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Clinical Drug Monitoring & Medication Adherence
Brought to you by Quest Diagnostics and Practical Pain Management

Scenario: Finding THC in Test Results for a Patient on Opioids and NSAIDs

Conditions addressed
chronic cervical radiculopathy, back pain, and knee pain

Medications addressed
hydrocodone/acetaminophen, ibuprofen, lidocaine

Image: iStock

Patient Case
A 52-year-old male with chronic cervical radiculopathy, back pain, and knee pain presents to his physical medicine and rehabilitation (PM&R) clinic for a regularly scheduled appointment. His pain has persisted since involvement in a serious car accident 3 years prior. As part of his agreement with the clinic, the patient undergoes annual urine drug monitoring. The patient’s pain medication regimen consists of:

  • hydrocodone/acetaminophen, 10 mg/325 mg every 6 hours as needed for back and knee pain
  • ibuprofen, 600 mg every 6 hours as needed for radiculopathy
  • a lidocaine 5% patch, once daily for back pain

After further discussion, the patient admits to taking cannabidiol (CBD) oil because it “really seems to help his knee pain” and he “knows he can’t get high on it.”


Patient Use of Marijuana or Cannabidiol

Many patients may want help with a medical or psychological problem they are experiencing but may not wish to take more medications; they may lean toward finding a “natural” remedy without fully understanding its safety profile or risk. CBD products and, depending on the state, marijuana may be easier to access for these patients than a visit to their prescriber and pharmacy.

Marijuana contains multiple cannabinoids, one of the most well-known being the psychoactive component, tetrahydrocannabinol (THC).1 Some individuals utilize marijuana specifically for its psychoactive properties while others use it because they find it helps with various afflictions. Some individuals claim both recreational and medical use of marijuana. Based on survey data from approximately 170,000 US adults that use marijuana, individuals with documented medical conditions were more likely to use marijuana than those without a medical condition.2

CBD is another cannabinoid that comes from the cannabis plant but it does not have psychoactive properties or produce psychoactive metabolites.CBD vendors may boast the substance’s ability to treat anxiety, sleep disorders, nausea, seizures, and pain, among other conditions. Only one CBD product, Epidiolex, has an FDA-approved indication for treatment of seizures associated with Lennox-Gastaut syndrome or Dravet syndrome.4

Drug Monitoring for Tetrahydrocannabinol (THC, marijuana)

Urine drug monitoring is one of the most frequently utilized methods to screen for use of THC and other substances.5 These tests commonly detect the 11-nor-delta-9-tetrahydrocannabinol-9-carboxylic acid metabolite of THC but may detect other metabolites as well.Detection of THC in the urine is contingent on the frequency and duration of use, hydration status when the urine is collected, the quality of the substance used, and the individual’s fat content (THC is fat soluble and stored in adipose tissue).5 Table I shows the duration of detectability in urine after use. THC may also be detectable in oral fluid (which typically tests for parent THC, not metabolite), blood, and hair with hair samples providing the longest window of detection.

Data based on Reference 5.

Note that passive inhalation of marijuana rarely causes THC accumulation of 50 ng/mL to trigger positive results on urine drug tests, especially in a setting where the individual is not within a confined space.5,6

Drug Monitoring for Cannabidiol (CBD)

CBD products, on the other hand, should never result in a positive THC screening because CBD is not metabolized into THC.3 Federal law states that, in order for CBD products to be utilized legally, they must have no more than 0.3% THC by dry weight.7 However, manufacturing of CBD products is not regulated, and consumers run the risk of using a product with more than 0.3% THC present.

Bonn-Miller, et al. utilized liquid chromatography (LC) to investigate the THC content of 83 CBD extract products sold online.8 The researchers discovered that 21% of these products contained THC with a varying concentration of 0 to 6.43 mg/mL. The latter amount is more than double the federal limit to be considered CBD. THC content beyond that of which is on the label of the product may occur for several reasons. For instance, activation of THC-producing genes may occur as a result of reproduction between a male and a female hemp plant.9 Farmers wishing to keep their products federally compliant typically only grow female hemp plants.9 Another possible culprit is a poor CBD extraction process that leaves behind unwanted THC.9

Importance and Frequency of Drug Monitoring

There are no guidelines that address frequency of drug monitoring specifically for THC or CBD products. The US Centers for Disease Control and Prevention (CDC) have, however, released guidelines for prescribing opioids for patients with chronic pain, as in the patient case presented above. These guidelines encompass drug testing and recommend obtaining a baseline urine drug test followed by, at a minimum, annual testing as a universal risk-management strategy and effort to maintain patient safety.10 Consensus recommendations from Argoff et al also suggest annual urine drug monitoring for patients prescribed opioids for chronic pain with a low risk of opioid misuse. Additionally, the authors suggest testing at least twice annually for patients at moderate risk, and at least 3 times annually for high risk patients. Further, urine drug monitoring should be performed as clinically necessary.11 (Watch a related video on why clinical drug monitoring is important.)

Some prescribers may conduct more frequent testing to confirm that patients are taking their medications as prescribed and that they are only taking those medications. The most recent Quest Diagnostics Health Trends report found that 51% of Quest drug monitoring test results showed evidence of potential misuse of prescription medications.12

Drug monitoring is also imperative for assessment of medication compliance, remission, and relapse in patients undergoing substance abuse treatment.13 According to the US Substance Abuse and Mental Health Services Administration (SAMHSA), those undergoing opioid abuse treatment must receive at least 8 drug tests per year.13 The true frequency of testing should be based upon a patient’s success in treatment. Some patients may require testing several times weekly to maintain sobriety whereas others may do well with monthly testing. Additionally, certain states may require more frequent testing than SAMHSA.13 Drug monitoring of patients receiving psychological treatment for a diagnosed mental illness is not common practice; it may become prudent should a patient present with mood or behavioral changes.5 Testing in this situation may help behavioral health practitioners exclude substance use as a potential contributing factor to their patients’ psychiatric symptoms. (See also, our case scenario on drug monitoring in patients undergoing medication-assisted treatment.)

What Tests are Available?

Both presumptive (also known as preliminary or qualitative) and definitive (also known as confirmatory) testing are available for THC but not for CBD. You can view Quest’s test code directory, for example, at: test-code-directory#. See the 2 main types of urine drug monitoring tests. Table II shows some commonly available laboratory cannabinoid tests.


P indicates presumptive; D indicates definitive; M indicates medMATCH service offered by Quest - reports indicate whether the prescribed drug(s), as specified by the ordering provider, or other drugs are detected in a specimen; LC indicates liquid chromatography; IA indicates immunoassay; MS indicates mass spectrometry; GC indicates gas chromatography. Data based on Reference 14 and communication with a Quest Diagnostics representative via phone on 01/21/2020.

Interpretation and Discussion of Drug Monitoring Results

In any setting, it is important for the provider to explain why a patient is being tested, how the provider will use the results, and that the results are confidential despite what they may show.5 Patients are likely to benefit from a thorough, yet simple, explanation of their results including why a test was positive or negative, and what the results may mean in terms of their treatment plan.5 (See a related video on how to discuss drug monitoring results with a patient.)

Expectations regarding findings of illicit substances or nonprescribed medications should be introduced during a patient’s first visit, before prescribing, and be presented in a nonjudgmental manner. For example, if a patient is being treated for a substance use disorder, a provider may explain that unexpected monitoring results could signal that a change in treatment is necessary. If urine drug monitoring frequently shows the presence of illicit or nonprescribed opioid substances, a referral for substance abuse treatment and/or a discontinuation of opioid therapy may be necessary. Providers are encouraged to use a Patient Agreement when prescribing opioids and controlled substances (see examples).

Returning to the patient case, the preliminary urine drug test yielded the results shown in Table III.


Fifty (50) ng/mL is the Quest Diagnostics’ laboratory cutoff for a preliminary positive result for THC.14 If an individual tests positive for THC, the clinician should initiate a conversation with the patient to see if they can explain the test result. During this conversation, it is important to ask the patient about any prescription and nonprescription substances, vitamins, and supplements they may be taking. The case patient presented here has already endorsed utilization of CBD oil, which means THC contamination may be possible. However, it is also important to note other potential reasons for the positive THC result.

There have been reports of positive THC metabolite results on immunoassay with nonsteroidal anti-inflammatory drugs (NSAIDS), efavirenz, proton pump inhibitors (PPIs, such as pantoprazole), and hemp-seed food products.6,15Dronabinol, for instance, a cannabinoid indicated in adults for the treatment of: anorexia associated with weight loss in patients with AIDS, and for nausea and vomiting associated with cancer chemotherapy in patients who have failed to respond adequately to conventional antiemetic treatment,is likely to produce positive results on THC immunoassays because this medication consists of synthetic delta-9-tetrahydrocannabinol.16 A true positive result may come as a surprise to a patient using only CBD as it may be assumed to contain less than 0.3% THC. Lastly, the patient may simply be utilizing marijuana or THC products.

Use of THC may or may not be permitted in a provider’s practice. In addition to the presumptive testing conducted, a provider may choose to proceed with definitive (quantitative) testing to determine the true cause of the positive THC result. Quest is developing testing methods for CBD. Providers can always reach out to the lab for assistance in ordering or interpreting testing or results.

Key Takeaways

  • With the explosive growth in THC and CBD use both medicinally and recreationally, as well as evidence suggesting that legalizing marijuana might contribute to a modest reduction in opioid use, clinicians need to familiarize themselves with cannabinoid pharmacology, adverse effects, and monitoring strategies.
  • CBD products may produce positive results on urine drug monitoring tests if the product contains more than the federally legal amount of THC as these products are not regulated by the FDA. 
  • A thorough patient interview and review of concomitant medications can help providers identify potential causes of urine drug tests positive for THC. 
  • Expectations regarding findings of illicit substances or nonprescribed medications should be discussed during the patient’s first visit with their provider.


Written by Courtney Kominek, PharmD, BCPS, CPE and Nicole Burns, PharmDDisclosure: The case presented herein is hypothetical and the views presented do not represent those of the authors’ employers, the VA, or any federal agency.

Last updated on: May 13, 2020
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Scenario: Metabolite Missing on Screen for a Patient on Medication-Assisted Treatment; Possible Adulteration
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