The steady increase in individuals with substance use disorder requiring admission to the intensive care unit (ICU) has been an area of concern, leading to an increase in ICU utilization and costs related to both licit and illicit abuse of these drugs. Most recently, the COVID 19 pandemic has contributed to an increase in substance use and overdoses, with preliminary data suggesting an almost 30% increase in overdose deaths over the course of the pandemic. This increase in prevalence underscores the importance for the critical care practitioners to be knowledgeable about how substance use disorders impact the critically ill patient and understanding the epidemiology of substance use in critically ill patients. Management of patients with substance use disorders is complicated by the associated intoxication and withdrawal syndromes, as well as by the physiologic changes that occur with chronic use that can cause, predispose patients to, and worsen the severity of many conditions. This makes it vital that critical care providers are adept at identifying and treating common intoxication and withdrawal syndromes, as well as proficient at treatment considerations owing to chronic use of such addictive substances. This text provides a comprehensive, state-of-the-art review of the critical care implications of some of the commonly used addiction drugs and serves as a very useful resource for everyone involved in the care of critically ill patients impacted by substance use disorder. It provides a concise yet comprehensive summary of the status of the field that helps guide patient management and stimulate investigative efforts.  All chapters are written by experts in their fields and include the most up to date scientific and clinical information.