What are the Different Causes of a False Positive Drug Test?

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  • Written By: wiseGEEK Writer
  • Edited By: O. Wallace
  • Last Modified Date: 17 November 2019
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There are numerous substances that can cause a false positive drug test result. Many of these are common medications that a number of people use while other substances are herbal treatments, foods or supplements that may cause a drug test to read improperly. Additional causes include testing or labeling errors or certain medical conditions.

As stated, one reason for a false positive drug test is laboratory error. Either the laboratory did not properly perform the test, or a labeling error occurred. Some labs are certified as drug testing labs and others are not, and some employers or other agencies performing drug tests don’t necessarily use a certified lab. If people can rule out all other potential causes of positive testing, they might be able to retake a test or redo it at a different lab, though this option isn’t available to everyone.

Undoubtedly, one of the main causes of a false positive drug test is using other medications. Some of those most indicated in false positive readings are over the counter cough and cold syrups, decongestants, and over the counter nasal sprays. Some prescription medicines used for pain relief or serious cough actually contain drugs like codeine, hydrocodone or oxycodone, and these may cause a true positive on very extensive tests or false positives on limited tests.


Antidepressants like Zoloft® or Wellbutrin® and antibiotics like Levaquin® and amoxicillin may cause false positive readings, and again, true positive readings could occur if people take drugs like tricyclic antidepressants, barbiturates, amphetamines, or benzodiazepines. These medications are legally prescribed for conditions like depression, anxiety, sleep problems, seizures, or attention deficit hyperactivity disorder. Similarly, some asthma medicines create inaccurate readings. A simple pain reliever like naproxen sodium may also read as drug use.

Herbal treatments and supplements may be reason for a false positive drug test. Several vitamin B supplements, anything that contains or is made from hemp, and substances like valerian or ephedra can affect drug testing. There are also foods such as the poppy seed, and any foods containing the supplements or natural substances above that might be an issue.

Some forms of liver and kidney disease have been linked to false positives. Those not taking any substances listed above, or eating any of the potential foods that can cause problems might want testing from their doctors to determine if an underlying medical condition exists. This could be used to challenge results.

In all, there’s an overwhelming list of false positive drug test causes. People awaiting drugs tests should keep a list of all medications/supplements they take and be ready to present information on legal prescriptions required for medical conditions.


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Post 3

I'm a diesel engine mechanic and my hair follicles test came back positive for methamphetamine and amphetamines and I don't take drugs. Please, can someone tell me how it was possible?

Post 1

Can you answer on the flight attendant that has been turning up positive. She is battling custody and discontinue drinking. What can cause the elevation on the test?

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