Much of the research on posttraumatic stress disorder (PTSD) and alcohol use disorder (AUD) has been conducted in high-income countries (HICs). However, PTSD and AUD commonly co-occur (PTSD þ AUD) are both associated with high global burden of disease, and disproportionately impact those in low-and middle-income countries (LMICs). This narrative review attempts to synthesize the research on prevalence, impact, etiological models, and treatment of PTSD þ AUD drawing from research conducted in

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... s and discussing the research that has been conducted to date in LMICs. The review also discusses overall limitations in the field, including a lack of research on PTSD þ AUD outside of HICs, issues with measurement of key constructs, and limitations in sampling strategies across comorbidity studies. Future directions are discussed, including a need for rigorous research studies conducted in LMICs that focus on both etiological mechanisms and on treatment approaches. Impact statement Despite the fact that the majority of the world's population lives in low-and middle-income countries (LMICs), most of the research on the co-occurrence of posttraumatic stress disorder (PTSD) and alcohol use disorder (AUD) comes from data on samples from high-income countries. This review entailed a targeted examination of the existing literature on the prevalence, consequences, etiology, and treatment of comorbid PTSD þ AUD derived from LMICs. Emphasis is placed on a need for more research on the epidemiology, etiology, and treatment of PTSD þ AUD in LMICs. It further offers guidance based on the data thus far for how to conduct this research in methodologically sound, resource-sustainable, and culturally relevant ways. Due to strong, consistent associations between posttraumatic stress disorder (PTSD) and alcohol use disorder (AUD), their co-occurrence (PTSD þ AUD) has been a topic of extensive study (Pietrzak et al., 2011; Smith and Cottler, 2018) . Data from 42 studies conducted primarily in the USA and other high-income countries (HICs) estimate that 10-61% of people with PTSD also misuse alcohol. Among people with AUD, an estimated 2-63% was found to have co-occurring PTSD (Debell et al., 2014) . Studies examining variation in the presentation of PTSD þ AUD have found that it is generally associated with more severe PTSD symptoms and higher rates of drinking relapse (McCarthy and Petrakis, 2010; Debell et al., 2014; Smith and Cottler, 2018) . However, these findings are largely based on research conducted in HICs, and overall there is a dearth of research on the onset, course, and treatment of comorbid PTSD and AUD in low-and middle-income countries (LMICs; Seedat and Suliman, 2018). This is problematic, given that the majority of the world's population resides in LMICs (Jacob et al., 2007) . Global burden of PTSD and AUD Individually, PTSD and AUD present major public health burdens and are associated with high rates of functional impairment. Mental health and substance use disorders (SUDs) are the highest contributors to years lived with disability globally (Whiteford et al., 2013) . Alcohol use is the Cambridge Prisms: Global Mental Health www.cambridge.org/gmh