Is there some standard to use as proof (or conversely a defense) in such a case of alcoholism or drug addiction?

Let’s say the wife claims her husband is an alcoholic who is in a stupor most of the time. She maintains that he is a staggering drunk; he admits that he imbibes now and then.

In those states that retain addiction or drunkenness as grounds for divorce, the addiction must be a fixed, long-term habit that occurs regularly or often.

Mere occasional or moderate drinking is usually not sufficient and even binges and lost weekends may not be arguable in supporting a claim of alcoholism. A "functioning" alcoholic -- one who holds on to his job despite regular weekends lost in alcoholic stupor -- may also be difficult. These domestic situations, absent objective evidence, invite he says-she says testimony.

Sadly, the objective evidence that passes muster might include a string of drunk driving convictions or hospitalizations for alcoholism.