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Water and sports drinks

Conventional wisdom holds that the dehydration caused by heavy drinking is what makes you feel so sick the next day. In fact, experts actually know very little about what causes a hangover. Potential culprits include disrupted biological rhythms or even alcohol withdrawal, and research suggests that congeners—toxic substances found in alcohol, especially dark liquors such as whiskey—may also play a role.

Nevertheless, replacing the fluid you've lost will likely help you feel a little less miserable. "Juice, water, Gatorade, all those things—they're going to make you feel better," says Dr. Cutler.

Next: Take pain relievers