The multiple application of immunoassay technology as the «initial test» to screen for drug abuse in various biological fluids and forensic matrices is well established and regularly practiced. Immunoassay methods refer to extremely convenient and quick analytical systems that rely on specific antigen antibody reactions for drug monitoring analysis. The evolution of development and commercialization of these technologies have significantly contributed to the overall efforts in deterring and detecting the abuse of illicit substances and the misuse of various prescription medications. Generally speaking, immunoassays serve as an economic and efficient screening tool to eliminate negative specimens from further analysis and to identify the class of drugs that requires the second confirmatory step.The present article provides an overview of the fundamental principles of immunoassay methods, their general characteristics, specific limitations, various and recognized advantages and disadvantages. It describes clearly the most commonly used immunoassays for drug abuse screening, such as EMIT, RIA, FPIA and CEDIA
