Mixing light and dark liquor may not be necessarily bad, but it can lead to a worse hangover due to the different levels of congeners in each type of alcohol. Congeners are toxic byproducts of the fermentation process that contribute to hangover symptoms. Dark liquors like whiskey, bourbon, and brandy tend to have higher levels of congeners than clear liquors like vodka, gin, and rum. When different types of alcohol are mixed, it can make it harder for the liver to process the congeners, leading to a more severe hangover. Therefore, it’s better to stick to one type of alcohol or mix it with non-alcoholic beverages to minimize the negative impact.