Different addictive substances affect the human body in a various way and cause different sorts of dependence: either mental, or physical, or both. Nowadays the list of psychoactive drugs accounts for more than a thousand items and many of them have a mixed effect, so they tend to be classified not by their chemical structure, but by the effect they have on a person. Most experts today adhere to the following drug classification: 1) central nervous system depressants. By the clinical effect they are narcotic analgesics that cause euphoria and at the same time tranquillization. This category includes opium, its derivatives - heroin, morphine, codeine, and synthetic analogues - methadone, tramadol, promedol, fentanyl. Hypnotics like barbiturates are also referred to the group of depressant drugs; 2) central nervous system stimulants. These are substances that have a euphoric effect and simultaneously accelerate the activity of the central nervous system: ephedrine, amphetamines, ecstasy, MDA, cocaine and its variations - crack cocaine, speedball; 3) hallucinogens - drugs that evoke euphoria and hallucinations. This group is comprised of so-called deliriants, i.e. volatile chemicals (glues, solvents, lacquers and other inhalants) and psychedelics, that can be subdivided into minor (marijuana, hashish, nutmeg, banana skin, etc.) and major ones (LSD, psilocin and psilocybin, mescaline, and others.).