Behavioral mechanisms underlying the link between smoking and drinking

Abstract

Many people use both alcohol and nicotine (i.e., cigarettes and other tobacco products). The behavioral effects of these two drugs differ, and they do not act on the same target sites in the brain, although they may share, or partly share, certain properties. The initiation of alcohol or nicotine use may be precipitated by similar personality characteristics in the user, such as impulsivity and sensation seeking. Moreover, the mechanisms underlying the development of dependence may be similar for alcohol and nicotine. Thus, certain factors, such as reinforcing drug effects, conditioning processes, automatic behavior, and stress, may influence the development of dependence on both drugs. Other factors, such as tolerance and sensitization to the drugs' actions and the development of withdrawal symptoms, may also contribute to dependence. This review discusses the actions of the two drugs on certain brain chemical (i.e., neurotransmitter) systems and the extent to which the effects of the two drugs may interact.

Figure 1

Reasons for and consequences of initial use of alcohol (A) and tobacco (i.e., nicotine) (B). Several factors can motivate a person to drink or smoke during the initial phase (i.e., the first few times) of alcohol or tobacco use. Among drinkers, the majority of people develop a pattern of social drinking; only a minority of drinkers becomes dependent on alcohol. Conversely, the vast majority of smokers become nicotine dependent; only a few smokers maintain a pattern of social use. The thickness of the arrows reflects the proportion of people that develop the drinking and smoking patterns indicated.

Figure 2

Consequences of continued alcohol and tobacco (i.e., nicotine) use. During the initial use of alcohol and tobacco, changes in the activity of nerve cells (i.e., neuroadaptive changes) occur, resulting in reinforcement and habit formation. These changes lead to repeated social use, which may result in dependence in some people. In those people, sudden abstinence from alcohol or nicotine leads to withdrawal symptoms, which cease during prolonged abstinence. However, even after prolonged abstinence, relapse may occur.

Figure 3

Effects of alcohol and nicotine on the mesolimbic dopamine system. Dopamine is a brain chemical believed to play an important role in addiction. The mesolimbic dopamine system includes three brain regions: the ventral tegmental area, nucleus accumbens, and prefrontal cortex. The ventral tegmental area contains dopamine-releasing nerve cells (i.e., neurons). The extensions of those neurons lead into the nucleus accumbens and prefrontal cortex, where they release dopamine to activate other neurons. The actions of alcohol and nicotine in these brain areas are shown in italic.