Addiction Medicine podcast

#18 Urine Drug Testing with Dr. Timothy Wiegand

August 17, 2023 | By



Interpret urine drug tests (UDT) like a toxicologist! Learn how to approach interpreting positive opiates, opioids, and benzodiazepines in UDT. We discuss the nuances of interpreting UDT, false positives,  and how to counsel a patient prior to ordering the test. We’re joined by Dr. Timothy Weigand @TwToxMD (University of Rochester Medical Center).

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Show Segments

  • Intro, disclaimer, guest bio 00:00
  • Guest one-liner: 05:17
  • Case from Kashlak: 09:42
  • Types of Urine Drug Testing (UDT): 10:37
  • Detection Window 22:07
  • Interpreting Opiates and Opioids UDT 25:26
  • Resources to Interpret UDT 39:20
  • False Positives  43:29
  • Discussing Results with a Patient 45:52
  • Interpreting UDT – Buprenorphine 48:47
  • Specimen Validity Testing  50:22
  • Saliva Testing 54:56
  • Outro 1:01:28

Urine Drug Testing Pearls

  1. Before ordering a urine drug test (UDT), be sure to let the patient know what the purpose of the test is and how it will be used to help guide their clinical care. 
  2. Screening UDTs are often the initial test to screen for common substances, as they are cheap and easy to use. Of note, they are prone to false positives.
  3. Confirmatory UDTs utilize gas or liquid chromatography and are often paired with mass spectrometry. This method is expensive and takes more time to obtain results, yet can be helpful to determine if a “positive” test on a UDT screen is a true positive.
  4. The window of detection for a substance is typically 1-3 days in a UDT, though this window can vary based on the frequency, amount of use, and specific substance.
  5. On screening UDT a positive opiate test could mean exposure to codeine, morphine heroin, or be a false positive.
  6. On confirmatory UDTs for opioids & opiates, be sure to know how these substances are metabolized, as this can help you determine what the original substance an individual was exposed to. See Opioid/Opiate Metabolism Chart
  7. Amphetamine presence on a screening UDT is prone to false positives, caused by many common medications (e.g. bupropion, pseudoephedrine), be sure to send a confirmatory test if a positive test will impact care.
  8. Be supportive, not accusatory when discussing with a patient unanticipated UDT findings.
  9. Specimen validity testing involves making sure a UDT is valid, and this can be done through many mechanisms (e.g. temperature strip, urine creatinine, urine pH, and specific gravity).

Urine Drug Testing Notes

Type of Urine Drug Testing (UDT) 

Before ordering a UDT be sure to engage with the patient, and discuss the purpose of the test, as well as how the results will be used. Consider using it as a harm reduction tool as well, so individuals can be aware if there are any adulterated substances they are being unintentionally exposed to (e.g. individual thinking they are only using cocaine, also tests positive for fentanyl suggesting an adulterated drug supply)

Screening Testing: 

The initial test to screen for substances is often a screening immunoassay which utilizes antibody technology. A common panel may test for substances such as THC, opiates, opioids, amphetamines, barbiturates, and cocaine. These are tests where the results can be obtained quickly such as a point of care test (POCT) or being sent down to a lab to run. Since these tests are antibody-based, it is possible for other substances to be similar in structure and cross-react with the test to cause a false positive.  Pros of these tests are that they are: cheap and easy to use. Cons include that they can be prone to false positives and misinterpretation and may have substances left off on the initial screening panel (Moehler, 2017).

Remember opioids are NOT included in the opiate UDT screen (e.g. fentanyl, methadone, and buprenorphine are NOT opiates) 

Dr. Wiegand recommends that it’s also important to remember to know what you can’t test for on a screening UDT.  Dr. Stahl reminds us that many locations may not automatically include a test for fentanyl, and this test may need to be ordered separately depending on your institution. 

Confirmatory Testing: 

Confirmatory testing uses gas or liquid chromatography and is often paired with mass spectroscopy  (Moehler, 2017). It is more expensive than screening tests and it takes more time to get the results. You are not going to have false positives on this test, so confirmatory testing can be helpful to determine if a “positive” test on the screen is a true positive.  Dr. Wiegand sends confirmatory tests when it is going to impact patient care. He recommends considering the use if there are legal issues, child protective services issues, or other specific high stake scenarios.  

Window of Detection 

In general, if there is a single use of most substances, it can typically be detected for 1-3 days in the UDT. This window of detection may vary based on a number of the following factors  (Moehler, 2017).

  • Frequency of use 
  • How much is used
  • Specific substance (e.g. half-life, drug metabolites)
  • Individual patient characteristics
  • Medium of testing (example: hair, saliva, urine, can have different windows of detection)

Notably, individuals with heavy, regular, fentanyl use can still be positive in their UDT for a long period of time such as weeks from their last use due to its lipophilicity (Huhn, 2020).

Cannabis can also be positive for extended periods of time from individuals who had heavy, regular use.  THC/Creatinine ratios can be helpful in showing a downward trend of use over time (Smith, 2009).

Interpreting Opioid, Opiate UDT 

It’s important to remember that on a UDT panel, opiates are different than opioids. Opiates are substances naturally derived from the opium plant (e.g. codeine, morphine). Opioids are synthetic and semi-synthetic. There can be variability in the opioids that your institution panel tests for (e.g. oxycodone, fentanyl, hydromorphone).  After a positive opiate and opioid screening test occurs, confirmatory testing can be helpful in determining the opioid or opiate an individual was taking. Utilize an opioid and opiate metabolism chart to help guide your interpretation of these results, as based on the metabolites present there could be a few possible interpretations due to the overlap in the breakdown of the parent compound to the metabolites. See Opioid/Opiate Metabolism Chart

Below are some pearls from Dr. Wiegand on interpreting positive opioids and opiates on screening UDT.

Positive Opiates: Exposure to codeine, morphine, heroin, or false positive (hydrocodone or hydromorphone may cross-react with a screening test)

Positive  (synthetic) opioids: Institutional dependent, often include oxycodone and methadone

Interpreting Benzodiazepine UDT

Most benzo screens are specifically targeted to detect the metabolite oxazepam. This is a common metabolite for a number of benzos such as diazepam and chlordiazepoxide. Some benzos will not cross-react. For example, clonazepam is not likely to cross-react with oxazepam and is often not detected on screening UDT.  Dr. Wiegand reminds us that some benzos still will cross-react with the oxazepam screening assay. This cross-reactivity can be dose-dependent. 

In addition, there are many designer benzos at this time in our community supply that may not be detected on the screening test. A common cause of false positives on benzo screening UDT test may be from the medication sertraline (Nasky, 2009).  Utilize a confirmatory test, and refer to a benzo metabolism chart to help guide interpretation if clinically indicated. Benzo Metabolism Chart

Interpreting Buprenorphine UDT

Buprenorphine is metabolized to norbuprenorphine, buprenorphine-3-glucuronide (bup-g) and norbuprenorphine-3-glucuronide (norbup-g) (Furo, 2021). If an individual is taking buprenorphine in general, you see a higher level of norbuprenorphine compared to the buprenorphine parent compound (Donroe, 2017).  If there is only buprenorphine present and none of the metabolites, it suggests an individual may have interfered with their UDT specimen. 

Common False Positives:

Below are a few examples of potential medications that can cause a false positive on a screening UDT for the specific substance listed.

Common medications that can cause false positive fentanyl on a screening UDT: risperidone, trazodone* (*risk of false positive may be kit dependent), labetalol, and ziprasidone  (Waters, 2022; Wang, 2014; Wanar, 2022; Gourlay, 2010). 

Common medications that can cause false positive oxycodone on a screening UDT: naloxone and naltrexone (Jenkins, 2009; Plant, 2019)

Common medications that can cause false positive amphetamine on a screening UDT: bupropion, pseudoephedrine (decongestant), OTC Vick’s decongestant (has L-amphetamine, technically a true positive)   (Moehler, 2017).

A common medication that can cause false positive benzodiazepine on a screening UDT: sertraline  (Moehler, 2017).

Common medications that can cause false positive phencyclidine (PCP) on a screening UDT: dextromethorphan, carbamazepine, tricyclic antidepressants (TCAs), and venlafaxine (Moehler, 2017; Masternak, 2021)

Discussing with a Patient Unanticipated UDT findings

Be supportive, not accusatory, and ask questions to better understand the meaning of the unanticipated result to the patient. Don’t jump to conclusions with your test results. Use results to help support a patient in their recovery, as well as remember that this is only part of the information and involve the patient in a dialogue. Be sure to avoid stigmatizing terms such as a “dirty” or “clean” drug test.  Take the setting into consideration as well to discuss the results, e.g. if family members are present, consider bringing back the discussion when the patient is alone. 

Specimen Validity Testing

Specimen validity testing ensures the validity of a UDT by verifying the adequacy of the sample. A UDT may become invalid if an insufficient amount of sample is collected. Similarly, an oral saliva test can be deemed invalid if there is an inadequate amount of saliva for the oral test. The lab report includes various markers that can provide insight into the validity of the testing such as the following (ASAM: Appropriate Use of Drug Testing in Clinical Addiction Medicine Consensus Document).

  • Temperature strip on the side of a UDT – should be around body temperature
  • Urine Creatinine (too dilute or too concentrated): if outside of the normal range the sample is not valid. There could be physiologic reasons why it is too dilute, or it could be because someone added water to the sample, or drank a lot of fluid prior to the test.
  • Urine pH: should be within a normal range
  • Specific gravity of urine

If a specimen is invalid, then so is the interpretation. Try to minimize the intrusion of obtaining a sample, as many patients have a history of trauma. Dr. Wiegand recommends considering observing someone complete saliva testing may be one option to provide to patients over a UDT if, for some reason, a test must be observed.

Oral Saliva Testing

It can take time to get enough saliva from some patients due to dry mouth, and it is important to review the window of detection with different substances using this testing method as it can vary from a UDT. For example, the THC window of detection is lower than in UDT (Niedbalda, 2001). There are still ways to invalidate this test.

In addition, buprenorphine results will only tell you if it is present or not (not quantity). If a patient has recently taken a buprenorphine film, an oral saliva test will be positive even if it is not taken routinely. False negative buprenorphine can occur if there is not an adequate saliva sample. Many patients are on medications that cause dry mouth, so a false negative for buprenorphine may be more likely with the oral saliva testing.

Additional Resources

Dr. Wiegand recommends using resources such as ASAM: Appropriate Use of Drug Testing in Clinical Addiction Medicine Consensus Document, PubMed search, or pulling a test package insert to look for data on cross-reactivity in screening tests, referring to different opioid and benzo metabolism charts to interpret analytes. 

Take Home Points

  • Learn what analytes are tested for on your home institution’s UDT panel.
  • Be aware of common false positives when interpreting UDT.
  • Understand specimen validity testing and how to apply that in your own practice.
  • Know where to go for additional resources to correctly interpret UDT. 


  1. ASAM Pocket Guide on Appropriate Use of Drug Testing in Clinical Addiction Medicine 
  2. ASAM: Appropriate Use of Drug Testing in Clinical Addiction Medicine Consensus Document
  3. Addiction Toxicology Case Conference: First Friday of the month: Supported by ACMT/ASAM 


Listeners will develop an approach to interpreting urine drug testing results.

Learning objectives

After listening to this episode listeners will…  

  1. Compare and contrast the advantages and disadvantages of screening (immunoassays), confirmatory tests (gas chromatography/mass spectrometry), and POCT urine drug testing. 
  2. Describe the common length of detection time of substances in the urine.
  3. Describe how to interpret opioid, opiate, and benzodiazepine UDS test results. 
  4. Describe results that may suggest tampering with urine drug screens and develop an approach to have a conversation with the patient. 


Dr. Wiegand reports no relevant financial disclosures. The Curbsiders report no relevant financial disclosures. 


Chan, CA. Wiegand T, Stahl N, Sonoda K. “#18 Urine Drug Testing with Dr. Timothy Wiegand”. The Curbsiders Addiction Medicine Podcast. August 24, 2023.

Episode Credits

Producer: Natalie Stahl, MD, MPH
Show Notes, Cover Art, Infographic: Carolyn Chan, MD, MHS
Hosts: Carolyn Chan, MD, MHS, and Natalie Stahl MD, MPH
Reviewer: Kento Sonoda, MD
Showrunner: Carolyn Chan, MD, MHS
Technical Production: PodPaste
Guest: Dr. Timothy Wiegand

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The Curbsiders are partnering with VCU Health Continuing Education to offer FREE continuing education credits for physicians and other healthcare professionals. Visit and search for this episode to claim credit.

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