Although, the US and UK guidance documents cite a number of, mostly cross-sectional, studies to support the proposed association between earlier AFD and harmful alcohol use in adulthood, a systematic appraisal of the nature and strength of the relationship between AFD and later harmful alcohol use has not previously been performed.3–6 An understanding of this relationship is important to determine the value of preventive interventions in reducing longer term alcohol harms.7 An underlying causal relationship between earlier AFD and adult alcohol problems could exist if there is neurobiological or other developmental impairment or if alcohol involvement is otherwise promoted, for example via peer networks. If any such causal relationship exists, widely delivered early interventions which delay AFD could make a significant contribution to reducing population levels of alcohol problems. If there is no causal relationship, however, delaying age of drinking initiation will not reduce levels of adult alcohol problems, though it may still confer other benefits in relation to adolescent harms.2 Within the research community there has been debate about whether there is an underlying causal relationship between earlier AFD
