False Positive Drug Tests: Understanding Causes & Minimizing Errors for Drug-Free Workplaces

False Positive Drug Tests

False Positive Drug Tests: Understanding Causes & Minimizing Errors for Drug-Free Workplaces

This article highlights the importance of drug-free workplaces, delving into the causes of false positive drug tests and offering error-reduction strategies.

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UPDATED: 12/8/2023

Maintaining drug-free workplaces is crucial for the safety, productivity, and well-being of employees. Drug testing plays a vital role in ensuring a drug-free environment, but false positive results can occasionally create confusion and in interpretation of results. In this blog post, we will explore the causes of false positive drug tests, discuss strategies to minimize errors and introduce DrugTestKitUSA as a trusted supplier of reliable drug test kits.

Understanding False Positive and Negative Drug Tests

A false positive drug test occurs when a test indicates the presence of a drug in a person’s system, even though they have not consumed that substance. False-negative results occur when a medication or metabolite is present at such low concentrations that it is not identified. In some cases, contaminants can also impair the immunoassay’s capacity to identify the presence of medicines.

False positives can be caused by various factors, including cross-reactivity with other medications or substances, food items, laboratory errors, or inadequate sample collection and handling.

Common Causes of False Positives


  1. Antidepressants: Certain antidepressant medications, such as trazodone and bupropion, may lead to false positive results for amphetamines.
  2. Antibiotics: Antibiotics such as, Fluoroquinolones, especially Levofloxacin , can give false positive tests for buprenorphine and morphine/opiates.
  3. Pain Medications: Over-the-counter nonsteroidal anti-inflammatory pain medication such as ibuprofen or naproxen can give false-positive results for barbiturates and cannabinoids.
  4. Antihistamines: Common antihistamines such as diphenhydramine (Benadryl) may produce false positive results for opiates or PCP (phencyclidine).
  5. Medications for Colds and Allergies: Over-the-Counter (OTC) medications such as phenylephrine, phenylpropanolamine, pseudoephedrine and nonprescription nasal antihistamine and decongestant inhalation meds can result in false positive results for amphetamines.
  6. Other Medications: Additional types of medications can cross-react with drug tests and produce a false-positive result in immunoassays.  Drug test package inserts usually offer a partial list of drugs that cross-react.  Confirmation laboratory testing is an important second step after screening with an immunoassay test.
Learn more about the exact type of medication and which drugs they may cause positive results from Drugs.com.

Foods and Drinks:

  1. Poppy Seeds: According to a study published on 28th Feb 2023 by the University of Florida Health, Consuming foods that contain poppy seeds can lead to false positive results for opioids. Although, this occurs less frequently with the higher SAMHSA cutoff of 2000ng/ml.
  2. Hemp and CBD (Cannabidiol) Products: Some hemp and CBD products may contain trace amounts of THC, the psychoactive component of marijuana. Ingesting these products could potentially result in a false positive for THC.

Activities and Environmental Factors:

  1. Second-hand Smoke: Being exposed to second-hand marijuana smoke in an unventilated area may lead to positive results for THC. However, the concentration of THC in second-hand smoke is typically much lower than in active marijuana use.
  2. Passive Exposure: Being in close proximity to individuals using certain drugs, such as cocaine or methamphetamine, may cause false positive results due to passive exposure.
  3. Environmental Contamination: Contaminated surfaces or objects that have come into contact with drugs can potentially lead to false positive results if proper precautions are not taken during sample collection and handling.

False Positive Drug Tests

It’s important to note that these substances and activities may not always produce false positives or false negatives in drug tests, but they have the potential to do so. If an individual tests positive, it’s crucial to consider possible explanations, such as legitimate medication use or exposure to substances in the environment. A quantitative test using nonimmunologic techniques such as gas chromatography, mass spectroscopy, or high-performance liquid chromatography should be used for confirmation.  A positive immunologic test result should be considered a “presumed positive” or “non-negative result”.  Positive results should be confirmed in the lab.  Often, as part of a drug testing program, an independent specialist, a Medical Review Officer (MRO), reviews the results of screening and confirmatory testing.   They will review the employees’ current medications and medical conditions, identifying substances that may trigger false positives.  This helps ensure accurate interpretation of test results.

The Importance of Drug Testing

Implementing effective drug testing programs is crucial for promoting workplace safety, reducing accidents, and ensuring a productive and healthy environment. Drug testing acts as a deterrent, discouraging employees from using illicit substances and creating a safer working environment for all.

To achieve accurate and reliable drug test results, businesses can rely on DrugTestKitUSA as a trusted supplier. DTKUSA offers a wide range of drug testing kits, including urine and saliva tests, ensuring high-quality products that provide accurate results.


False positive drug tests can pose challenges in maintaining drug-free workplaces. Understanding the causes of false positives and implementing strategies to minimize errors are crucial steps in ensuring accurate and reliable drug test results. Maintaining a drug-free workplace is not just about compliance; it is about prioritizing the safety, well-being, and productivity of employees. By partnering with DrugTestKitUSA and implementing comprehensive drug testing programs, businesses can contribute to creating a safer and healthier work environment.

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