Background: Longitudinal research on COVID-19 impacts on drinking is scarce and largely restricted to comparing drinking levels before and after the introduction of COVID mitigation measures. This brief snapshot of behavior ignores the extended pre-COVID drinking trajectory, which may be decreasing increasing, or remaining stable over time. Behavioral economics predicts that pandemic-related constraints on behavioral alternatives to alcohol and drug use, and decreased constraints on alcohol, may result in increases in drinking at later stages of the pandemic. Therefore, the current study characterized drinking trajectories among emerging adults before and during the pandemic and investigated time-invariant demographic predictors and time-varying behavioral economic predictors of trajectories of drinking and behavioral economic variables. Methods: A pandemic-focused survey was distributed between May 15 and June 29, 2020 to emerging adults participating in an ongoing longitudinal study involving pre-COVID data collection every four months. Participants with four pre-COVID assessments were included in the current study (N = 312, ages 21.5-24 years; 65.1% female). Results: Linear piecewise models best fit the drinking days and drinks per week data, suggesting a pandemic-related disruption of ongoing drinking trajectories. After controlling for all other time-invariant predictors, lower environmental reward was associated with greater increases in heavy drinking days and income loss was associated with lower drinking days, drinks, and heavy drinking days per week. In parallel LGCM models, increases in alcohol demand indices were generally associated with increases in drinking from the pre- to the post-COVID onset timepoint. Conclusions: The results suggest that the pandemic attenuated ongoing declines in drinking trajectories and highlight the value of examining trajectories to characterize COVID-19-related effects. Behavioral economic measures of environmental and alcohol reward may be useful predictors of changing alcohol use patterns, particularly in the context of emergent public health crises.