Mixing authority and alcohol is a very bad thing to do. As Bathsheba gave her counsel to Solomon her son, she made clear to him that this was the case. She said clearly to him that is was not for kings to drink wine or to desire strong drink. These two terms, wine and strong drink both describe alcoholic drinks. Wine refers to the fruit of the vine - grapes - but in the form of them squeezed and made into wine of a lower alcohol level. Strong drink refers to drinks that are much stronger - probably something akin to whiskey or some type of grain alcohol. It was usually used to get drunk quickly - and in some cases was used medicinally to act as a type of pain killer.
Solomon is told that it is not right for a king to drink these things. The reason that she gives to him for this prohibition is that if he does, there is a chance that he will drink and forget "what is decreed." This is a reference to the Word of God. For Israel, the Word of God was also the place where their civil law was found. But either way the concern was that while in a drunken state, he might forget the civil law - or the law of God. When he did, he would then forget the rights of the afflicted. These are the less fortunate, the poor, and those who look to the king to defend their rights.
Drunkenness causes us to function apart from wisdom. When a man is drunk he does not think normally. The alcohol leads him to excess in regard to his emotions. It can also have a deadening effect when it comes to his normal moral restraints. This is why it is not wise to mix drink and authority. When you do, the person in authority is more likely to abuse it - because he will not be thinking properly so as to make godly judgments.