When a person drinks alcohol repeatedly, it takes more drinks to become intoxicated. This means that the person has developed tolerance to alcohol. Tolerance is a consequence of two changes in the body. With repeated use of alcohol, the targets (i.e., GABA receptors) for alcohol adapt by decreasing their number. Now, it’s harder for alcohol to produce its effects. Interestingly, one effect that does not show alcohol tolerance is death. In fact our biological defense mechanisms promote “passing out” from too much alcohol to protect against death. Unfortunately, drinking too much too fast increases the BAC to a lethal level, bypassing tolerance.
Second, liver cells respond by making more enzymes to metabolize alcohol. The increased metabolism means there is less alcohol in the body. In both of these situations, the person will drink more alcohol to try and achieve the original effect. These cellular adaptations and the development of tolerance are key to the progression to addiction.
Researchers have shown that repeated episodes of binging and drinking to intoxication substantially increases the risk of alcohol addiction (now called alcohol use disorder). Once the person is addicted to alcohol, he/she no longer has control over drinking. The loss of control and craving that ensues when the alcohol isn’t available are due to changes that take place in the brain.
One serious change that can result from repeated drinking is shrinkage of the brain. The shrinkage is probably due to a loss of neurons (grey matter) and glial cells (white matter), the other major type of cell in the brain. The shrinkage happens especially in areas of the brain that are important in learning and memory, such as the cerebral cortex and the hippocampus.
Figure 2.6 Brain scans (magnetic resonance imaging or MRI) show a smaller hippocampus (in the red circles) in a person with adolescent alcohol-use disorder (right) compared to a healthy person of the same age (left). (Adapted from M.D. De Bellis, with permission). Learn how an MRI is obtained.