What's one drink?

One drink is defined as:*

  • 12 ounces (one bottle/can) of beer or wine cooler
  • 5 ounces (one glass) of wine
  • 1.5 ounces (one shot) of 80-proof distilled spirits

*Source: NIAAA

Alcohol and the Brain

Most of us have witnessed the outward signs of heavy drinking: the stumbling walk, slurred words and memory lapses. People who have been drinking have trouble with their balance, judgment and coordination. They react slowly to stimuli, which is why drinking before driving is so dangerous. All of these physical signs occur because of the way alcohol affects the brain and central nervous system.

Alcohol affects brain chemistry by altering levels of neurotransmitters. Neurotransmitters are chemical messengers that transmit the signals throughout the body that control thought processes, behavior and emotion. Neurotransmitters are either excitatory, meaning that they stimulate brain electrical activity, or inhibitory, meaning that they decrease brain electrical activity. Alcohol increases the effects of the inhibitory neurotransmitter GABA in the brain. GABA causes the sluggish movements and slurred speech that often occur in alcoholics. At the same time, alcohol inhibits the excitatory neurotransmitter glutamate. Suppressing this stimulant results in a similar type of physiological slowdown. In addition to increasing the GABA and decreasing the glutamate in the brain, alcohol increases the amount of the chemical dopamine in the brain's reward center, which creates the feeling of pleasure that occurs when someone takes a drink.

Summary of alcohol's effects on the brain - Move your cursor over the colored bar in the lower left-hand corner to see which areas of the brain are affected by increasing BAC.

Alcohol affects the different regions of the brain in different ways:

  • Cerebral cortex: In this region, where thought processing and consciousness are centered, alcohol depresses the behavioral inhibitory centers, making the person less inhibited; it slows down the processing of information from the eyes, ears, mouth and other senses; and it inhibits the thought processes, making it difficult to think clearly.
  • Cerebellum: Alcohol affects this center of movement and balance, resulting in the staggering, off-balance swagger we associate with the so-called "falling-down drunk."
  • Hypothalamus and pituitary: The hypothalamus and pituitary coordinate automatic brain functions and hormone release. Alcohol depresses nerve centers in the hypothalamus that control sexual arousal and performance. Although sexual urge may increase, sexual performance decreases.
  • Medulla: This area of the brain handles such automatic functions as breathing, consciousness and body temperature. By acting on the medulla, alcohol induces sleepiness. It can also slow breathing and lower body temperature, which can be life threatening.

In the short term, alcohol can cause blackouts -- short-term memory lapses in which people forget what occurred over entire stretches of time. The long-term effects on the brain can be even more damaging.