What can cause a false positive on a drug test?

In this article:

• What drug tests detect
• What is a false positive?
• Medications
• Substances
• What to do

In this article

• What drug tests detect
• What is a false positive?
• Medications
• Substances
• What to do

There are several instances where you may be asked to complete a drug test—employers may require one when you’re applying for a new job or if you are a student or an athlete. Urine drug screens are the most common test (although other body fluids may be analyzed). The test, an immunoassay that uses antibodies to detect drugs and their metabolites, is simple and painless and only requires a urine sample. It can feel a little unnerving to be asked to take a drug test, and it is important to know that there are some medications and other substances that could cause a false positive drug test result.

What can drug tests detect?

Drug tests can identify various substances commonly associated with abuse or misuse, including drugs like marijuana (THC), crystal methamphetamine, cocaine, PCP, and heroin. They can also detect prescription medications, such as benzodiazepines, barbiturates, amphetamines, methadone, and opioids.

Drug tests are generally reliable. Still, certain factors, including specific medications, can produce false positive results.

What is a false positive drug test?

A “false positive” result occurs when the analytical drug detection method recognizes some of the molecules in the body as illegal drugs when you haven’t ingested any illegal substances. Drugs that are typically screened for include amphetamines, methamphetamines, benzodiazepines, barbiturates, marijuana, cocaine, PCP, methadone, MDMA, and opioids. Some of the above, such as benzodiazepines, barbiturates, and prescription opioids like oxycodone, fentanyl, and codeine, may be legally or illegally obtained. Other examples, such as cocaine and PCP, are illicit substances.

Research conducted at Boston Medical Center shows that drug tests produce false positives in 5% to 10% of cases. Although this is not a high percentage, the consequences of failing a drug test could jeopardize your career, education, or job prospects. Several common prescriptions, over-the-counter medications, herbs, vitamins, and even some foods could trigger a false positive drug test. According to one study, false positive drug tests are most commonly reported for amphetamine and methamphetamine. That’s because common over-the-counter medications can result in false positives for these substances.

When it comes to prescriptions, “warnings are available, but usually only if you look for them,” says Brent McFadden, Pharm.D., the owner of Brent’s Pharmacy & Diabetes Care in St. George, Utah. “It is usually in the fine print, and most people, in my experience, don’t read the material given to them by the pharmacist.”

Research suggests that 10% to 15% of drug tests yield false negative results. While urine drug tests are most commonly used, their accuracy depends on several factors, including the frequency of drug use and how fast the drug is metabolized by the body. It’s important to note that no drug test is 100% accurate.

13 medications that cause false positive drug tests

So, if you are like most people who don’t take the time to study the fine print, here is a list of prescriptions and over-the-counter medications that could cause a false positive drug test.

1. Analgesics/ NSAIDS

The medication Daypro (oxaprozin), which is prescribed for types of arthritis, may result in a false positive test for benzodiazepines. The pain medication tramadol could trigger a false positive result for PCP. In rare cases, common over-the-counter anti-inflammatory pain medications such as Advil (ibuprofen) and Aleve (naproxen) could make you test positive for barbiturates and THC (marijuana/cannabinoids). Ibuprofen can also make you test positive for PCP.

2. Antibiotics

Quinolone antibiotics are commonly prescribed for certain infections (urinary tract, sinus, etc.). Levofloxacin may trigger a false positive urine result for opiates. Avelox (moxifloxacin) may trigger a false positive for amphetamines. Rifampin, an antibiotic used to treat tuberculosis, can also lead to a false positive result for opiates.

3. Antidepressants

According to research, certain antidepressants can cause false positive drug test results. For example, selective serotonin reuptake inhibitors (SSRIs) like Zoloft (sertraline) and Prozac (fluoxetine) can cause false-positive results for benzodiazepines and lysergic acid diethylamide (LSD) or for LSD and amphetamines, respectively.

 

The antidepressants Wellbutrin (bupropion) and trazodone can cause a false positive result for amphetamines or LSD. A false positive result for PCP can occur in individuals taking the serotonin and norepinephrine reuptake inhibitors (SNRIs), Pristiq (desvenlafaxine), or Effexor XR (venlafaxine).

4. Antihistamines

Antihistamines and some sleep aids containing diphenhydramine (like Benadryl) could cause a false positive result for methadone or, rarely, PCP. Doxylamine (the active ingredient in Unisom) may also trigger a positive drug result for methadone, opiates, and PCP.

5. Central nervous system (CNS) stimulants

Ritalin (methylphenidate) and Adderall are used to treat ADHD and are well known to cause a positive test result for amphetamines and methamphetamines, so tell the lab that you take this medication before your appointment.

6. Cough suppressant

Dextromethorphan, the active ingredient in Robitussin-DM, Delsym, and other over-the-counter and prescription cough suppressants or combination cold and flu products, may cause a drug screen to be positive for opiates or PCP.

RELATED: Learn the dangers of a cough syrup addiction

7. Decongestants

The active ingredient in Sudafed (pseudoephedrine) is also the main ingredient in the illicit making of methamphetamine, also known as crystal meth. Taking Sudafed can result in a false positive for amphetamine or methamphetamine.

8. Proton pump inhibitors

Prilosec (omeprazole), Nexium (esomeprazole), Protonix (pantoprazole), and Prevacid (lansoprazole) are used to treat gastroesophageal reflux disease (GERD) or peptic ulcer disease (PUD) and can cause a false positive for THC.

9. Weight loss pills

The weight loss drug phentermine may produce a false positive drug test. That’s because the chemical structure of phentermine is similar to that of amphetamine, so if you’re taking the drug, it is likely to appear as a positive result on a 5-panel urinalysis.

10. HIV medication

People taking the HIV medication efavirenz may obtain false positive drug test results. In one study, 49 out of 50 patients taking the drug tested positive for benzodiazepines. As well, false positive urine tests for cannabinoids have been reported among those taking efavirenz.

11. Blood pressure medications

Common medications like labetalol, a beta-blocker used to treat hypertension, and Cardizem (diltiazem), a calcium channel blocker used to treat hypertension and chest pain, may result in false positive drug test results for LSD. Labetalol can also cause a false positive for amphetamine or methamphetamine because a labetalol metabolite is structurally similar to amphetamine.

12. Metformin

Metformin is a drug commonly used to reduce the blood sugar of patients with diabetes. The drug has been linked to false-positive drug test results for amphetamine.

13. Prednisone

Prednisone is a corticosteroid that is detectable in your urine, so if you are taking the drug, you may test positive for steroids.

“My recommendation to anyone taking these medicines who might be drug tested is, first and foremost, to be honest with the tester,” says Dr. McFadden. “Know if the meds you are taking might cause a false positive and notify the administrator of the test. If it is prescribed, make sure you have the label from the pharmacy, which will show that the medication was prescribed to you. If it is an OTC product, have some kind of documentation (the container it was in, a note from your physician, etc.) that you have taken it.”

What substances can cause a false positive?

In addition to prescription medications, these other common substances can lead to a false positive drug test.

1. CBD (cannabidiol)

CBD is the non-psychoactive portion of the marijuana plant that has become a very popular remedy for everything from pain control to promoting sleep to helping relieve anxiety. Urine drug testing screens for the presence of THC, the psychoactive component of marijuana, but a problem could arise due to the fact that these products are not very well-regulated, and cross-contamination can occur.

“With CBD available in everything from drink powders to weight loss formulations, to tinctures of all types, false positive urine screenings for THC will become more and more common,” warns Dr. McFadden.

2. Secondhand marijuana smoke

According to research, it’s highly unlikely that secondhand smoke will cause a false positive test for marijuana. In rare cases, a false positive might occur, but it will be most likely within several hours of exposure.

3. Poppy seeds

Can poppy seeds make you fail a drug test? Ingestion in large quantities (such as in a poppy seed bagel or muffin), the tiny black seeds might cause a false positive drug result for opioids. Poppy seeds come from the seedpod of the opium poppy, and while the seeds are cleaned before consumption, they may still contain trace amounts of opium residue. In 1998, the federal government raised the threshold on opiates from 0.3 micrograms to 2 micrograms per milliliter, but some drug testing facilities still go by the old standard (which would increase the likelihood of a false positive result).

4. Mouthwash

Alcohol in hand sanitizer (from heavy or frequent use), certain liquid medications, and mouthwash or other breath-cleaning products containing alcohol could potentially cause you to test positive for drinking alcohol.

5. Tonic water

Tonic water contains quinine, and when consumed in large amounts, could lead to false positive results for illicit drug use.

6. Coca tea

Coca tea is made from coca leaves, which are part of the coca plant from which cocaine is derived. Coca leaves are illegal in the United States, but if you consume the tea in another country like Bolivia or Peru, you may receive a positive test result for cocaine.

Can you fight a false positive drug test?

If you believe you have a failed drug test due to taking a prescription drug or consuming one of these products, you do have options, such as seeking confirmatory testing from a healthcare provider or clinician.

“I would counsel [anyone who received a false-positive test to ask] the administrator to do a more specific test,” says Dr. McFadden, who recommends samples be sent away to labs to have a more specific mass spectroscopy assay done. “Furthermore, if they can prove they are taking a medicine that can produce a false positive (by producing a legitimate prescription), the administrator may schedule another test 30 to 60 days later. If, under their physicians’ approval, the person can be off the medicine for that length of time, a negative test should result.”