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What Medications Can Cause False Positives on Drug Tests?

You’ve made it through the final round of interviews. Now all you have left to do is complete a drug test. 

Pre-employment drug screenings are the most common method used to test for the presence or absence of drugs in humans. These tests can be a requirement for employment but also for medical issues as well.

Drug tests shouldn’t be a big deal for most, but should you worry if you’re taking a prescription medication?

Many prescriptions and over-the-counter medications aren’t the drugs your employer is looking for in an employment drug screening, but sometimes these medications can trigger what is called a “false positive,” showing up as an illegal, or illicit, drug. Yikes!

Before you go in for your test, read on to learn the drug testing process, what medications (and even foods!) can trigger a false positive and how best to prepare for your test.

Understanding the drug testing process

Employee drug screenings have been standard procedure for decades in many industries, but our ongoing opioid crisis is making it a growing focus for employers and HR professionals across the country. 

Drug testing begins with the collection of a specimen — typically urine, although saliva and hair also may be tested. Once the specimen is collected, it is typically divided in half. One portion is panel tested and the other set aside to use in case of error or contamination or to confirm or challenge a positive result. 

The most common panel test is known as immunoassays. Immunoassay drug screens test for the common classes of drug, including:

  • Amphetamine (methamphetamine)
  • Barbiturates (phenobarbital)
  • Benzodiazepines (including Valium, Xanax and Klonopin)
  • Cannabinoid (THC/marijuana)
  • Cocaine
  • Opiates and opioids (fentanyl, oxycodone, methadone)

What causes a false positive on a drug screen?

Immunoassay tests are inexpensive, quick and effective, but they aren’t fail-safe. Unfortunately, inaccurate results on immunoassay tests can happen. Sometimes this can be due to a mishap or error at a laboratory, but certain medications can cause false positives as well.

“False positives can happen when a test detects a substance that isn’t actually there,” said Georgina Rubal-Peace, PharmD, director of Medication Use Policy at Banner Health in Tucson, AZ. “These imposter substances can be byproducts of prescription or over-the-counter medicines, nutritional supplements and sometimes in certain foods. They may not be illegal, but they inaccurately appear as such.”

Makers of immunoassay tests continually refine the sensitivity of the test panels to reduce the likelihood of false positives but with the growing number of substances – particularly prescription drugs – it may always be an issue with immunoassay testing.

Things that can cause a false positive on a drug test

The following is a list of over-the-counter, prescription medications and foods that have the potential to cause unexpected results:

Amphetamine false positives
  • ADHD (attention deficit hyperactivity disorder) medications like methylphenidate (Ritalin)
  • Antidepressants like bupropion (Wellbutrin), fluoxetine (Prozac) and trazadone (Desyrel)
  • Beta blockers like labetalol (Trandate)
  • Diet pills like phentermine (Adipex-P)
  • Medication to treat nausea and vomiting like phenothiazines (Promethazine)
  • Over-the-counter cold, sinus and nasal decongestants like ephedrine and pseudoephedrine (Sudafed) and Vicks inhaler
Barbiturates
  • Pain medication like ibuprofen (Advil/Motrin) and naproxen sodium (Aleve)
  • Sleep aids like doxylamine (Unisom)
Benzodiazepine
  • Pain medication like ibuprofen
  • Antidepressants like sertraline (Zoloft)
Cannabinoid
  • Cannabidiol (CBD) oil
  • Hemp food products
  • HIV medication like efavirenz (Sustiva)
  • Pain medication like ibuprofen
  • Proton-pump inhibitors, specifically pantoprazole (Protonix), may cause false-positive for THC
  • Some vitamin B supplements that come from hemp seed oil
Cocaine
  • Coca tea
Opioids and opiates
  • Quinoline antibiotics used to treat bacterial infections like levofloxacin (Levaquin) and ofloxacin
  • Anti-psychotic medications like quetiapine (Seroquel)
  • Over-the-counter antihistamines like diphenhydramine (Benadryl)
  • Poppy seeds

Should I stop taking medications or “detox” before a drug test?

Don’t stop taking any medications without prior approval and guidance from your health care provider. As well, avoid any quick-fix remedies or detoxes that “make promises” to help you pass drug tests. Their clams don’t hold up — some can even be harmful.

“Remedies purported as magic detoxes on social media, such as taking niacin before a drug test or goldenseal, an herb in the buttercup family, have not been shown to ‘trick’ a drug test and may cause liver injury in high doses,” Dr. Rubal-Peace said. 

Proof-positive: How to handle your drug test

If you regularly use certain medications, supplements or foods that could potentially trigger a false-positive result, let whoever is performing the test know ahead of time. Be prepared to bring or provide a list to the laboratory. Getting in front of the issue will protect you from a potential false positive.

In most cases, any information you share with the lab won’t be included in the test results. All your potential or current employer will receive is a list of positive and negative results. If your test comes back positive, the lab may be able to confirm the results by running a second test, known as a confirmatory assay or chromatography.

“Chromatography refers to a few techniques including gas chromatography/mass spectrometry or high-performance liquid chromatography,” Dr. Rubal-Peace said. “These are highly sensitive and specific tests which require specialized personnel, more complex instrumentation and a longer turnaround time.”

If you believe your positive drug test might have been a false positive, ask to be tested again. Typically, the employer or health care provider will order this test prior to making any employment or clinical decisions.

Takeaway

Drug screenings can be scary for everyone, especially if you have concerns about your employment.

False-positive results can happen, even with no fault of your own. There are a number of prescription and over-the-counter medications, supplements and foods that can cause a false positive.

Get ahead of your testing, and let the lab know of things you’re taking that could affect your results. And, if you think your test results are inaccurate, talk to the employer or your health care provider and ask for a second test that’s more specific and accurate.

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Pharmacy Safety

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