The short answer: congeners are chemical byproducts of fermentation and aging that give drinks their flavor and color — and also make hangovers worse. Darker drinks contain far more of them than clear ones.
What congeners actually are
They're a group of compounds — including methanol, acetaldehyde, tannins, and fusel oils — produced as alcohol ferments and ages in barrels. They add character to a whiskey or a red wine, but your body has to process them alongside the alcohol.
Which drinks have the most
Highest: brandy, bourbon, whiskey, and red wine. Lowest: vodka and gin. See the full drink-by-drink ranking.
Why they worsen hangovers
Congeners add to the toxic load your body must clear at the same time it's dealing with acetaldehyde, which can intensify and prolong symptoms. The complete list of hangover causes.
How to limit the hit
Lean toward clearer drinks, pace yourself, hydrate, and pre-load with a Gush. The full prevention guide.
Always drink responsibly. This statement has not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.