The occurrence of psychotropic substances (PSs) in the air is known since long time. Recently, attention was paid to illicit PS, with most investigations undertaken in Italy and Spain. In general, collection of illicit substances was performed through aspirating airborne particulates onto filters; afterwards, gas chromatography or high-performance liquid chromatography coupled with mass spectrometry were applied for the PS evaluation. Over twenty substances could be characterized simultaneously. Cocaine concentrations up to 17 ng m− 3 were observed in Latin America, while this substance was absent (< 0.003 ng m− 3) in Algiers (Algeria) and Pančevo (Serbia). Cannabinoids (comprising the psycho-active principle Δ9-tetrahydrocannabinol [THC]) were high in the winter and very low in the summer (up to 6 ng m− 3 and < 0.1 ng m− 3, respectively). Many other substances (e.g., heroin, ephedrine and drug by-products) occurred less frequently and at lesser extents (< 20 pg m− 3). In Rome (Italy), investigations were carried out in interiors of dwellings, schools, an office and a coffee bar, all sites resulting affected by drugs. Besides, solid phase microextraction methods were applied to detect ketamine and methamphetamine in interiors. The PS concentrations depended on substance, physical–chemical contour, and internal or external type of locations. Air monitoring allows detecting the drug consumption or preparation, because illicit substances prevail in sites frequented by abusers.