The relationship between withdrawal and addiction may confuse people because most genuine addicts do experience withdrawal of some sort when they quit, and most scientists think that avoiding withdrawal is one reason addicts keep using the substance to which they are addicted. Alcohol is a good example of how tolerance and withdrawal contribute to addiction. If a person drinks heavily for a long time, his brain will adapt to the sedative effects of the alcohol. The compensation that happens is like the caffeine example above, only with a different neurotransmitter. Alcohol activates receptors in the brain for the neurotransmitter GABA, which normally inhibits brain activity. After long-term alcohol exposure (weeks to months or years), the brain compensates by diminishing the ability of these receptors to function. The alcoholic is now tolerant to the alcohol, just as the coffee drinker was tolerant to caffeine.