SAMHSA (Substance Abuse and Mental Health Services Administration), a federal agency, regulates federal workplace drug testing and requires testing for amphetamines, cocaine, cannabinoid (marijuana), opioids, and phencyclidine (PCP). In addition to these abused drugs, many private employers also test for benzodiazepines, barbiturates, methadone, etc. Some employers also test for methaqualone and glutethimide. Usually, immunoassays approved by the Federal Drug Administration (FDA) are used for screening the presence of these drugs in the urine. If any test is positive, then the presumptive positive drug is confirmed by a second analytical technique, preferably by gas chromatography/mass spectrometry (GC/MS) or, more recently, using liquid chromatography combined with tandem mass spectrometry (LC-MS/MS). Immunoassays suffer from cross-reactivity with other drugs or related substances and may show false-positive results. GC/MS or LC-MS/MS offers a more sophisticated analytical method and is considered as the gold standard for drug confirmation. Confirmation is also required for workplace drug testing.