The common theory is that the alcohol interferes with the signals in our "higher" brain. Although, recently I read that they effects are contributed to an enzyme produced by the body to deal with the alcohol, not the alcohol itself. Whichever the case, signals are being affected within the brain.
New US research found that women have lower levels of the stomach enzyme that breaks down alcohol before it is absorbed into the bloodstream. This means that women are ineffective at breaking down high concentrations of alcohol in drinks stronger than beer. This could explain why women are more prone to getting drunk than men.