Recent years have seen a steady growth in the availability and consumption of novel psychoactive substances (NPS) across the world. NPS are sold as legal, cheap and non-detectable substitutes for controlled drugs of abuse. The consumers are not normally provided with certain information on the composition of the product, or the recommended dosing and possible side effects. According to the EMCDDA, since 2009, tens of new compounds belonging to six major groups of NPS are introduced into the market each year. These major categories include psychostimulants, synthetic cannabimimetics, psychedelic compounds, dissociatives, synthetic opioids and benzodiazepine analogues. The number of compounds belonging to the two most popular groups, psychostimulatory cathinones and synthetic cannabimimetics, makes up to two-thirds of the total number of NPS. The great majority of NPS are synthetic compounds, and some of these were initially designed as potential medicines or pharmacological tools. NPS exert their actions by various pharmacological mechanisms such as the enhancement of central monoaminergic neurotransmission for psychostimulants, activation of cannabinoid receptors by synthetic cannabimimetics, activation of serotonin receptors by psychedelics, antagonism for NMDA receptors for dissociatives, and activation of μ-opioid and GABAA receptors by synthetic opioids and benzodiazepines, respectively. NPS can produce a wide spectrum of life-endangering side effects. Some of these actions are specific to a certain compound or group of compounds, while some can be produced by drugs from different classes of NPS. In general, NPS may impair cognitive functions, exacerbate or trigger mental disorders and cause severe neurological and cardiovascular symptoms. Significantly, there are specific antidotes for only two groups of NPS, opioids and benzodiazepines, and treatment of acute NPS intoxication is therefore usually symptomatic.
