Can Hydroxyzine Cause A False Positive For A Benzo?

The question of whether or not a particular drug or supplement can cause a false positive on a urine drug screening is a common one and a good one to ask. We're happy to help answer this for you!

How Is Urine Tested For Drugs?

The most commonly utilized drug tests are urine-based immunoassays, which work as follows:

• Antibodies are used to bind to and react with a specified compound (such as a benzodiazepine).
• When an antibody finds the compound it is looking for and binds to it; it produces a reaction. Such reactions are recorded as a 'positive' result.

Unfortunately, commonly used urine-based drug tests have a significant problem with 'cross-reactivity'.

Drugs that are not being tested for can occasionally react with the wrong antibody (i.e. 'cross-react'), resulting in a 'false positive.'

Studies that evaluate drugs associated with producing false-positive results often provide huge lists.

For example, the following have been reported to cause false-positive for opioids alone:

• Delsym (Dextromethorphan)
• Benadryl (Diphenhydramine)
• Poppy seeds
• Levaquin (levofloxacin)
• Cipro (ciprofloxacin)
• Verapamil

As you are concerned with hydroxyzine, let's take a look at that drug and see if it is associated with producing false-positive on drug tests.

What Is hydroxyzine?

A sedating first-generation antihistamine, hydroxyzine is structurally related to meclizine.

It has very similar effects to Benadryl (diphenhydramine), another first-generation antihistamine, but they are technically in different medication classes (hydroxyzine is a 'piperazine' antihistamine while Benadryl is an 'ethanolamine' antihistamine).

It is prescribed for a variety of uses, including for itching, allergies, insomnia and anxiety.

HCL Vs. Pamoate

There are two different salt forms available for hydroxyzine:

• Atarax (hydroxyzine HCl)
• Vistaril (hydroxyzine pamoate)

There is quite a bit of dispute regarding the different effects each salt form has.

It is commonly thought that Atarax is used more for itching and Vistaril is used for anxiety and as a sedative.

While a particular individual may have slightly different effects with one or the other, most sources, including the prescribing information for both drugs, state they have near-identical pharmacokinetic profiles.

The onset of effect for both is about 15 to 60 minutes after taking a dose, and both last around 4 to 6 hours. hydroxyzine pamoate may cause slightly more sedation, however.

Does hydroxyzine Cause False Positives For Benzodiazepines On Drug Tests?

Benzodiazepines are among the most commonly prescribed drugs and are used for a wide variety of indications, including anxiety disorders, insomnia, and as a muscle relaxant.

Drugs in the benzodiazepine class include:

• Alprazolam
• Chlordiazepoxide
• Clonazepam
• Diazepam
• Lorazepam
• Midazolam
• Temazepam
• Triazolam

While useful for a variety of indications and disease states, benzodiazepines can cause physiological dependence and have a risk of abuse and misuse. Therefore, they are often included in drug screening tests.

Although there are reports of several drugs causing false-positives for benzodiazepines on drug tests (e.g., sertraline, oxaprozin), hydroxyzine has not been associated with it.

If you tested positive for a benzodiazepine recently on a urine-based drug test, hydroxyzine likely was not the culprit.

Nevertheless, hydroxyzine has been reported to cause a false positive for another class of drugs, tricyclic antidepressants, or TCAs.

One of the most commonly cited studies on urine drug screening, 'Urine Drug Screening: Practical Guide for Clinicians ', states the following regarding TCA false positives:

Antihistamine agents (eg, cyproheptadine, carbamazepine, cyclobenzaprine, and quetiapine) have often been reported to interfere with the serum immunoassay for TCAs because of their 3-ringed structures. Although structurally dissimilar to TCAs, the antihistamines diphenhydramine, hydroxyzine, and cetirizine (hydroxyzine's metabolite) have also been shown to interfere with serum TCA immunoassay in overdose situations. Unfortunately, these case reports did not test for interference in the urine immunoassay, except for quetiapine and cyclobenzaprine.

How Long Does hydroxyzine Stay In The Urine?

In regard to how long hydroxyzine stays in the urine, that can vary by the individual.

For most, it will be detectable for 3 to 5 days after your last dose.

The half-life of hydroxyzine is between 14 and 25 hours. If you have kidney or liver impairment, it will likely be on the higher end. It generally takes 4 to 5 half-lives for a drug to be considered completely metabolized and eliminated from the body.

Therefore, based on the half-life of 14-25 hours, that translates to roughly 3-5 days.

What To Do If A False-Positive Occurs

If you received a positive result on a urine drug test that you think is an error, hopefully, you are able to retest. The chance of hydroxyzine causing two false-positives in a row is very unlikely.

Additionally, if you have the option and the consequences of a positive test are serious to your life circumstances, you should request more specific testing that does not rely on antibodies.

As mentioned, urine-based drug tests that use the 'immunoassay' method are prone to false-positives. There are a variety of other tests that are more accurate.

The most common type of non-antibody test is gas chromatography with mass spectrometry test. This can identify specific drug compounds in a sample and does not rely on antibody reactions, and therefore, 'cross-reactivity'; is not an issue.

Final Words

Thank you and I hope this answer helped!