How to explain failed drug test? Understand false positives and the MRO process

October 6, 2025 •

5 min read

According to research from Boston Medical Center, false positive results can affect 5% to 10% of initial drug screens. Learning how to explain failed drug test results, particularly due to legitimate medication use, is crucial for protecting your employment and reputation.

Quick Summary

This guide provides a comprehensive overview of explaining inaccurate drug test results caused by prescribed or over-the-counter medications. It details the pharmacology behind false positives, explains the vital role of the Medical Review Officer (MRO), and outlines actionable steps for disputing erroneous outcomes.

Key Points

False Positives Are Common: Initial immunoassay drug tests can produce false positives due to cross-reactivity with legal substances, including many prescription and OTC medications, affecting up to 10% of results.
The Medical Review Officer is Key: The Medical Review Officer (MRO) is a licensed physician who confidentially verifies if a positive test has a legitimate medical explanation, like a valid prescription.
Document Everything: To explain a failed drug test, gather complete records of all medications, supplements, and foods that could interfere, such as prescription details and a letter from your doctor.
Request Confirmatory Testing: A GC-MS confirmatory test is far more accurate than the initial screening and can resolve false positives by providing definitive identification of the substance.
Know Your Rights: The Americans with Disabilities Act (ADA) provides protections for employees using legitimate prescription medication for a medical condition.
Communicate Professionally: When speaking with your employer, provide the verified medical explanation from the MRO in a calm and professional manner to avoid misunderstanding.
Stay Proactive: Do not ignore a positive result. Immediately engage with the MRO process and gather necessary documentation to swiftly resolve the issue.

Understanding the Pharmacology Behind False Positives

Many initial drug screenings, particularly common urine immunoassays, are designed for speed and cost-effectiveness. These tests use antibodies to detect the presence of certain drug molecules or their metabolites in a sample. The primary limitation of this method is that some legal substances, including prescribed and over-the-counter (OTC) medications, share a similar molecular structure with illicit drugs. This phenomenon, known as cross-reactivity, can trigger a false positive result.

The Science of Cross-Reactivity

Initial immunoassay tests are presumptive, not definitive. They operate on a 'yes/no' principle, indicating the possible presence of a substance. For example, the chemical structure of some amphetamines is similar to certain decongestants or antidepressants, causing the immunoassay to mistake one for the other. A confirmed positive result, which occurs after a more specific and accurate test like gas chromatography/mass spectrometry (GC-MS), is far more reliable.

Common Medications That Cause False Positives

Several legitimate medications are known to cause false positive results on initial drug screenings. The following are some of the most common examples:

Amphetamines/Methamphetamines: The antidepressant bupropion (Wellbutrin), ADHD medications like methylphenidate (Ritalin) and atomoxetine, and OTC decongestants containing pseudoephedrine (Sudafed) or phenylephrine are frequent culprits.
Opioids/Opiates: Poppy seeds (due to trace morphine/codeine content), quinolone antibiotics (e.g., ofloxacin, levofloxacin), and the antidepressant trazodone can cause false positives for opiates. The cough suppressant dextromethorphan (Robitussin) can also be a factor.
Cannabinoids (THC): Nonsteroidal anti-inflammatory drugs (NSAIDs) like ibuprofen (Advil) and naproxen (Aleve), and proton pump inhibitors such as pantoprazole (Protonix) have been linked to false positives for THC. CBD products, especially unregulated ones, can also contain enough THC to cause a positive result.
PCP (Phencyclidine): Diphenhydramine (Benadryl), ibuprofen, and tramadol can cross-react with initial screens for PCP.
Benzodiazepines: The antidepressant sertraline (Zoloft) can sometimes trigger a false positive result for benzodiazepines.

The Medical Review Officer (MRO) Process

When a drug test yields a preliminary positive result, it is not immediately reported to the employer as a confirmed positive. Instead, the process is handled by a Medical Review Officer (MRO), a licensed physician specially trained to interpret drug test results.

The MRO's Role in Result Verification

The MRO's primary function is to determine if there is a legitimate medical explanation for a confirmed positive result. This confidential review process protects the individual's privacy and ensures the accuracy of the test results before any employment action is taken. The MRO acts as a bridge between the testing laboratory and the employer, preventing misinterpretation of findings. For Department of Transportation (DOT) testing, MRO involvement is a mandatory step.

The Confidential MRO Interview

If your test comes back as a presumptive positive, the MRO will attempt to contact you confidentially. During this interview, you will have the opportunity to provide a legitimate medical explanation for the result. This is the time to disclose any prescription or OTC medications you are taking that may have interfered with the test. The MRO will verify any prescriptions with your doctor or pharmacy to confirm their validity. If your explanation is confirmed and deemed legitimate, the MRO will report the final result to your employer as negative.

A Step-by-Step Guide on How to Explain Failed Drug Test Results

If you find yourself facing an unexpected positive drug test, taking a professional and proactive approach is essential. Here are the steps to follow to clear your name and resolve the situation.

1. Stay Calm and Professional

It is natural to feel stressed or anxious, but it's important to maintain your composure. A calm demeanor during conversations with your employer or the MRO can help ensure a productive outcome. Avoid becoming defensive and focus on presenting a clear, factual account of events.

2. Gather Your Documentation

Before speaking with the MRO, gather all relevant medical documentation. This includes:

A list of all prescription medications you are currently taking, including dosages and prescribing physician information.
Copies of prescription labels or medical records.
A list of any OTC medications, vitamins, or supplements you have taken recently.
A list of any potentially interfering foods you've consumed, such as poppy seeds.

3. Communicate Clearly with the MRO

When the MRO contacts you, be transparent and provide all relevant information and documentation. This is a confidential medical discussion, and the MRO is trained to handle these situations with discretion. Their job is to verify your medical claims and protect your privacy.

4. Request a Confirmatory Test

If you believe the initial screening was a false positive, you have the right to request a retest or a more accurate confirmatory test, such as GC-MS. A confirmatory test is far more sensitive and specific, and can accurately distinguish between chemically similar substances, resolving any ambiguity from the initial screen.

5. Communicate with Your Employer

After the MRO has verified your legitimate medication use and cleared the result, the MRO will report a negative finding to your employer. If the situation is not resolved to your satisfaction, or you are in a non-DOT regulated position without MRO review, approach your employer professionally. Present your medical evidence and explain the situation clearly, emphasizing that the result was due to a legitimate, prescribed medication. Remember, federal law under the Americans with Disabilities Act (ADA) may offer protections regarding certain medical conditions and their treatment.

Comparison of Drug Test Screening and Confirmatory Testing


Feature	Immunoassay (Screening)	Gas Chromatography/Mass Spectrometry (Confirmatory)
Accuracy	Presumptive; higher rate of false positives due to cross-reactivity.	Highly specific and reliable; considered the gold standard for accuracy.
Speed	Rapid, often providing results within minutes or hours.	Slower, as it requires more complex lab procedures.
Cost	Less expensive.	More expensive due to specialized equipment and expertise.
Principle	Uses antibodies to detect a general class of drugs based on molecular similarity.	Separates individual molecules and identifies them based on their unique chemical 'fingerprint'.
Result Type	Presumptive Positive or Negative.	Verified Positive or Negative.

Protecting Your Rights and Privacy

When legitimate prescription medication use results in a failed drug test, employees have legal rights to consider. The Americans with Disabilities Act (ADA) prohibits discrimination based on a disability, and the use of prescription medication for a medical condition is generally protected. Employers are required to maintain confidentiality regarding an employee's medical information. If your employer is concerned about safety-sensitive job functions, they must engage in an 'interactive process' to determine if a reasonable accommodation is possible, not just assume impairment. This process involves discussing the issue with the employee to understand any restrictions and potential impacts. For DOT-regulated positions, the MRO plays an official role in this process.

For more detailed information on regulations and your rights, resources like the Department of Transportation Office of Drug and Alcohol Policy and Compliance can provide authoritative guidance, especially for safety-sensitive roles.

Conclusion

Receiving a positive drug test result due to a false positive can be a jarring and stressful experience, but it is not an insurmountable challenge. The key to successfully navigating this situation is a calm, factual, and proactive approach. By understanding the pharmacology of cross-reactivity, documenting your legitimate medication use, and working confidentially with a Medical Review Officer, you can resolve the issue with minimal disruption. Taking the right steps and knowing your rights protects your reputation and ensures that your medical history remains a confidential matter between you and your healthcare provider.

Frequently Asked Questions

A false positive drug test occurs when a non-illicit substance, like a legal medication or certain food, triggers a positive result on an initial drug screening because its molecular structure is similar to that of an illegal drug.

You can prove a positive result was caused by medication by providing the Medical Review Officer (MRO) with a valid prescription from your doctor for the medication in question. The MRO will confidentially verify the prescription with the prescribing physician or pharmacy.

A Medical Review Officer (MRO) is a licensed physician who is responsible for reviewing and interpreting drug test results to determine if a legitimate medical explanation, such as a valid prescription, exists for a positive result before reporting it to an employer.

Yes, some over-the-counter (OTC) medications can cause a failed drug test due to cross-reactivity. Examples include certain nasal decongestants like pseudoephedrine, pain relievers like ibuprofen, and antihistamines like diphenhydramine.

A confirmatory test, such as gas chromatography/mass spectrometry (GC-MS), is a highly accurate test used to verify the results of an initial screening. It is crucial because it can definitively identify the specific substance in your system, distinguishing a true positive from a false positive.

You are not required to disclose your specific medications to your employer. The Medical Review Officer (MRO) process is confidential. You only need to provide medical information to the MRO, who will report the final, verified result (negative if legitimate) to your employer.

If your employer does not use a Medical Review Officer (MRO), you should still gather documentation and calmly present the evidence of legitimate medication use to a human resources representative. You can also request an independent confirmatory test. Legal protections under the Americans with Disabilities Act (ADA) may still apply, especially if your job is not safety-sensitive.

Yes, consuming poppy seeds can lead to a positive result for opiates on an initial immunoassay screening. Poppy seeds contain trace amounts of morphine and codeine, but a confirmatory GC-MS test would be able to distinguish this from abuse.

If you are offered a retest after a false positive, it is important to communicate with your healthcare provider to ensure that your medication regimen or any other factors are accounted for. Being proactive and transparent about your situation with the MRO is the best approach.