Multiple Drug Use Epidemiology, Correlates, and Consequences


The initial focus is on the conceptual issues essential to the understanding of multiple drug use. This is followed by a discussion of the developmental nature of multiple drug use and the various strategies that have been designed to measure multiple use. The third section of the paper contains a review of the extent of multiple drug use in various segments of society with data from the Monitoring-the-Future surveys of high school seniors, the National Survey on Drug Abuse, and the Treatment Outcome Prospective Study of drug abuse treatment clients. The conclusion is that multiple drug use is pervasive. The next section deals with several consequences associated with multiple drug use: automobile accidents, delinquency, and emergency room visits. The final section outlines some of the prevention and treatment implications of multiple drug use from a public policy perspective.

In a study of the effects of a single drug upon behavior, the implications are manifold. Dosage levels, modes of administration, baseline states, the expectations of the subjects and of the investigators, the environment in which the drug is taken — all these variables, and others as well, make human psychochemical studies difficult and complex. When two or more drugs are used together or in sequence, the problems become magnified. Add to this analysis the vagaries of street drugs with their contaminants, adulterants, diluents, and haphazard quality and quantity control, and the situation almost defies scientific scrutiny. Nevertheless, since polydrug use is notably prevalent and shows no signs of becoming less so, an effort must be made to estimate the impact of multiple drug abuse.

Of all polydrug patterns, those involving alcohol are the most frequently encountered and, perhaps, the most dangerous. The days when substance abusers were categorically labelled — as alcoholic, cokehead, hophead, pothead, and pillhead — seem to be rapidly disappearing. Instead, we are seeing people overinvolved with a primary substance of choice, but also using a variety of others depending on availability, price, social situation, peer group usage, and the latest wisdom from the so-called underground press.

This 1979 statement by Sidney Cohen of the difficulties and complexities inherent in studying the impact of one drug upon the human organism, and the multipliers that must be employed when multiple substances are involved, was a realistic appraisal of some of the more formidable challenges facing scientists in the drug abuse field in the 1980s.

There is an understandable tendency in this field to link research studies and findings to pharmacologically defined categories of drugs. After all, each substance has certain known chemical properties and fits into a particular class of substances with known effects on various systems of the human body. Given the difficulties inherent in studying drug effect, it is not surprising that most laboratory work with drug effects focuses on what happens when specific drugs are ingested in specific regimens by specific routes of administration. This kind of basic research is at the cutting edge of methodology in the drug abuse field. However, human ingestion of drugs, as Cohen notes, is not particulary consonant with the milieu of research laboratories. There is substantial evidence that multiple drug use has been around for quite awhile, and that its incidence and prevalence has been increasing in the past 10 or 15 years. Furthermore, it is known that some multiple drug use is indiscriminant and that it is not unusual for drugs such as marijuana to be “laced” with other drugs such as PCP.

The purposes of this chapter are: (1) to identify some of the conceptual elements that must be addressed in discussing multiple drug use; (2) to discuss some of the measurement issues and confounding variables that may make the study of multiple drug use difficult; (3) to review some of the existing epidemiological data concerning multiple drug use; (4) to discuss some of the problems inherent in untangling the causes of consequences that may be attributable to multiple drug use; and (5) to examine, albeit briefly, some of the policy implications of multiple drug use.

Conceptual Issues in Multiple Drug Use/Abuse

Use versus Abuse

There is at least one generic conceptual issue that emerges in any discussion of drugs — the distinction between “use” and “abuse.” In recognition of the illegal status of some drugs, defining any use of these drugs as abuse is not without logical foundation. However, the drugs lumped together under the rubric of “illegal” differ from each other on many dimensions, including addictive potential and the potential health and other hazards that may result from ingestion of the substance. For these and other reasons, the binary categorization (use versus no use) is inadequate. Instead, it is necessary to conceptualize and operationalize differing levels of involvement with each drug and subsequently to represent the levels of involvement with multiple substances for each individual being studied. The difficulty here is to identify the criteria that will be used to determine what is and what is not abuse (see section on measuring the developmental nature of multiple drug use).

Sequential versus Concurrent Use/Abuse

Much of the writing to date on multiple drug use is based on cross-sectional samples and retrospective life-history interviews. Separate questions are asked for each drug class, usually with regard to lifetime extent of use defined as number of times or number of occasions and then age at onset. It is thus possible to determine the “temporal order” in which various drugs were used on a pair wise basis (alcohol and cigarettes, alcohol and marijuana, alcohol and cocaine, cigarettes and marijuana, cigarettes and cocaine, etc.) by cross-tabulating the age at onset of use of one drug with the age at onset of use of the other drugs. This provides an assessment of the sequential order of onset of use for those persons who have “ever” used various pairs of drugs (i.e., sequential use of multiple drugs). While potentially useful, analyses of sequential order of onset are usually employed to confirm the developmental nature of involvement with drugs rather than multiple drug use.

In retrospective life-history interviews the investigators are often interested in drug usage during a particular period of time (i.e., a specific year). If the respondents are asked if they used each of several drugs during that time period, it would be possible to differentiate the concurrent multiple users from those who have used only one substance. This comes closer to the nominal definition of multiple drug use: simultaneous use of various substances or use of multiple substances during the same drug-using episode or occasion. It should be noted that acceptance of this definition does not mean the definition of sequential involvement with drugs as multiple drug use is inappropriate.

Reasons for Simultaneous Multiple Drug Use

There are at least four primary reasons for simultaneous multiple drug use: (1) to enhance the effects of another drug; (2) to counteract the effects of another drug; (3) as a substitute for preferred drugs that are not available; and (4) to conform to normative ways of using drugs. While it is clear that some people engage in what has been called the “garbage head” syndrome, they are a small proportion of the overall population of drug users. The most common reason for simultaneous multiple use of drugs is to enhance effects. For example, use of other classes of depressants (narcotics, sedatives, minor tranquilizers, or volatile solvents) along with alcohol will add to or enhance the depressant action. There are some drugs that are supraadditive (e.g., the effect is greater than the sum of their doses) that are used for enhancement purposes in multiple drug use. Examples of this kind of potentiating effect are alcohol and barbiturates (only for the nontolerant person or for the chronic user of alcohol who is actively drinking), alcohol and methaqualone, and alcohol and sedatives. Multiple drug use also occurs commonly in the context of counteracting effects. For example, a person who is “wired” because of use of amphetamines may use alcohol to reduce the jittery feeling, just as the cocaine user may “speedball” with heroin to counteract or balance the effects. The third reason for simultaneous use of multiple substances is substitution. Given the vagaries of the supply of drugs, there may be times when the preferred drug is simply not available. At that point a heavy user of a drug such as heroin may substitute codeine-based cough syrup, propoxyphene (Darvon), alcohol, and marijuana — alone or in combinations to carry him over until the supply and/or the quality of heroin available increases. The fourth reason for multiple drug use is normative influences. For example, the prevalence of alcohol and marijuana is so high that it is common practice for the two drugs to be used together — combined use is “normative.”

Measuring the Developmental Nature of Multiple Drug Use

The Epidemiology of Multiple Drug Use

The Consequences of Multiple Drug Use: Untangling the Causes

What are the consequences of drug use and abuse? Even a brief perusal of the literature reveals that virtually every discussion of drug consequences is limited to specific consequences for specific drugs. More often than not, these discussions reify the common sense types of causal attributions that would be made by laypersons. For example, it is often assumed that alcohol is the causal factor in a motor vehicle accident if the driver has a blood alcohol content score above the “minimum” level. Likewise, it is often assumed that marijuana is the causal factor in the lack of motivation shown by students who are “stoned” in the classroom. Our commonsense notions about the consequences of drug use and abuse often contain substantial truth. However, attribution of consequences to the drug “most likely” to be involved is different from attempting to determine the proportion of the consequence attributable to one drug and the proporion attributable to other drugs being used simultaneously. Multiple drugs may mean multiple causes of impairment or exacerbated impairment over and above the level of impairment that would result had only one drug been used. Thus, when one is trying to explain decrements in pulmonary functions, it is important to ask what proportion of the decrement is due to long-term regular use of cigarettes, to chronic marijuana use, to the smoking of free base of cocaine, to environmental hazards, and to genetic propensities.

It is not unusual in the drug and alcohol fields to devote more attention to identifying the consequences than to specifying the independent or causal variable(s). As noted above, the causal variable is often determined a priori because of the dependent variable and its assumed cause.

With what is now known about multiple drug use, perhaps far more attention should be devoted to identifying, measuring, and incorporating multiple drug use patterns into the nexus of predictor variables that are drug related. Measurement of patterns of use of individual drugs is still important. However, the point being made here is for greater emphasis on the fact of multiple use as well as on patterns of multiple use. Our understanding of the consequences of drug use and abuse will increase substantially when we begin to untangle the drug-based causes.

Consequences of Multiple Drug Use: Specifying the Causes

Policy Implications of Multiple Drug Use


Selections from the book: “Recent Developments in Alcoholism. Volume 4: Combined Alcohol and Drug Abuse. Typologies of Alcoholics. The Withdrawal Syndrome. Renal and Electrolyte Consequences.” Edited by Marc Galanter. An Official Publication of the American Medical Society on Alcoholism, the Research Society on Alcoholism, and the National Council on Alcoholism. 1986.