Background and Objective: In the last decade, the phenomenon of using new psychoactive substances (NPS), called designer drugs, has been on rise. Though their production and marketing in Poland is prohibited, reports of the Supreme Audit Office noted that young people are increasingly reaching for new intoxication agents in the form of designer drugs. There is a significant increase in the number of patients with NPS abuse admitted to the emergency departments. As NPS cannot be detected by standard tests for the presence of psychoactive substances, it is difficult to choose the appropriate therapeutic intervention. Therefore, the aim of the present study was to evaluate the patient characteristics in the population of adults and children suspected of using NPS and formulate the protocol for diagnosis and treatment. Materials and Method: The paper is based on a retrospective analysis of medical records of hospitalized patients in the Clinical Emergency Department of The Regional Specialist Hospital in Olsztyn (SKOR WSS, emergency department (ED)) and the Pediatric Emergency Department of the Provincial Specialist Children′s Hospital in Olsztyn (SORD WSSD, pediatric emergency department (PED)) between years 2013 to 2018. The patient records related to their general symptoms at admission, mental state and laboratory diagnostic tests were evaluated. Results: The majority of patients hospitalized due to the suspected use of NPS were adolescents in 2013–2016 and a reversal of this trend was observed in 2017–2018 when number of adults admitted to the emergency department (ED) due to NPS use was higher. The NPS abuse was significantly higher among male patients, alcoholics, people using other psychoactive substances, patients suffering from mental disorders and teenagers in difficult socio-economic family situations. Whereas, the most common symptoms among pediatric patients were co-ordination disorder and aggression, in adults mainly tachycardia and aggression was observed. The laboratory tests in significant number of adult patients showed leukocytosis and ketonuria. Conclusions: In the present study, no unambiguous toxidrome or biochemical pattern characteristic for using NPS was observed. However, evaluation of blood morphology, coagulation parameters, liver and kidney function can be helpful in the diagnostic and therapeutic process. Symptomatic treatment of patients, fluid therapy and sedation was sufficient in most cases to resolve the patient symptoms in 48 h.