Many people use both alcohol and nicotine (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 (neurotransmitter) systems and the extent to which the effects of the two drugs may interact.

The use of drugs outside clinical medicine is motivated by many factors, including experimentation, peer pressure, self-medication for psychological problems (anxiety and depression), and dependence. Therefore, the strong association between alcohol consumption and cigarette smoking is also likely to be attributable to multiple factors, including pharmacological actions common to both alcohol and nicotine. This article first explores the reasons underlying initiation of drug use, such as the pharmacological effects of alcohol and nicotine, then reviews the behavioral mechanisms involved in alcohol and nicotine dependence. Whenever possible, these discussions highlight the mechanisms that may account for alcohol and nicotine co-dependence.

Behavioral Mechanisms Involved in
the Initiation of Drinking and Smoking

Acute Behavioral Effects of Nicotine and Alcohol

The reasons why most people initially experiment with drugs are related to the drugs' acute pharmacological effects, such as relief of anxiety or stress and induction of euphoria. These effects result from the drugs' actions on various brain chemical (neurotransmitter) systems in the central nervous system. These initial target sites in the CNS for alcohol and nicotine differ in many respects. Nicotine interacts with specific "docking molecules" (protein receptors) on the surface of certain nerve cells (neurons). In contrast, alcohol produces selective actions on several neurotransmitter systems.

The acute behavioral effects of alcohol and nicotine and the interactions between these effects have been described in detail. As with all drugs that act on the CNS, these effects are crucially determined by the dose that is taken, as follows:

At lower doses, nicotine has an alerting effect, resulting in increased attention and improved concentration.

At higher doses, nicotine has been reported to have a depressant effect on mood and arousal, although this effect is not as pronounced as that of alcohol.

Low alcohol doses cause such effects as a decrease in the normal social inhibitory control of behavior, loss of motor control, incoordination, and increased reaction times. These behavioral effects of alcohol generally are not shared by nicotine, with the possible exception of a decrease in inhibitory control of behavior that has been suggested by some experimental results.

Higher alcohol doses have effects ranging from intoxication and sedation to general anesthesia.

The increased ability to concentrate after nicotine ingestion is thought to be one reason underlying its use by humans. Studies in humans have also shown that nicotine decreases the sedative properties of alcohol, an effect that may promote the combined intake of the two drugs.

The possible presence of a withdrawal state and the influence of such a state on measurements must be considered when assessing the acute effects of alcohol and nicotine. This influence may differ for alcohol and nicotine, because the rate with which people develop dependence on these drugs differs. Thus, dependence on nicotine appears to develop rapidly (possibly within months). Moreover, high proportions of people who try nicotine become dependent on it. In contrast, alcohol dependence develops more slowly (normally over several years) and is seen in only a small proportion of people who regularly drink alcohol. Consequently, in studies evaluating the effects of these drugs (in volunteer populations), investigators must consider the extent to which the subjects are dependent on the drugs. For example, people who regularly smoke cigarettes are likely to be dependent on nicotine, and this dependence may influence the effects of nicotine when the volunteers have been asked to stop smoking, even for a couple of days. This finding is particularly relevant to the estimation of the anxiety-reducing and euphoric effects of nicotine. Conversely, many people who use alcohol regularly do not show symptoms of dependence, and thus abstinence from alcohol for a few days will have a lesser influence on the acute actions of alcohol in volunteers.

Tags: Smoking, Alcoholism

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