Does alcohol cause any vitamin deficiences? if so how do i know if i need to take extra supplements?

Yes: Alcoholism is associated with, among other things, B12 and Folic Acid deficiencies. You should not, however, have a problem if you eat right, exercise, and drink alcohol only in moderation. If you are an alcoholic then vitamin deficiency is only a part of the problem, and the problems won't improve until the alcohol abuse stops no matter how many supplements you take.

Yes: Alcohol depletes the body of many vitamins, especially thiamine (vitamin b1), folic acid, and pyridoxine (b6), and may also reduce vitamins c and d. People in recovery are generally recommended to take thiamine 100 mg, Folic Acid 1-2 mg and a general supplement (one a day, centrum etc.). The most important thing is to stop drinking, if you are drinking to excess. See your doctor or a counselor.