Medical Review Officer interpretation of laboratory results is an important component of drug testing programs. The clinical evaluation of laboratory results to assess the possibility of appropriate medical use of a drug is a task with many different facets, depending on the drug class considered. This intercession prevents the reporting of positive results unless it is apparent that drugs were used illicitly. In addition to the commonly encountered prescribed drugs that yield positive drug testing results, other sources of positive results must be considered. This review describes a series of compounds referred to as “precursor” drugs that are metabolized by the body to amphetamine and/or methamphetamine. These compounds lead to positive results for amphetamines even though neither amphetamine nor methamphetamine were used, a possibility that must be considered in the review of laboratory results. Description of the drugs, their clinical indications, and results seen following administration are provided. This information allows for the informed evaluation of results with regard to the potential involvement of these drugs.