When it comes to hangovers, bartenders have seen it all. It doesn't matter if they're fighting their own hangover demons or dealing with sluggish customers who are trying to avoid the light during brunch service: bartenders become natural experts on the topic due to their work. Rico Wisner of BLT Steak is one such expert. This is what he tells his customers about avoiding hangovers. It's advice he uses himself.
I'm a believer in a preventative approach when possible. A friend of mine turned me on to milk thistle. It's a supplement that's supposed to be good for your liver. I take that before going drinking. Combine that with a Gatorade before bed and it's usually not bad. Otherwise if it's too late and I have a hangover, I go with a good quality ginger ale like Q, and a good dose of bitters. If it's really bad, a shot of Fernet.