Aversive Effects of Alcohol and Nicotine

by National Institute of Health

(Page 3 of 6)

Both alcohol and nicotine frequently have unpleasant effects that are aversive (nausea) and which depend on the dose of and previous experience with the drug. For both drugs, the aversive properties, at least in part, result from irritation of the stomach. Some of alcohol's unpleasant effects are caused by acetaldehyde, the first breakdown product (metabolite) of alcohol. However, these two factors may not explain all the aversive effects of nicotine and alcohol. The development of tolerance to these aversive effects may be a contributing factor in the continued use of both alcohol and nicotine. Laboratory evidence suggests that administration of either alcohol or nicotine and development of tolerance to its aversive effects can also decrease the conditioned taste aversion to the other drug. If confirmed in humans, this phenomenon, which is called crosstolerance, may have important implications for the combined use of nicotine and alcohol in humans.

Impulsivity and Sensation Seeking

Two additional factors involved in the initiation of drug use are impulsivity and sensation seeking. The term "impulsivity" describes an individual's tendency to make rapid behavioral changes regardless of detrimental consequences or the loss of a later reward of greater magnitude (taking a drug despite knowing the potential adverse effects on health or wealth). In laboratory animals, researchers can measure the degree of impulsivity by comparing whether rodents preferentially press a lever to receive a larger, delayed food reward or a smaller, rapidly available reward. Another strategy to assess impulsivity (called differential reinforcement of low rate responding [DLR]) involves tests in which low rates of responding are selectively rewarded. Researchers have identified several different forms of impulsivity, at least some of which involve reduced transmission of nerve signals involving the neurotransmitter 5-HT (also known as serotonin).

The association between impulsivity and alcohol and nicotine use has two important aspects. The first aspect is the extent to which an individual's innate impulsive behavior results in increased alcohol or nicotine use, often despite knowledge of the adverse consequences. Dependence on both alcohol and on nicotine has been found to be associated with high levels of impulsivity. This impulsivity is thought to contribute to the person's initial use of the drugs and possibly to the development of dependence. The second aspect is the propensity of the drugs themselves to increase impulsivity. There is little direct evidence that nicotine affects impulsivity. Alcohol consumption has resulted in increases in measurements of impulsivity. An increase in impulsive behavior caused by alcohol consumption would be expected to increase cigarette smoking during drinking.

Sensation seeking is defined as an individual's desire for novel or arousing experiences. Studies in humans have found strong correlations between high ratings of sensation seeking and experimental use of drugs, including alcohol and nicotine. It is as yet unclear whether sensation seeking also promotes the concurrent use of alcohol and nicotine, although this appears likely. Similarly, researchers have not yet identified the neurochemical basis of the association between sensation seeking and drug use. It has been suggested that brain signaling pathways involving the neurotransmitters dopamine and serotonin may play a role. In addition, the effects of alcohol and nicotine on stress hormones may be involved both in the initial use of these drugs in an experimental way - for example, by adolescents - and in the continued drug use during dependence.

Mechanisms of Dependence

The American Psychiatric Association has defined specific criteria for a diagnosis of dependence in its Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV). These criteria include the development of tolerance and the appearance of withdrawal symptoms when drug consumption is discontinued after prolonged heavy use. Other criteria describe the pattern of compulsive use that is the predominant characteristic of dependence on drugs, together with its long-term nature. Thus, addicts can revert to drug taking and frequently experience all the symptoms of dependence after weeks, months, or even years of abstinence. Such relapse occurs with both alcohol and nicotine, and it is important from a clinical perspective to know whether the continued use of one drug affects the patient's success in abstaining from the other drug. For example, alcoholics attempting to abstain from alcohol most commonly continue smoking. Accordingly, clinicians need to know whether this continued smoking has adverse effects on abstinence from alcohol, as might be the case if there are common mechanisms of dependence, or whether the difficulties of giving up smoking in addition to alcohol may make life harder and create a more stressful situation for the alcoholic. No extensive evidence regarding these issues exists to date; however, several studies have indicated that giving up smoking as well as drinking does not reduce abstinence rates from alcohol and that it may actually be beneficial to abstain from both alcohol and nicotine simultaneously.

Researchers must learn more about the mechanisms underlying the dependence on alcohol and nicotine to maximize the success of treatment for both addictions. Some of those mechanisms are described in the following sections.

About the Author

NIH is the nation's medical research agency - making important medical discoveries that improve health and save lives. The National Institutes of Health (NIH), a part of the U.S. Department of Health and Human Services, is the primary Federal agency for conducting and supporting medical research.