g) The plants were used as nutritional sources providing vitamins, minerals, and proteins rather than recreational psychotropic substances inducing inebriation. Due to limited resources within ancient environments, mammalian species most probably sought out CNS neurotransmitter (NT) substitutes in the form of psychotropic allelochemicals, because nutrient NT-precursors were not largely available in the forms of food. Therefore, drugs became food sources to prevent decreased fitness from starvation and death. It is believed that early hominid species evolved in conjunction with the psychotropic flora due to constant exposure with one another. This may be what eventually allowed the above civilizations to use the flora as nutritional substances, therefore increasing both their fitness and viability.

In the same line, psychotropic drugs could have evolved to present allelochemical reactivity in order to deal with threats from herbivores and pathogenic invasions, as if they were an imitation of mammalian neurotransmitter system, that act like competitive binders, obstructing normal functioning of central nervous system (34-35). This ideas reinforce that where the evolution of mammalian brains and psychotropic drugs where co-dependent, that is to say that existed an ecological interaction and influenced one another in terms of evolution (34). One set of examples to reinforce this hypothesis, but maybe the most striking one is that in the mammalian CNS we found opioid receptors, but the truth is that the body do not provide any natural opioid substance by himself (so that could be pretty more logical that some environmental effect forced the mammalian organism to develop receptors to exogenous opioids) (35).

Most of the times, the way to describe the beginnings of ancient drug utilization is based on the artifacts that remains from older eras and is target of the study of the so called archeobotany or archaeoethnobotany(36).

For example, considering hallucinogenic drugs, hallucinogenic plants are most of the times considered as the principal source of psychoactive drugs (37). The authors state that these drugs must be used to reach deep altered states of consciousness. It’s also stated that several investigators believe that this was particularly accurate during the Tiwanaku empire expansion, surrounding the era of 500-1000 A.D., along the Atacama Desert of Chile. In equal way, emphasize the roll that artifacts played in those conclusions, such as decorated snuffing tablets and tubes, as well as grave goods during this period (“until now the type of drugs consumed in this paraphernalia has been unclear”) (37).

About the archeological discovers in Shumla Cave number 5, Rio Grande, Texas, USA, and states that the identification of mescaline, in that sample, strengthens the evidence that native North Americans considered and used the psychotropic properties of peyote for at least 5700 years ago(38). Prior studies have shown that the utilization of psychotropic drugs in that region of North Mexican and South American border could be dated from 8500 BC (39).

There are several studies that stress a possible genetic factor in facilitation of drug use initiation like in nicotine (40), alcohol (41) and a plethora of drugs. For instance, in a study of two groups with more than one thousand female twins, monozygotic and dizygotic, were evaluated possible association of genetic influence on drug use(42). They found some evidences that genetic influences have a say to vulnerability to drug use, and each category of drugs, apart from hallucinogens, presents distinctive genetic influences. The genetic influence of vulnerability was superior for heroin than for other drugs (42). In other separated studies including samples of twins of both sexes, suggest a superior genetic weight in men for vulnerability to drug abuse/dependency reaching 60-80% of the genetic weight in the development of drug use and abuse (43-44).

Some authors presented a literature review on family and in two well known phases of drug addiction treatment and processes: engagement and treatment (45). According to the cited sources, the article highlights the necessity for addict patients to be treated along with their families (some authors suggest Familiar Therapy) so that adequate results could be expected. The importance of socio-cultural issues can influence institutional treatment and call attention for the necessity that treatment of addict’s patients and their families, as well as effective preventive action programs (45). These point gains considerable relevance since it is well known the dependence developed by intra-uterine via in pregnant mothers that continues the use and abuse of drug during pregnancy, with proved deleterious effects for her siblings (46). Some examples are the fetal alcohol syndrome (47), neonatal withdrawal syndrome(48), neonatal abstinence (49), effects of pre-natal exposure by cocaine, amphetamines and heroin (50-51), etc.

For example, in a recent study with 1836 subjects tried to “examine substance use and dependence among cocaine dependent subjects and their siblings compared to individuals recruited from the same neighbourhood and their siblings in order to better understand family and neighbourhood contributions to the development of dependence” (p. 14)(52). Cocaine dependent subjects came from treatment centres and community-based subjects were sample-matched to cocaine dependent cases, with one full sibling for each case and community-based subject. The results show a higher risk rate of cocaine and other substances use in siblings of cocaine users. Nevertheless, the authors conclude that Cocaine dependence is characterized by poly-substance use and dependence. Stressing that the prevalence of substance dependence in the community subjects was higher than reported for the general population, they state that cocaine dependent cases probably live in higher-risk communities, characterized by an elevated prevalence of substance dependence (52).

Although all data presented, many researchers and also a great part of social general opinion, support ideas from the Institute for Health and Social Policy, from USA, that suggest that the most important factors for the initiation and continuation of drug utilization are societal factors, that could include the tolerance for drug utilization - perceptions of negative social and health consequences of the use of these drugs - as well as the availability and the ways the drugs are set in the market (53). In our opinion, this type of hypothesis appears not to consider the possible inner predisposition for drug consumption, based on the well known vulnerability model. Generally speaking, the idea is that in drug abuse (whether in initiation or in chronic abuse) at least three major factors should be taken into consideration: the psycho emotional subject, the environment and the “genetic subject”. This could be considered as a Multifactorial Polygenic Heritage. Several studies strongly suggests this for alcohol dependence starting in animal (54), human first-degree relatives of alcoholics (55), adopted Childs from alcoholic and non-alcoholic biologic parents(56), monozygotic and dizygotic twins (57), siblings of alcoholics compared with nonalcoholics in terms of risk factor (58). The same hypothesis has been putted for other drugs although at a lower rate of published data. For the importance and clearness of ideas we transcribe here a part where this point is strongly approached (59):

If genetic factors are involved in drug abuse, what does this mean? First, we must realize that genes do not directly cause behavior.

No gene or set of genes, for example, will directly cause a person to become a drug abuser or to engage in drug-taking behavior.

Instead, genes are segments on chromosomes that code for the production of specific proteins (or serve to regulate the activities of other genes) that are important in the control of behavior. If a gene is absent, a protein that controls the development or function of a physiological system may not be produced. In certain cases, the impact may be obvious, as in the case of phenylketonuria, when failure of a gene to code for the enzyme responsible for metabolism of phenylalanine results in development of a severe form of mental retardation. In other cases, however, the impact of genes on behavior may be less obvious but just as real, as when genetic factors produce a tendency or predisposition to respond in a certain manner. Such is believed to be the influence of genes on a number of behavioral traits and disorders, including alcoholism and drug dependence. Thus, genes are not the sole determinant of alcoholism or drug dependence, but their presence (or absence) may increase the likelihood that a person will become alcoholic or drug dependent. Second, as the above statement indicates, genes do not act alone in determining whether a person will become alcoholic or drug dependent. Our experience in behavioral genetics suggests that both genetic and environmental factors will ultimately be implicated in the etiology of drug abuse. As with alcoholism, simple cause-and effect models will not be sufficient for explaining vulnerability. Rather, various combinations of biological and environmental factors are likely to be identified that function to attenuate or exacerbate an individual's likelihood for becoming drug dependent. Just because an individual has a genetic tendency for developing drug dependence does not mean he or she will necessarily develop the disorder. Whether the disorder develops will ultimately depend on environmental influences.

Certain types of environmental influences are believed to be necessary for a genetically vulnerable person to develop drug dependence. For example, one environmental influence that is essential to the development of the disorder is that an individual must initially engage in drug-taking behavior. Thus, while a person may be genetically loaded for drug dependence, if drugs are never used, that person will never run the risk of becoming drug dependent. The presence of other environmental factors in the development of drug dependence (e.g., drug availability, the manner in which a person uses drugs) is also suspected. These may include environmental influences that operate within the immediate milieu (e.g., family and peer influences) or more broadly (e.g., cultural factors). Third, genes may influence a person's tendency to develop drug dependence in many ways. Most people believe that genetic influences operate by producing an aberrant or idiosyncratic biological response to drugs. For example, genes may make some people more (or less) sensitive to a drug's effect, or they may produce a qualitatively different drug effect in some people than in others. While this may indeed be the case, it is important to recognize that there are mechanisms other than pharmacological mechanisms that may account for genetic effects. One nonpharmacological mechanism is that genes may determine personality characteristics that increase the probability of drug abuse. For example, a person may inherit a sociopathic personality that increases the likelihood of contact and experimentation with drugs.

Cultural factors may in part be genetically determined, which may increase the likelihood of drug use that will eventually lead to increased rates of drug dependence (59).

Of course we do not lose of sight the social impact of drug abuse, like the one, for example, related with crime. For instance, substance abuse is habitually found in violent offenders (60). He mentions data from DSM-IV (1994), “more than one-half of all murderers and their victims are believed to have been intoxicated with alcohol at the time of the murder.” (60)