Drugs are chemical substances that can change how your body and mind work. A drug test looks for signs of illegal drugs or certain prescription and/or over-the-counter (OTC) medicines that can be misused. The test is usually done with a sample of your urine (pee). Less commonly, drug testing uses a sample of your blood, saliva (spit), hair, sweat, fingernails, or breath.

Source: MedlinePlus, U.S. National Library of Medicine