Dark drinks, like red wine and bourbon, have more congeners than light ones and there are several studies to show that for a given level of blood alcohol, dark drinks produce worse hangovers. But outside of the laboratory, the worst hangover will come from whatever causes you to drink the most.

Scientifically speaking, darker spirits like bourbon, brandy, and red wine are notorious for causing the worst hangovers. This is due to a high concentration of congeners—complex organic molecules like methanol, tannins, and acetone that are byproducts of the fermentation and aging process. A landmark study comparing bourbon and vodka found that while both impair sleep and performance similarly, the high congener count in bourbon (about 37 times that of vodka) leads to significantly more severe headache, nausea, and thirst the next day. Champagne and carbonated mixers also rank highly on the "misery scale" because the bubbles accelerate the absorption of alcohol into the bloodstream, leading to a faster and more intense spike in blood alcohol levels. Conversely, clear spirits like high-quality vodka and gin contain fewer impurities and generally result in milder symptoms, provided they aren't consumed in excess. Ultimately, while the "congener theory" holds true, the most reliable predictor of a hangover remains the total volume of ethanol consumed and your level of hydration during the night.