Drug-checking services provide individuals who use drugs with information on the chemical content of their drugs as well as advice and, sometimes, counselling or brief interventions. Service priorities vary and may include information collection, harm reduction and early warning. The analytical techniques used also vary: from sophisticated technology that is able to provide information on strength and content of a wide variety of substances, such as high-performance liquid chromatography and Fourier transform infrared spectroscopy, to methods that simply show the presence or absence of a particular drug, such as thin-layer chromatography and reagent test kits.