In summary, alcohol responses were examined in a unique longitudinal framework in heavy drinkers and light drinker controls. Alcohol response differences between these groups observed at initial testing remained 5–6 years later, with greater alcohol stimulating and rewarding effects and lower sedation and cortisol excretion in heavy drinkers. The leading theories of addiction based on animal models were tested in this direct repeated alcohol challenge investigation. Empirical evidence was provided for the early stage of addiction in the allostasis theory with continued heightened alcohol stimulation and reward sensitivity in heavy drinkers with increasing AUD symptoms during the transition of young to early middle adulthood. These sustained pleasurable effects may increase the drive for excessive drinking(34) despite mounting consequences and alcohol problems. At the same time, heavy drinkers with low AUD symptoms indicative of less harmful drinking over time exhibited reduced alcohol stimulation at re-examination while heavy drinkers with intermediate AUD symptoms were largely intermediate on their alcohol responses, i.e., in between the low and high AUD groups in alcohol sensitivity. The combination of changes observed supports alcohol response phenotype as
