The fermenting process that transforms corn and other grains into bourbon, and converts potatoes, grains—and increasingly grapes and other elements—into vodka, not only produces alcohol, but also byproducts known as congeners. And, according to research to be published next March in the journal Alcoholism: Clinical and Experimental Research, the concentration of congeners, which can be toxic in large amounts, may impact just how terribly you feel the morning after drinking a particular liquor. Researchers from the Boston University School of Public Health and the University of Michigan Medical School put some science behind what many holiday revelers have long suspected—if sleep and total alcohol consumption are the same, because of its higher concentration of congeners, bourbon gives you a far worse hangover than vodka.

Bourbon, the researchers found, has 37 times the amount of congeners that vodka does, leading researchers to believe that it would cause more painful hangovers. To test this theory, they recruited—and paid—95 men and women to go out drinking. After an initial night of acclimatization, study participants were given drinks containing either bourbon or vodka, and kept swilling away until they reached a blood alcohol content level of .11 (the legal limit is .08). The following night, participants drank the same amount, but of a placebo, or non-alcoholic concoction.

Researchers found that, no matter your poison, drinking to a blood alcohol content level of .11 impedes performance the following day. Yet, what was interesting, they said, was that when they tested people after their blood alcohol content had returned to 0.0 the following day, even though bourbon drinkers still felt a whole lot worse, both they and vodka drinkers had the same level of impairment on tasks.