How to prevent a hangover ?

None proven: Every study, so far, of dozens of hangover cures have not shown any to work consistently in most people. A recent study out of china said that they found sprite to be helpful in hangovers, but i haven't read the study, and can't vouch for it. Staying well-hydrated (getting drunk dehydrates you), using tylenol (acetaminophen) for headache and giving it time is mostly the best we can do. Drinking less prevents it.