Can Your Allergy Medicine Cause A Failed Drug Test?

In our latest question and answer, the pharmacist discusses which allergy medications can cause false-positives on urine drug tests.


I have been taking OTC allergy meds, but have to buy them and give ID when I do. I had a work urine drug screen the other day and it showed positive for amphetamines. How does the allergy medicine break down in the body to do that? I need to prove I am not on anything illegal. I am confused as to how this happened?

Asked by Tink On Sep 14, 2021

Answered by
Medical Content Reviewed By HelloPharmacist Staff

On Sep 14, 2021

Key points

  • Several over-the-counter allergy medications have been reported to cause 'false positive' results on urine drug screenings.
  • Antihistamines reported to cause false-positives include Benadryl (diphenhydramine), brompheniramine, promethazine, Zantac (ranitidine), and doxylamine (one of the active ingredients in NyQuil).
  • Sudafed (pseudoephedrine) has been linked to false-positive results for amphetamine.

Thank you for reaching out to us!

I'm so sorry to hear about the problems you are having with the drug tests being administered by your employer. We are happy to provide some insight for you on what may be happening.

Antihistamines & False-Positives

Several over-the-counter and prescription allergy medications have been reported and documented in studies to be responsible for causing false-positives on urine drug tests. Below is a list of commonly used antihistamines that could potentially cause a failed drug test.


A "first-generation" antihistamine, brompheniramine is one of the active ingredients in Dimetapp. Brompheniramine has the potential to cause a false positive for amphetamines on urine drug screenings.


The active ingredient in Zantac, ranitidine is an H2 blocker, most commonly used for acid reflux. It can also be used as an adjunct treatment for allergies. Ranitidine has been known to cause false positives for amphetamine on drug tests.


A prescription antihistamine commonly used in combination with cough medication in anti-tussive products. Promethazine may cause false positives for amphetamine on drug tests.


The active ingredient in Benadryl, diphenhydramine is one of the most used over-the-counter antihistamines and is used for allergies and as a sleep aid. Studies have shown that diphenhydramine can cause false positives for both opioids and PCP.


One of the active ingredients in NyQuil, doxylamine is a sedating first-generation antihistamine and has been reported to cause false positives for opiates on urine drug tests.

Antihistamine - Decongestant combinations

Any allergy medication that contains a decongestant, such as phenylephrine or pseudoephedrine (generic for Sudafed), can potentially cause a false positive for amphetamine or methamphetamine.

These drugs include:

  • Claritin-D (loratadine; pseudoephedrine)
  • Zyrtec-D (cetirizine; pseudoephedrine)
  • Allegra-D (fexofenadine; pseudoephedrine)

All pseudoephedrine products in the United States require your ID to be available in order to purchase.. Pseudoephedrine is the active ingredient in Sudafed, which is well known to cause false positives for amphetamine-based on its chemical similarity to methamphetamine.

Why Do Antihistamines Cause False Positives On Drug Tests?

False positives on standard urinalysis drug tests are fairly common, unfortunately.

The main problem stems from the detection methods they use.

Most employers/medical offices use simple, urine-based immunoassay tests, which work by utilizing antibodies to react to specific drug compounds.

When a specified drug (i.e. drug being tested for) is present in a test urine sample, an antibody binds to it, producing a reaction that is classified as a positive result.

Unfortunately with these urine tests, there can be a significant problem with 'cross-reactivity'. Drugs that are not being tested for often react with the wrong antibody (i.e. 'cross react'), which results in a "positive" result, although incorrect.

As mentioned above, many antihistamines are known to "cross-react" with the wrong antibodies which lead to false positives.

What To Do If You Receive A False Positive Drug Test

Urine immunoassay drug tests should ideally only be used as an initial screening.

As they are known to cause false positives, positive results should be confirmed or refuted with more accurate tests. More accurate tests actually can identify specific drug compounds in a sample, as opposed to relying on a chemical reaction.

These tests include gas chromatography-mass spectrometry (GC-MS) and high-performance liquid chromatography (HPLC).

These tests do not use antibodies and can accurately determine the exact molecule in question. If you received a 'false positive', these tests will be able to confirm whether or not the offending drug compound is actually present in the tested sample.

Final Words

If you feel your urine drug test result isn't accurate, make sure you disclose all the medications you are taking to the testing facility. They may be able to collaborate the fact you are taking something they have recorded as a drug that can interfere with producing accurate results.

In some cases, you may be able to retake a test if your employer will allow it.

Finally, as discussed in the previous section, there are other, more accurate tests available that could confirm or deny the results of a urine test. They are, however, generally more expensive, take longer, and may not be an option for your with your employer.

Thank you again for reaching out to us and good luck!


  • Commonly prescribed medications and potential false-positive urine drug screens, PubMed
  • Ranitidine Interference with the Monoclonal EMIT d.a.u. Amphetamine/Methamphetamine Immunoassay, Oxford Academic
  • False-Positive Interferences of Common Urine Drug Screen Immunoassays: A Review, Oxford Academic
  • Urine drug screening: a practical guide for clinicians, PubMed

About the Pharmacist

Dr. Brian Staiger, PharmD

Dr. Brian has been practicing pharmacy for over 11 years and has wide-ranging experiences in many different areas of the profession. From retail, clinical and administrative responsibilities, he's your knowledgeable and go-to source for all your pharmacy and medication related questions!

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