction, and various social problems that have a profound economic impact. Digestive system damage caused by substance intake is an increasing problem among drug addicts. Alcohol abuse is the predominant cause of liver fibrosis and acute and/or chronic pancreatitis. Many studies show that alcohol consumption can cause cancer of all parts of the digestive system. During ethanol intake, the upper GIT is exposed to concentrations of alcohol several times higher than those in other tissues. Therefore, chronic alcoholics may present with GI complaints more commonly than non-alcoholics. This work was designed with the objective to study the histopathological changes in the small intestine of chronic alcoholics, to study the effects of chronic alcohol intake on small intestinal cellular functions with focus on brush border enzymes, membrane enzymes, and cellular enzymes and to study the alterations of small intestinal microecology in chronic alcoholics.