A scientific definition of the toxicomania, which will include its main chemical, pharmacological, physiopathological, psychotoxic characteristics and its medical-social implications, is hard to formulate. The World Health Organization (WHO), in the year 1952, based on a long study made by a group of experts which attended narcotics, elaborate the following definition: “Toxicomania is a state of periodical or chronic intoxication, harmful for the individual and for the society, caused by the repeated use of a drug (natural or artificial) of which characteristics are the following: 
- An invincible desire or a need to continue using the drug and to procure it by any means;
- A tendency to increase the dosage;
- An addiction of psychic order (psychological) and sometimes physical toward the effects of the drug”.
The notion of drug has a wider meaning and is not synonymous with the one of dope, even though in the Larousse dictionary it is defined this way: “the name given for dopes (cocaine, morphine); figurative: thing very bad to absorb”. In a wider meaning, the drug is any chemical substance that influences the living protoplasm. The dope is a substance that causes through repeated administration the specific phenomenon of pharmaco-addiction. The magazine “Sante du Monde” of the WHO determines that it must be considered a drug: “any substance (having or not legitimate medical applications) that makes the object of an abusive use in other purposes than medical”. Beside the specific actions over the central nervous system, over the psyche, for each group of drug addicts, it must be pointed out that all are accompanied by three phenomena: tolerance, pharmaco-addiction and the abstinence crisis.
Tolerance is a feeling that installs slowly and is explained through the reaction of adapting of the organism at the same dosage of drug administered repeatedly and as a consequence, the reaction of the organism diminishes at the same dosage of the.
The pharmaco-addiction is a particular psychic state and often physical which results from the interaction between the living organism and a drug (medicine) which trains specific behavior modifications-an imperative need to continue using the drug, from the desire to reproduce its physical effects (and psychic). An individual can be addicted to several drugs.
The pharmaco-addiction can be associated or not with the phenomenon of tolerance. The abstinence (the wean) represent a particular phenomenon, which appears generally after twelve-forty-eight hours from interrupting the administration of the drug and which causes for the toxicomaniac violent reactions: neuropsychological (nervousness, anxiety, insomnias), cardio-vascular disorders, until the state of collapse, such as at morphine addicts, muscular spasms, hyper-salivation, vomits, diarrhea. This state of crisis, which appears from the drug, is difficult to bear by the addict, which pushes him again toward the vice.
Varenne tries a classification of the toxicomanias, based on three criteria: physical addiction, tolerance and psycho-toxicity, emphasizing their harmlessness, in descending order viagra online.