The Viennese addiction prevention project checkit! provides counseling based on on-site chemical analysis of recreational drugs at parties, festivals and in clubs. This combined approach is often referred to as integrated drug checking (IDC). Lately the European drug market has become more and more complex, with the number of new psychoactive substances (NPS) available on the drug market increasing steadily. In addition to this, the concentration of active ingredients of some recreational drugs has rapidly risen in recent years. For comprehensive harm and risk reduction measures, the identity and the quantitative composition of psychoactive substances need to be determined on the spot. In order to meet the high demands of IDC, checkit! operates a mobile UHPLC-MS (Ultra High Performance Liquid Chromatography - Mass Spectrometry) system for fast analysis. In addition, the checkit! lab recently introduced a direct mass spectrometric method (MALDI-IT-MS) to detect even low doses of highly potent substances, i.e. synthetic opioids and cannabinoids that appeared in this specific setting. Importantly, the analysis-results are communicated individually by professional counselors together with substance information in an anonymous counseling session. The accurate and quick quantitative and qualitative analysis of psychoactive substances thus forms the core for the specific addiction prevention intervention.