Human beings have a widespread and long-standing affinity for alcohol, tobacco, cannabis, opiates and allied substances. Most people are in some way drug users and the value of such substances is underlined by the voracious demand for them. Sadly, humans are not always rational or careful in their ways. Drug taking is all too often complicated by inappropriate or harmful use. It is doubtful if there is any such entity as a "safe drug". Even the most familiar and innocuous substance appears to be used in a harmful manner by some people, even if these constitute only a small minority of users. "Drug misuse", "drug problems" or "drug abuse" appear to be the inevitable price that is incurred by humanity's liking for chemical methods of mood adaptation. At its most extreme such misuse is illustrated by the plight and dereliction of Skid Row meths drinkers, the misery of housewives unable to face another day without yet another prescription for tranquillizers, the middle-aged smoker dying from lung cancer and emphysema or of the young man or woman dying of AIDS contracted by the sharing of infected injecting equipment or by unprotected sexual contact.

Equally tragic is the toll of injury and death inflicted by alcohol-related accidents and violence. In fact, drug use does not occur in isolation and the precise role of drugs, legal or illegal, in specific health or social problems is often unclear. For example, it has been alleged that young soccer fans fight because they have been drinking: plenty of people drink without fighting and alcohol consumption is not in itself an adequate explanation for violence, even if it is frequently an associated or possible contributory factor.

Legal and illegal drug use have long been linked with sexuality for a host of reasons. These include social and cultural as well as psychological and physiological factors. Drinking is commonly associated with dating and with sexual encounters. So too are a number of "illicit drugs", albeit on a less popular or widespread basis.

During recent years the connection between "risky sex" and psychoactive drugs has been accorded vastly added seriousness by the advent of the AIDS epidemic. This is not the first time that humanity has been confronted by the specter of a sexually transmitted disease which is incurable and fatal. Even so, while the search for a "cure" for AIDS continues, particular attention is, quite logically, being paid to determining which factors foster the spread of HIV infection and to possible ways of curbing such spread. Since the upsurge of HIV infection in industrial countries it has been obvious that intravenous drug use, in particular the sharing of infected injecting equipment, is a major risk factor. More recently, attention has been drawn to the possible role of alcohol and other "disinhibiting" substances in relation to high risk or unprotected sex.

The review that is presented of alcohol, tobacco and illicit drug use and related problems is written from a largely British perspective. Even so, it is hoped that when appropriate more general information is also cited, especially in the consideration of the crucial, practical topics of "prevention" and "harm minimization".

"Drugs" are frequently portrayed by the mass media as inherently harmful, injurious and malign. This impression, reasonably enough, is clearly reinforced by stereotypes of the casualties of various form of damaging drug use. Such stereotypes, the "wino", the "alcoholic" and "the junkie", are frequently held up as cautionary representations, and combined with warnings about the perils of excess or deviant forms of drug use. Simple images often beget simple solutions. Messages such as "Just Say No!" have both clarity and a popular appeal. In fact, neither drug use nor other health-related behaviors conform to convenient stereotypes. Moreover, there are, as yet, no simple magic solutions whereby harmful behaviors may be prevented. Human behaviour is as varied and confusing as its attendant problems and negative consequences abound.

Constitutional or biological theories are related to biological predispositions to use or to misuse drugs or with the physical effects of their use. For example, animal research has indicated the existence of genetic predispositions to use drugs or to become dependent upon them. There is also some evidence in humans indicating that some people are predisposed to develop such problems as liver disease, alcohol dependence or certain types of cancers. It has been suggested that specific individuals, due to biological or psychological traits, are particularly attracted to stimulant, depressant or hallucinogenic drugs. Some people like particular drug effects. Such theories need to be considered in relation to a host of other individual factors, as well as social and cultural factors. If alcohol problems run in families, this could be for social as well as biological reasons (Goodwin 1976; Partanen, Bruun and Markkanen 1966; Kiianmaa, Tabakoff and Saito 1989; Kozlowski 1991).

A considerable amount of work has been conducted to identify an "addictive personality". The resulting evidence is contradictory. Many of these results stem from studies which have compared those who use alcohol or illicit drugs in a problematic way with "control groups" of different types. Often the latter have been chosen from rather unusual groups of people. These include those in penal institutions and clinic patients. Some studies have suggested that problem drinkers or problem drug users do differ from controls in relation to psychological characteristics such as neuroticism, hostility or extraversion. Even so, no unique "alcohol-dependent" or "drug-dependent" personality has been delineated (Fazey 1977; Plant 1981).

Some of those with serious alcohol or other drug problems have serious psychological disorders. It is often extremely difficult to tell whether these disorders are a cause or a result of the alcohol or drug use. Sometimes an alcohol or a drug problem appears to be at least partly caused by a secondary psychological condition. Studies of institutionalized problem drinkers and problem drug users vary considerably in their findings, with differing levels of association between psychoactive drug problems and psychological ill health (e.g. Kraft 1970; Barnes and Noble 1972; Lane 1976; Silver 1977).

Many theories have been propounded which attempt to relate drug use or misuse to the wider context in which such behaviors take place. A huge body of literature has examined social and cultural factors such as socio-economic status, poverty, and truancy, delinquency and family backgrounds. Some studies have sought to identify factors which are linked with drug use in the general population. Others have attempted to distinguish factors associated with atypical or harmful forms of drug use. As noted above, there is a considerable body of evidence that institutionalized problem drinkers and other problem drug users do exhibit high rates of other "problem" characteristics.

Patterns of drug use and misuse often vary in relation to socio-economic status. Different sub-groups in society have characteristic fashions in behaviour and this includes the use of legal or illicit drugs. In spite of this, both drug use and drug problems occur at all socio-economic levels. They are not the prerogative of the socially disadvantaged or those in extreme poverty. Even so, some forms of drug use and misuse are associated with social deprivation. Set against this, plenty of affluent people in high status occupations also misuse legal and illicit drugs (Stimson 1981; Royal College of Psychiatrists 1986; MacGregor 1989).

Studies of the use of drugs by young people repeatedly emphasize the importance of peer pressure in encouraging and maintaining drug use. Younger children, though usually much influenced by parents and other relatives, are also often subject to peer group influences. The latter become stronger with age and, by the teenage years, typically peer pressure from friends overtakes family influence in relation to styles of alcohol, cigarette and illicit drug use. Societies have "establishment" or "conventional" orientations towards issues such as drugs and sex. Typically these promote abstinence or moderation. Youthful peer group pressures may condone and foster very different fashions (Davies and Stacey 1972; Plant 1975; Bagnall 1991c).

It has been noted above that stressful life events have been linked with alcohol and drug problems. Considerable evidence also connects such problems with familial disturbance, such as separation from one or both parents, "broken homes" and parental drug abuse. There is also evidence indicating that if parents are strict non-drinkers this, like parental heavy drinking, fails to provide a model of moderate alcohol use for children to follow. Many clinical studies have noted that those with alcohol and drug problems do report backgrounds of severe family disturbance. Such backgrounds are, it should be noted, not unique to those with substance-related problems. Moreover, it is certainly not the case that all of those with alcohol or drug problems come from unduly troubled or dysfunctional families (e.g. Woodside 1973; Judson 1973; Blumberg 1981; Orford and Harwin 1982).

There is no doubt that the price and availability of both legal and illicit drugs are important influences on patterns of use and misuse. A major determinant of alcohol and tobacco consumption is the price of these products in relation to disposable incomes. Fluctuations in legal and illicit drug consumption reflect a variety of factors. These include attitudes to the drugs in question and social support for such drug use. Clearly, availability reflects consumer preferences. Even so, consumer preferences and consumption levels are, in turn, also influenced by price and availability (Plant, Grant and Williams 1981; Sales et al. 1989).

The list of theories put forward to explain legal and illicit drug use and misuse is almost endless. They include historical, economic, political and sociological theories. Most, if not all, of these theories are consistent with at least some examples of drug use. Nevertheless, the complexities and variety of drug-taking behaviour cannot be adequately explained by any single theory. It has, for example, even been suggested that there is a basic human need to experience altered states of consciousness. This may be so, but such states need not be attained through drug use. Music or meditation, for example, may produce much the same effects.