Review: False-Positive Interferences of Common Urine Drug Screen Immunoassays

Emily C. Lennert

Category: Chemistry

Keywords: drug test, drug screen, urine test, urine screen, false positive, interferences

Article to be reviewed:

  1. Saitman, A.; Park, H.-D.; Fitzgerald, R. L. “False-Positive Interferences of Common Urine Drug Screen Immunoassays: A Review.” Journal of Analytical Toxicology 2014, 38 (7), 387–396.

Disclaimer: The opinions expressed in this review are an interpretation of the research presented in the article. These opinions are those of the summation author and do not necessarily represent the position of the University of Central Florida or of the authors of the original article.


The review article provides a summation of some false positive interferences that have been reported in urine drug screens. Urine drug screens are conducted using immunoassays. An immunoassay is a simple, dipstick style test, which can be conducted in a matter of minutes. These immunoassays can test for illicit drugs and drugs of abuse, such as amphetamines, benzodiazepines, cannabinoids, opiates, and more. These drug screens are intended as preliminary tests, and positive results should be sent for confirmatory analysis at a toxicology laboratory. Confirmatory analysis is most often performed by gas chromatography-mass spectrometry (GC-MS.) In this study, a false positive is the indication of an illicit drug or drug of abuse when the drug is not actually present. This study reported medication interferences that lead to false positives. This summary will focus on the more common medications that caused the false positive results.

Instances of false positive identification of amphetamines were reported for some individuals using an energy supplement called dimethylamylamine (DMAA). False positives were also reported for individuals taking bupropion, a common smoking cessation medication as well as antidepressant. The psychiatric medications promethazine and chlorpromazine were also reported to cause false positive indications of amphetamine presence. Trazodone, a common antidepressant, was reported to have caused false positive indications for methylenedioxymethamphetamine (MDMA).

False positives for benzodiazepines were reported for only two medications. Efavirenz, an HIV treatment, and Sertraline, a common antidepressant, were reported to cause false positive indications for benzodiazepines.

False positives for cannabinoids, such as THC, were also reported. Efavirenz was also found to produce false positive indications for cannabinoids. Additionally, the common over-the-counter anti-inflammatory medications ibuprofen and naproxen were reported to cause false positive indications. Niflumic acid, a muscle and joint pain reliever, was also reported to cause these false positives.

False positives for phencyclidine, PCP, were reported for venlafaxine, an antidepressant, and lamotrigene, an anticonvulsant and mood stabilizer. Sertraline, a common antidepressant, reportedly resulted in false positive identification of lysergic acid diethylamide (LSD).

False positives for opiates were also reported in this study, however the interfering medications were not common medications. These medications included morphine, methadone, and codeine, among others.

Scientific Highlights:

  • Common medications were found to cause false positive identifications of illicit drugs or drugs of abuse in urine screens by immunoassays.
  • GC-MS confirmation is necessary to make a positive identification of the presence of a drug in a urine sample.
  • Immunoassays alone are not reliable and should be considered only a preliminary test, sine the tests are prone to false positives.

Relevance: This study, though conducted with the medical field in mind, underscores the importance of confirmatory testing of positive drug results in urine samples by GC-MS. This is applicable to the forensic science and legal community. Common legal medications may yield false positives for illicit drugs, and it is important that the presence of an illicit drug is confirmed to avoid legal punishment of innocent persons.

Potential conclusions:

  • Urine drug screenings may be prone to false positive identification of illicit drugs or drugs of abuse.
  • Many false positives may be caused by common medication, taken for legitimate medical reasons.
  • Urine drug immunoassays alone do not provide reliable evidence, and must be followed by confirmatory testing, such as by GC-MS.