Illegal drugs, or “narcotics,” are psychoactive substances whose use and possession are prohibited. These prohibited psychoactive substances are included on a list of “narcotics” established by the February 22, 1990, decree of the Ministry of Health and regularly updated. The list of narcotics is available on the website of the French National Agency for Medicines and Health Products Safety (ANSM).
The purpose of classifying a substance as a narcotic is to restrict its use to medical and scientific purposes only and to regulate its use.

Illicit drugs encompass a wide range of substances that vary greatly in terms of composition, form, effects, and health risks. They can be organized into different classes based on their primary effects. There are several classifications of drugs (both licit and illicit). The classification by Yves Pelicier and Jean Thuillier (1991) distinguishes three groups: depressants, stimulants, and disruptors. Each of these classes has specific effects and risks.

• Depressants, such as heroin and other opioids, work by slowing down the functioning of the central nervous system: they slow down both mental and physical functions, lower the level of alertness, and relieve pain.

• Stimulants, such as cocaine, MDMA/ecstasy, or amphetamines, work in the opposite way: they accelerate the functioning of the central nervous system, stimulate mental and physical functions, increase alertness and vigilance, and reduce feelings of hunger and fatigue.

• The class of disruptors is more complex to characterize, as it encompasses a more heterogeneous group of substances. Substances that are neither pure depressants nor pure stimulants, such as cannabis, fall into this category. Hallucinogenic substances, such as LSD, are also classified in this category. These substances disrupt mental functions, alter brain activity and cognitive functions, and distort sensory perceptions (visual and auditory hallucinations, distorted bodily sensations). New psychoactive substances (NPS) could also be included in this category since they often have combined effects.

Since the mid-2000s, new psychoactive substances (NPS) have emerged, most often designed to circumvent drug control laws. These substances are available online under various names and are not necessarily detectable in surveys of the general population. New psychoactive substances refer to a highly diverse range of substances belonging to the three classes described above, which mimic the effects of various illicit drugs (ecstasy, amphetamines, cocaine, cannabis, heroin, etc.). Their molecular structures are similar to those of these drugs without being exactly identical. This allows them, at least in the short term, to circumvent drug laws. In France, the main NPS are synthetic cannabinoids (which mimic the effects of cannabis), cathinones (which mimic the effects of cocaine and MDMA), and phenethylamine derivatives (which mimic MDMA and amphetamine).