Can Allergy Medication Cause A Positive Methamphetamine Test?

In our latest question and answer, the pharmacist discusses which allergy medications have been reported to cause false-positives for amphetamine.

Question

I am abruptly cut off from my meds, like Adderall, and I can't focus, concentrate and unthinkable ideas have crossed my mind! I know enough that I should have been tapered off of Adderall, not stopped abruptly. I had a positive test for amphetamine anyway and the only change in my medication has been OTC allergy aids since spring began. I'm simply trying to find out if the allergy meds could have caused a positive result that led to the assumption that I was "abusing" my meds, which has subsequently left me without them. Thank you for your time.

Asked by Turtledove On Jun 21, 2019

Answered by
Medical Content Reviewed By PharmacistAnswers Staff

On Jun 21, 2019
Man Holding Urine Cup In Gloves With Text - Allergy Medications Amphetamine False Positives

Overview

Yes, several over the counter medications used to treat allergies and associated symptoms (e.g. nasal congestion) have been reported to cause 'false-positives' for both methamphetamine and amphetamine on urine drug screenings (i.e. assays).

Urine screenings for 'amphetamines' typically encompass not only amphetamines, like Adderall, but also similar stimulant compounds, including:

As far as urine drug tests go, some can distinguish between methamphetamine and other amphetamines, but the most commonly utilized ones will be fairly non-specific and detect only 'amphetamine'.

This is because most amphetamine-like compounds break down eventually in our bodies to amphetamine. Methamphetamine, for example, has at least 7 metabolites, one of which is amphetamine.


Why Do False-Positives Happen?

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False-positive results on urine drug screenings are relatively common, unfortunately, simply based on how these tests work.

Most urine drug screenings are 'immunoassay' based tests, which utilize antibodies to bind and react to a particular drug. False-positive results occur when an antibody binds to the wrong drug and produces a reaction.

Most often, false-positives occur with drugs that have a similar molecular structure to the compound being tested for, but this isn't always the case.

The incidence rate of false-positives isn't well documented, but case studies and anecdotal reports are too numerous to list. Therefore, it is of importance to be aware of the possibility of them occurring.


Drugs That Can Cause False-Positives For Amphetamines

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Specifically, the following over the counter medications have been reported to cause false-positive for methamphetamine (or amphetamine):

Some of these drugs cause false-positives since they are metabolized to compounds in the body that are structurally related to amphetamine.

For example, selegiline, an antidepressant, is metabolized to l-amphetamine and l-methamphetamine.


Allergy Medications That Can Cause False-Positives For Amphetamines

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Of these medications listed above, the following are commonly used for allergies:

  • Phenylephrine (nasal decongestant)
  • Pseudoephedrine (nasal decongestant)
  • Brompheniramine (antihistamine)
  • Ranitidine (antihistamine H2-antagonist for stomach acid)
  • Phenylpropanolamine
  • Vicks Inhaler (nasal decongestant)

They have all been reported to cause false-positives for amphetamines on urine drug tests. In the next sections, we'll take a look at each.


Nasal Decongestants

The two most commonly used over the counter nasal decongestants are:

  • Pseudoephedrine (Sudafed)
  • Phenylephrine (Sudafed PE)

These nasal decongestants are well-known to cause false-positives for amphetamines on urine drug tests. They are technically classified as 'stimulants' and are structurally similar to amphetamine.

In fact, most studies report that urine drug tests for amphetamine can be the most difficult to interpret due to the high risk of false-positives and the sheer number of potential causative agents.

The following is from one of the most cited studies discussing urine drug screening (Urine Drug Screening: Practical Guide for Clinicians):

"Interpretation of amphetamine assays requires a detailed medication history that includes over-the-counter, prescription, and herbal medications. Pseudoephedrine, ephedrine, phenylephrine, and decongestants common in over-the-counter cold medicines are known to cross-react with the amphetamine assay."

It should be noted that topical nasal decongestants (e.g. sprays) that contain phenylephrine would be very unlikely to cause a false-positive test due to low systemic absorption. Nevertheless, it is still a possibility.

Another often used nasal decongestant is Vick's nasal inhaler. As stated, topical decongestants are unlikely to cause false-positives. however, one of Vick's inhalers contains l-methamphetamine (levomethamphetamine). While it appears to be relatively safe in the sense that it can't be easily abused, consistent use has been reported to cause false-positives on amphetamine urine screens since it is metabolized in the body to l-amphetamine.

Antihistamines

Several antihistamines have been reported in studies to be responsible for false-positive amphetamine screens.

Brompheniramine, one of the active ingredients in Dimetapp, has specifically been singled out.

Brompheniramine is a first-generation antihistamine (H1-blocker), similar to Benadryl (diphenhydramine) and Chlor-Trimeton (chlorpheniramine). One study stated the following:

"As previously reported, products structurally related to amphetamines interfered with the assay reagents and yielded false-positive results. Brompheniramine produced a positive result for amphetamine with I.D."

As it concerns antihistamines for allergies, brompheniramine appears to be the only to watch out for. This is likely because one (or more) of its metabolites is similar in structure to amphetamine.

There have not been reports of other commonly used antihistamines, like Claritin, Zyrtec and Allegra, causing any problems. 

"...the investigators theorized that the metabolites of brompheniramine might have interfered with assay results, producing a false-positive result."

Interestingly, a different type of antihistamine, Zantac (ranitidine) has also been cited numerous times as being one of the most common agents responsible for false-positive amphetamine screens, even though it (nor its metabolites) are structurally similar to amphetamine.

Zantac (ranitidine) is an H2-blocker, used to decrease stomach acid and treat related disorders (e.g. GERD). One study reported the following:

"However, cross-reactivity was reported with a structurally dissimilar agent: ranitidine. Ranitidine use resulted in false-positive results for amphetamine and methamphetamine using monoclonal antibody technology, EMIT d.a.u. (Syva Company, Palo Alto, CA). Ranitidine is available without a prescription (75 and 150 mg) and with a prescription (150 and 300 mg). In a review by the assay manufacturer, the most commonly reported dosage range associated with false-positive reports was 150–300 mg daily."

It appears that, overall, false-positives aren't overly common with Zantac, since only certain tests have reported problems with false-positives and you need to be tested soon after taking a dose (within a few hours) to reach a concentration in the urine thought to elicit a positive result.


Additional Information

If you are scheduled to have a urine drug screen, it is extremely important to let your doctor/tester know about all the medication you are taking. As discussed above, drugs that you think wouldn't have any impact on the test (e.g. Zantac), could potentially influence the results.

If you do, unfortunately, come back with a positive screening that you believe is in error, there are other, confirmatory tests that can be done to rule out other agents.

One of these tests is known as GC-MS (gas chromatography-mass spectrometry). This test doesn't rely on antibodies (like immunoassay urine tests do) and can identify specific compounds in a given sample.


Summary

Several medications used for allergies including antihistamines (e.g. brompheniramine) and nasal decongestants (e.g. pseudoephedrine) could potentially cause false-positive results on amphetamine drug screenings.

References
  1. Urine Drug Screening: Practical Guide for Clinicians. Mayo Clinic Proceedings
  2. Commonly prescribed medications and potential false-positive urine drug screens. American Journal of Health-System Pharmacy
  3. Reduced interference by phenothiazines in amphetamine drug of abuse immunoassays. PubMed
  4. Metabolites of chlorpromazine and brompheniramine may cause false-positive urine amphetamine results with monoclonal EMIT d.a.u. immunoassay. PubMed
  5. Ranitidine cross-reactivity in the EMIT d.a.u. Monoclonal Amphetamine/Methamphetamine Assay. PubMed
  6. Ranitidine interference with the monoclonal EMIT d.a.u. amphetamine/methamphetamine immunoassay. PubMed

About the Pharmacist

Dr. Brian Staiger Pharm.D

Dr. Brian Staiger is a licensed pharmacist in New York State and the founder of PharmacistAnswers.com. He graduated from the University At Buffalo with a Doctor of Pharmacy degree in 2010. He has been featured in numerous publications including the Huffington Post as well as a variety of health and pharmacy-related blogs. Please feel free to reach out to him directly if you have any inquiries or want to connect! He's answered thousands of medication and pharmacy-related questions and he's ready to answer yours! Brian.Staiger@PharmacistAnswers.com Office: 716-389-3076

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