The Truth About False Positives and Employment Drug Screens

Jim Akin

Employee drug screenings have been standard procedure for decades in many industries, but the nation’s ongoing crisis of opiate and opioid abuse make it a growing focus for employers and HR professionals across the country. Reports that workers are failing workplace drug tests at the highest rates in over a decade also have many companies revisiting and updating existing policies.

One study showed the positivity rate for methamphetamines climbed 64 percent between 2012 and 2016 in the general U.S. workforce.

With increased attention on testing policies comes a need for greater awareness of the strengths and weaknesses of testing procedures, including the potential for false-positive test results that can come with expansion of the type and number of drugs included in screening programs. False positive results are a manageable element of workplace drug-test programs.

Why Do Employee Drug Testing?

Reasons for implementing drug testing procedures vary by employer. Some regulated industries require testing of employees, especially those with jobs that impact public safety. But whether mandatory or discretionary, virtually all drug testing addresses one or more of the following concerns:

  • Safety. Employees under the influence of alcohol or drugs are at greater risk for industrial accidents, driving infractions and accidents, and other mishaps that endanger them and their coworkers.
  • Liability. Intoxicated workers who come into contact with clients, customers, and the general public expose their employers to potential legal action.
  • Security. Drug testing can help avoid fraud, embezzlement, or other forms of workplace theft by employees trying to finance illicit addictions.
  • Reputation. Problems with any of the preceding issues can hurt a company’s good name, as can employees who are impaired or intoxicated while representing the company.
Workplace studies have demonstrated that sound drug-free workplace policies can reduce on-the-job accidents and absenteeism and improve productivity and worker retention.¹

Importance of a Clear Policy

When implementing a drug-free workplace policy, it’s critical, both legally and from an employee-relations standpoint, to set clear expectations. A well-designed workplace drug policy will explain how and when testing will be conducted, and what the consequences will be for failing a test or refusing to take one. State laws and regulations may also require displaying drug-free workplace policies at worksites.

Drug Testing Process

Drug testing begins with the collection of a specimen—typically urine, though saliva and hair also may be tested. Collection usually takes place at the test location. Direct observation of a subject during urine collection is generally forbidden, but technicians may accompany a subject into a restroom, listen as the specimen is collected, check its appearance and temperature, and use other methods as precautions against specimen tampering or substitution (e.g., requiring a test subject to wear a hospital gown to prevent concealment of “clean” specimens or adulterants, dying toilet water to prevent its use in diluting a specimen, etc.).

Once a specimen is collected, it is typically divided in half. One portion is tested, and the other is set aside for use in case of error or contamination, to confirm a positive test result, or to address any challenge to test findings.

What is Detected

Modern technology enables detection of a vast range of substances. Employers in industries where abuse of specific substances is a concern (makers and sellers of pharmaceuticals or supplements, e.g.) can order custom tests for virtually any substance—if, of course, they’re willing to pay for them.


5-Panel Tests

The most common drug-testing procedure is the 5-panel test used to screen employees in industries regulated by the U.S. Department of Transportation (DOT), including interstate truck drivers, commercial rail and flight crews, and Coast Guard personnel. Often administered in conjunction with alcohol breathalyzer checks, the 5-panel tests detect the following substances:

  • Amphetamines. Stimulants, or “speed,” taken in tablet form, snorted in powder form or smoked are extremely addictive and can cause sleep disorders, depression and suicidal behavior, violent mood swings, and heart attacks.
  • Cocaine. Extremely addictive, cocaine when snorted or smoked in crystalline “crack” form, it induces euphoria and manic behavior.
  • Opiates. Eaten, smoked, snorted or injected, natural opium, codeine, and heroin are highly addictive narcotics. They render users sleepy or even catatonic, and addicts experience severe pain and nausea when deprived of the drug; overdoses can be lethal.
  • Phencycladine (PCP). Highly unpredictable “angel dust” can induce hallucinations, paranoia, and violent outbursts.
  • Marijuana (THC). Smoked, “vaped,” or eaten, pot slows reflexes and reaction times, and can reduce attention span and alertness. While not physically addictive, it can be habit-forming. Effective at reducing nausea in chemotherapy patients and reducing some forms of chronic pain and anxiety, marijuana has been cleared for medical use in 29 states, and its recreational use is permitted in 9 states. While remaining classified as an illegal controlled substance under U.S. federal law, in states where marijuana has been legalized, employers may opt for a 4-panel drug test that eliminates the marijuana screen.

10-Panel Tests

More comprehensive 10-panel tests are gaining popularity with employers. In addition to the substances included in the 5-panel test, the 10-panel test detects five commonly abused prescription drugs:

  • Barbiturates. Known as “downers” or sedative-hypnotics, these drugs are used to aid sleep and reduce anxiety. Overdoses are lethal. Barbiturates are extremely dangerous because users’ bodies adjust to them over time, so that continually higher dosages (eventually approaching lethal levels) are needed to feel their effects.
  • Benzodiazepines. A family of tranquilizers that includes Xanax and Valium, these drugs are among the most commonly prescribed depressant medications in the United States. They are also habit-forming and widely abused.
  • Methadone. A synthetic, narcotic painkiller, it is used medically for pain relief and also as a replacement for morphine and heroin in addicts trying to wean off those drugs. The drug shares many effects and characteristics of morphine, and is also subject to abuse.
  • Methaqualone. Also known as Quaaludes, this barbiturate-like drug depresses the central nervous system. Abusers may appear drunk, with slurred speech and unsteadiness or even incapacitation. The drug is highly addictive and overdoses can be lethal.
  • Propoxyphene. Also known by the trade name Darvon, is no longer sold legally in the US, but it persists as a drug of abuse. Used to treat mild to moderate pain, it can cause heart damage, even at therapeutic doses.

Additional panel tests can be ordered at many labs to test for specific substances, including opioids such as Oxycontin and Oxycodone, which behave similarly to opiates in the body (and share their addictive nature), but are not detected by standard opiate tests.

False Positives

Panel tests employ paper strips impregnated with antibodies that react and change color in the presence of a drug or its metabolites—substances produced when a drug breaks down in the body. The panel tests, also known as immunoassays, detect drugs much the same way home pregnancy tests change color in the presence of pregnancy-related hormones.

Panel tests are quick, effective, and easy to conduct, but they are subject to “false positives,” which appear to detect a substance that isn’t actually found in the specimen. False positives occur when a substance in the specimen is chemically similar to the target substance. These “imposter” substances can be byproducts of prescription or over-the-counter medicines, nutritional supplements, and even certain foods.

Makers of immunoassay test materials continually refine the sensitivity of test panels to reduce the likelihood of false positives. Nevertheless, the vast (and growing) number of substances, particularly prescription drugs, that can masquerade as illicit drugs or their byproducts means false positives will always be an issue with immunoassay testing.

The table below is just a sampling:

Drug-Testing Target

Potential Source of False-Positive


Cold remedies, hay fever remedies, nasal decongestants, diet pills, fluoxetine (Prozac), methylphenidate (Ritalin), bupropion (Wellbutrin), beta blockers (blood-pressure remedies)


Sleep aids, ibuprofen (Motrin/Advil), naproxen sodium (Aleve)


Ibuprofen (Motrin/Advil), sertraline (Zoloft)


Coca tea


Ibuprofen (Motrin/Advil), hemp food products


Quetiopine (Seroquel)


Poppy seeds (no longer an issue with latest generation of panel tests)

Phencycladine (PCP)

Antihistamines, dextromethorphan (cough suppressant), ibuprofen (Motrin/Advil), diphenhydramine (Benadryl)

Proof-positive: Testing and Re-testing

To safeguard against false positives, drug testing labs re-test specimens that return positive panel-tests to rule out the possibility of a false positive. The confirmation tests use testing methods far more sensitive than panel tests—typically gas chromatography–mass spectrometry (GC-MS) or high performance liquid chromatography (HPLC).

These test methods are extremely precise and can distinguish between target substances and chemical imposters that can fool panel tests.

The Role of the Medical Research Officer (MRO)

A medical research officer (MRO) is a physician with expertise in substance abuse and drug testing. At a drug test lab, the MRO is responsible for reviewing all test results, ensuring that specimens are handled securely from the time of collection through the testing process, flagging any indication of specimen tampering or adulteration, and documenting all testing procedures.

In the case of a positive test result, the MRO may contact the test subject to check on any prescription medications, nutritional supplements, or over-the-counter medications they may be taking. In light of this information and the results of a GC-MS or HPLC confirmation test, the MRO can declare an accurate positive test result “false” if it detects a medically legitimate drug.

Finally, the MRO makes a final certification as to whether the individual being tested passes or fails. Results are typically returned to the employer within 1 to 2 business days. Employers conducting in-house testing will need to hire or contract with a trained MRO to ensure all testing procedures are ironclad and can withstand any legal challenges.

In Case of a Dispute

In cases where an employee or job candidate disputes a positive test result, their recourse varies from state to state. Unionized worksites may file grievances on behalf of an employee. In some jurisdictions, employers may give them the option of repeating the test using the portion of the original specimen that was set aside after collection. In some jurisdictions, the individual may have to pay for the second test procedure themselves.

Note that companies with 15 or more employees are subject to the Americans with Disabilities Act (ADA), which includes some addictions among the conditions for which employers must provide reasonable accommodations. Before drug-testing employees who are subject to the ADA, employers should be prepared to offer any required accommodations, which may include granting leave time for employees pursuing counseling or rehab.

As long as these requirements are met, the combined safeguards of a certified testing lab, verification of positive panel-test results with GC-MS or HPLC testing, and oversight by a qualified MRO make workplace drug testing highly reliable—and defensible in the event of any legal challenges.

False-positives are par for the course with workplace drug testing, but a well-designed and implemented testing policy can minimize their impact on drug-free workplaces.

pre-employment drug testing guide


1. "Employee Drug Testing: Study Shows Improved Productivity and Attendance and Decreased Workers’ Compensation and Turnover,” Neil A. Fortner, David M. Martin, S. Evren Esen and Laura Shelton; Journal of Global Drug Policy and Practice, 2011

Disclaimer: The resources provided here are for educational purposes only and do not constitute legal advice. We advise you to consult your own counsel if you have legal questions related to your specific practices and compliance with applicable laws.

Jim Akin

Jim Akin


Jim Akin is a Connecticut-based freelance writer and editor with experience in employee relations, media relations, and social-media outreach. He has produced content and managed internal communications, business-to-business outreach, and consumer-focused campaigns for clients including Experian, VantageScore Solutions, Pitney Bowes, Medtronic, Microsoft, and Coca-Cola.

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