What Urine Drug Testing Can and Cannot Measure
"Urine drug tests, which are the least expensive and most frequently used form of drug test, can generally detect marijuana use within the past week; cocaine, heroin and other 'hard' drugs used within the past two days; and alcohol use within the past several hours (though alcohol is not often included in drug screens). Drug tests cannot measure frequency of use, nor do they indicate the severity of impairment or whether an individual has a substance use disorder that requires treatment. In addition, without medical review and confirmation testing on initial positive results, 20 urine screens also cannot distinguish between the illicit use of street drugs and the legitimate use of certain prescription and over-the-counter drugs. For instance, a drug test cannot distinguish between prescribed Tylenol with codeine and illicit opiates. Improper testing procedures and mishandling of samples can also produce inaccurate results."
"ASPE Issue Brief: Drug Testing Welfare Recipients: Recent Proposals and Continuing Controversies," Dept. of Health and Human Services Office of the Assistant Secretary for Planning and Evaluation (Washington, DC: October 2011), p. 4.