In the present paper, major issues related to drug testing are discussed. For example, drug-testing techniques measure the presence of a drug or drugs but are not sophisticated enough to measure impairment from drug use. Moreover, it is difficult to determine the route of drug administration, quantity or frequency, as well as when the drug was taken, on the basis of the laboratory results. Selection of the drug to be tested should depend on the local availability of the drug, its abuse potential and clinical effects, as well as on the availability of analytical technology and expertise in testing and in interpreting laboratory results. The most sophisticated drug-testing approach is gas chromatography coupled with mass spectrometry (GC/MS), which is regarded as a "gold standard"; it is used in confirmatory testing. Typically, GC/MS is preceded by a rapid immunoassay method to eliminate the majority of the "negative" samples. Despite the existence of sophisticated drug-testing methods, it is still possible to obtain incorrect test results. Such results may be caused by the presence of interfering substances or adulteration of the urine sample. A number of techniques can be employed to reduce the likelihood of obtaining erroneous results and to detect adulterated urine samples. A "positive" drug finding can have a serious impact on the livelihood of an individual, therefore, persons conducting such tests should adhere to the strictest standards of laboratory performance. Only qualified and experienced individuals with proper laboratory equipment should perform these analyses. The standards of laboratory performance must meet local legal and forensic requirements. Access to patient samples and laboratory records must be restricted in order to prevent the tampering of samples and results. In order to maintain confidentiality, the results must be communicated only to the medical review officer. Chain-of-custody documents and all file so that they can be examined in case of a legal challenge. The laboratory must have a complete record on quality control. Finally, specific initial and confirmatory testing requirements should be met.