A critical review of front-loading: A maladaptive drinking pattern driven by alcohol's rewarding effects

Abstract

Front-loading is a drinking pattern in which alcohol intake is skewed toward the onset of reward access. This phenomenon has been reported across several different alcohol self-administration protocols in a wide variety of species, including humans. The hypothesis of the current review is that front-loading emerges in response to the rewarding effects of alcohol and can be used to measure the motivation to consume alcohol. Alternative or additional hypotheses that we consider and contrast with the main hypothesis are that: (1) front-loading is directed at overcoming behavioral and/or metabolic tolerance and (2) front-loading is driven by negative reinforcement. Evidence for each of these explanations is reviewed. We also consider how front-loading has been evaluated statistically in previous research and make recommendations for defining this intake pattern in future studies. Because front-loading may predict long-term maladaptive alcohol drinking patterns leading to the development of alcohol use disorder (AUD), several future directions are proposed to elucidate the relationship between front-loading and AUD.

Keywords: alcohol; alcohol use disorder; drinking patterns; front-loading; high-intensity drinking; motivation; tolerance.

FIGURE 1

Example drinking distributions which have been categorized using the described change point analysis. (A) Front‐loading, where the drinking pattern meets all suggested criteria: (1) the strongest change point is the earliest detected change point, (2) the pre‐change point slope is significantly greater than the post‐change point slope and (3) the pre‐change point slope is greater than the rate of metabolism. (B) Not front‐loading, as the pre‐change point slope does not differ from the post‐change point slope; i.e., there is no evidence for a skew toward the onset of access. (C) Not front‐loading, as the pre‐change point slope is not greater than the rate of metabolism. (D) An inconclusive result. Inconclusive drinking patterns display a high rate of consumption at the end of the session, which is greater than any early drinking rate. However, note in this example that there is still a considerable amount of intake in the beginning of the session. Users of this analysis should consider the most clinically and experimentally relevant definition of front‐loading when determining whether front‐loading occurred. The categorizations determined by this code are only meant to serve as suggestions.