In drug and stimulant studies it is very important to keep the preanalytical phase controlled by the laboratory specialist. In this process, it would be most appropriate to cooperate with the clinical unit requesting the analysis and to plan the appropriate conditions and workflows together. The preanalytical phase includes; determining the appropriate sample, configuring the test panel correctly, regulating the data processing system, identification of samples, control of the physical arrangements for taking samples under surveillance, taking precautions to prevent adulteration, obtaining patient consent, creating prosedüres to safe transfer and admission of samples, safe storage, defining sample suitability before analysis.