Alcohol blocks the brain's gas pedal.

To balance the brakes, your brain has a gas pedal chemical called glutamate. This chemical keeps you alert, helps you learn, and keeps your thoughts moving quickly. Alcohol blocks glutamate from doing its job. With the brakes pressed down and the gas pedal blocked, your brain activity plummets. This double-whammy is the reason your reaction times slow down. It is why you cannot catch a keys-drop as fast, and why your speech starts to slur as your brain struggles to coordinate your mouth muscles.