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Fentanyl False Positives

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False positives for the presence of fentanyl can occur on drug tests for several reasons, including cross-reactivity with other substances, sample contamination, or defective testing equipment. Several substances can produce false positives, showing up on personal fentanyl test strips and lab screens using urine samples. In many cases, it’s vital to determine if fentanyl is in a substance because the drug’s potency is up to 100 times higher than morphine—even a tiny amount can kill the average person.

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How Is Fentanyl Presence Checked?

The presence of fentanyl can be detected using lab tests or test strips. Lab tests are typically administered in clinical settings. Test strips may or may not be available based on the state in which you are located. In many states, they remain illegal as they are considered drug paraphernalia. However, in January 2023, lawmakers in Florida “filed legislation that would add Florida to a growing list of states that have moved to decriminalize or legalize fentanyl test strips.” (1)

Urine samples are the most common method of detecting fentanyl and other drugs. (2) However, in some cases, clinical tests use blood or hair samples, or saliva can be obtained using a mouth swab.

Fentanyl test strips are small paper strips designed to identify the presence of fentanyl in a substance, such as heroin. (3) They are used as a harm reduction method for people who misuse drugs, particularly those who use opioids, to determine if their drug supply is tainted with fentanyl.

How Do False Positives Occur When Testing?

Although many types of drug tests tend to be very accurate, false positives can occur for many reasons, including contamination or improper administration.

Reasons for False Positives Include:

  • Contamination—Urine samples can be contaminated by environmental factors or substances that can interfere with test results. For example, if the person taking the test was exposed to fentanyl in the environment or handled a fentanyl-contaminated substance, it may lead to a false positive result.
  • Improper Test Administration—Urine drug tests must be administered correctly to ensure accurate results. Failure to follow the proper collection, storage, and handling procedures can produce false positive results.
  • Cross-Reactivity—Urine drug tests use antibodies that bind to specific drugs or metabolites. (4) Sometimes, these antibodies cross-react with other substances, producing a false positive. For example, some medications, such as antidepressants or antipsychotics, can cross-react with fentanyl drug tests and render a positive result, even when fentanyl is absent.

Medications Reported to Cause False Positives for Fentanyl Include:

  • Codeine, an opiate and common pain reliever.
  • Tramadol, an opioid pain reliever.
  • Diphenhydramine, an antihistamine often used to treat allergies.
  • Methadone, a medication used to treat opioid addiction.
  • Poppy seeds, which can contain trace amounts of opiate alkaloids from which fentanyl is derived.

Can Standard Urine Drug Screens Detect Fentanyl?

Most standard urine drug screens do not specifically test for fentanyl. However, some urine drug screens may detect the presence of opiates or opioids in general (including fentanyl), depending on the specific panel used.

Traditional urine drug screens typically test for common drugs such as marijuana, cocaine, amphetamines, opioids (such as morphine and codeine), and benzodiazepines. Fentanyl is a synthetic opioid and may not be detected by the standard opioid panel.

What Metabolites Do Drug Screens Look For?

Fentanyl drug screens typically look for fentanyl’s metabolites, the drug’s breakdown products produced by the body after ingestion. The most common of these detected in drug screens include norfentanyl, despropionyl fentanyl, and hydroxy fentanyl. Metabolites are easier to detect and have longer half-lives than the parent drug. This allows for an extended detection window to help identify recent drug use.

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What Specific Tests Are Used To Prevent Fentanyl False Positives?

To prevent fentanyl false positives, specific tests designed to detect fentanyl or its metabolites may be used. These tests include:

  • Fentanyl Urine Test Strips—These strips are more accurate than urine samples provided in a cup and are designed to detect the presence of fentanyl in urine samples specifically. They use antibodies that attach to fentanyl and produce a color change, indicating fentanyl’s presence.
  • Immunoassays—These are highly sensitive lab tests that use antibodies to detect fentanyl in urine samples. (5)

Gas Chromatography-Mass Spectrometry (GC-MS)—This is a very specific test that can detect fentanyl’s presence or metabolites in urine samples. It can also differentiate fentanyl from other substances that could yield false positive results. (6)

Risks of False Positives & False Negatives for Fentanyl

The risks of negative and false positive results when testing a substance for fentanyl can have significant consequences.

False Negative Results

If a person tests a substance for fentanyl and receives a negative test result, they may continue to use drugs without knowing the risks they’re facing. In this way, false negative results can lead to a false sense of security.

False Positive Results

False positive results can result in loss of employment for individuals who did not use fentanyl. False positive results can also have significant legal implications, such as when drug testing is used for probation or child custody. False positives can also damage an individual’s reputation and the integrity of the entity that administered the test.

What To Do in Case of Overdose

A fentanyl overdose is a medical emergency that requires immediate attention. If you suspect a person is overdosing on fentanyl or other opioids, you are urged to do the following:

  • Call 911 or local emergency services immediately.
  • Administer naloxone, if available. If you do not have naloxone, emergency responders may do so when they arrive.
  • Remain close to the person until help arrives.
  • Monitor the person’s breathing and keep them conscious if possible. If unresponsive, turn them on their side to prevent choking.
  • If they stop breathing, perform CPR.
  • Provide any information you have as requested by emergency responders.

Follow up with medical care and addiction treatment if needed.

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If you have been misusing fentanyl or drugs that may contain fentanyl, entering into a drug treatment program that utilizes a comprehensive approach to addiction treatment can be extremely beneficial.

When you contact Guardian Recovery you will be put into contact with a Treatment Advisor today who will explain our evidence-based programs and multiple levels of care. You can also receive a free, no-obligation assessment and health insurance benefits check. Addiction is a chronic medical condition, and although not curable, it is very treatable, and we can help. Reach out to us today to learn more.


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Disclaimer: Does not guarantee specific treatment outcomes, as individual results may vary. Our services are not a substitute for professional medical advice or diagnosis; please consult a qualified healthcare provider for such matters.

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Reviewed professionally for accuracy by:

Ryan Soave


Ryan Soave brings deep experience as a Licensed Mental Health Counselor, certified trauma therapist, program developer, and research consultant for Huberman Lab at Stanford University Department of Neurobiology. Post-graduation from Wake Forest University, Ryan quickly discovered his acumen for the business world. After almost a decade of successful entrepreneurship and world traveling, he encountered a wave of personal and spiritual challenges; he felt a calling for something more. Ryan returned to school and completed his Master’s Degree in Mental Health Counseling. When he started working with those suffering from addiction and PTSD, he found his passion. He has never looked back.

Written by:

Cayla Clark

Cayla Clark

Cayla Clark grew up in Santa Barbara, CA and graduated from UCLA with a degree in playwriting. Since then she has been writing on addiction recovery and psychology full-time, and has found a home as part of the Guardian Recovery team.

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