This article is from the Depression FAQ, by Cynthia Frazier with numerous contributions by others.
There are a number of problems with the mixture of alcohol and antidepressants. First, antidepressants may make you especially susceptible to the intoxicating effects of alcohol. Second, if you drink more than three or four drinks a week, the effects of alcohol may prevent the antidepressants from working. Many people who seem not to benefit from antidepressants, do so, if they reduce or eliminate their intake of alcohol. Third, you may be taking along with the antidepressant a drug such as clonazepan (Klonopin) with which one should not drink at all.