Drug-checking services (DCS) provide people who use drugs (PWUD) the opportunity to have their substances tested before consumption. Though some suggest they may have adverse consequences, DCS have been introduced as a harm reduction (HR) strategy. A systematized review of the literature regarding drug checking (DC) methods and testing locations, advantages and disadvantages, and legal frameworks with an emphasis on HR was conducted referencing PRISMA guidelines. The primary search of PsychInfo, PubMed, Medline, CINHAL, CORE, and Web of Science was conducted between the 4 and 10 of September 2020, and 51 literature pieces were included in the final article. Most of the literature focuses on the benefits of currently available DCS. The services identified varied significantly in terms of testing methods, location of operation, primary goal, and the surrounding legal framework. The results suggest using multiple drug checking methods to be most beneficial. Further, DCS and the personalized interventions they provide can positively influence behavior change, minimize harm, and reduce mortality. DCS are a viable public health intervention that requires cross-sector support beyond the legal frameworks and testing methods. Services will need to be tailored to meet the needs of their chosen setting, local drug market, and target audience.