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Abstract
While individual genetic differences contribute to the development of substance dependence, genetic factors are considered one contributor to the complex interplay of physiological, social, cultural and personal factors that are involved.The classical (and popular) view of human genetics is one in which genetic mutation is the direct and usually only cause of a particular illness, for example, the single gene – or Mendelian – disorders such as Huntington’s disease.Single gene diseases are caused by specific mutated gene and the mutation is both necessary and sufficient to cause the illness. Unlike single gene disorders, which are rare and might affect 1 in 10000 people, complex disorders such as substance dependence,are common in the population, often affecting 1 in 100 or more people. Complex disorders are clearly not caused by genes alone, but by the interaction between genes and the environment thus exposure to psychoactive substances could have a much greater effect on somebody who carries a genetic vulnerability to substance dependence than on someone who does not.