Drug Testing False Positives Facts

If scheduled for a drug test for employment or sports eligibility, there are a few drug test false positives facts that you should know. Drug screenings are commonplace in everyday life, from pre-employment physicals and random workplace testing to drug screenings for high school and college sports eligibility—with a positive result often leading to a firing or ineligibility. What if that positive result were a “false positive”? By considering a few facts as you prepare for your next drug screening, you may avoid a dreaded false positive.

What is a false positive? Drug screenings analyze a body sample, such as hair, urine or blood, for the presence of known chemical substances—generally illegal drugs. Most tests seek out commonly abused drugs, such as marijuana, PCP, opiates, cocaine, and amphetamines. A false positive occurs when a tested individual shows a positive result for a substance when, in fact, an illegal substance was not used.

Why do false positives occur on drug tests? Drug screenings detect illegal chemical substances by their chemical structure. There are; however, a number of legal, over the counter medications and herbal remedies that have similar chemical structures to those banned. Unfortunately, the tests typically used for screenings lack the sensitivity to distinguish beyond the basic structures of the legal vs. the illegal—meaning that a person taking certain over the counter cold medications may return a positive result for an illegal drug because the test is not looking beyond the basic structure.

What are some common legal or over the counter medications that produce false positives on drug tests? Dextromethorphan, a common ingredient in over the counter cough and cold medicines, triggers false positives for PCP or Opiates. The common anti-inflammatory pain medication, Advil®, creates a positive for amphetamines in certain screenings. Prescription medications are not immune either—some penicillin medications, such as Amoxicillin, can yield positive cocaine results on drug tests. 

What can you do to avoid drug test false positives? Be sure to inform the test giver of any other prescription medications, over the counter medications, supplements or herbal remedies taken prior to testing. If you have provided a list of medications and supplements prior to testing, the testing facility will often perform additional testing to determine the exact substance generating the positive flag–but, if not, it will be easier for you to dispute a false positive. Keep a copy of any paperwork submitted during your testing, as that will be your best evidence of potential medications causing your false positive results.

What should you do if you receive a false positive on a drug screening? Speak up immediately so that additional testing may be done on the original sample or so that a second sample may be taken. Specific testing, such as that done by a gas chromatograph mass spectrometer, has the ability to distinguish the exact substance in question. This type of testing is not initially performed because of cost—but, is often a follow-up option for those facing serious consequences such as a job loss or jail time.

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