The term “harm per litre” has been increasingly used in alcohol research in recent years as a concept and a comparative measure of alcohol-attributable harm in comparisons between environments, circumstances, and patterns of drinking. This essay discusses the origins of the term in connection with analyses in terms of patterns as well as levels of drinking and with concerns about differential harms from drinking different beverage types. Also discussed is the term's current primary usage, in the context of epidemiological concerns about differentially severe harms for poorer persons who drink. It is noted that these same concerns have been discussed, particularly in Britain, using the phrase “alcohol harm paradox”.

“Harm per litre” was initially most often used in comparisons between rates of alcohol-attributable harm by beverage type. After 2010, the expression was applied more broadly, particularly after its use in various World Health Organization-related discussions and documents. In addition, and especially from 2018 onwards when most of the papers using this term were published, it has been used in comparisons by socioeconomic status at the individual level, and by level of socioeconomic development at the country level. Almost all the findings indicate that people with lower socioeconomic status, and countries with lower average income, e.g., low income and lower-middle income countries, incur considerably higher harm per litre (with harm being expressed in disease burden and mortality) than upper middle-income and high-income countries.

“Harm per litre” is a practicable and easy-to-understand concept to compare groups of individuals or countries, and to quantify health inequalities. The next important step will need to be elucidating a better causal understanding of the processes underlying these inequalities, with an emphasis on factors which can be most easily changed by interventions.