When alcohol is in the system, the liver does its job of breaking it down into acid. From there, the rest of your body starts responding: your brain releases serotonin, the cells communicate more slowly, and you begin to feel the effects.
It takes about an hour for your liver to break down the amount of alcohol in a standard alcoholic drink (one beer, one glass of wine, or one shot). If you drink alcohol faster than your liver can break it down, your blood alcohol level rises and you start feeling drunk.