Investigators at the University of Kansas Medical Center conclude: "Immunoassays, which use antibodies to detect the presence of specific drugs or metabolites, are the most common method for the initial screening process. … However, these assays are not perfect. False positive results of immunoassays can lead to serious medical or socials consequences if the results are not confirmed by secondary analysis. … Also, urine drug screens do not provide information regarding the length of time since last [drug] ingestion, overall duration of [drug] abuse, or state of intoxication."

Authors report that various prescription and over-the-counter medications may yield false positive drug test results on immunoassay tests, though these results are primarily limited to amphetamines, opioids, and phencyclidine (PCP).