What Can Cause a False Positive Drug Test?

A Person is Answering a Question Related to a False Positive Drug Test Result

You've probably heard about "false positives" when it comes to drug screens. It's an unexpected drug test result that can happen to anyone. In this article, you'll learn what to stay away from before taking a rapid test or a lab screening test.


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What is a false positive?

When employers, labs, etc., use drug tests to examine the presence of illicit and prescription drugs and find them in your body when you haven't consumed them, it's called a false positive. Medications, foods, and other substances can cause false positives. 

A false positive drug test can affect you whether you're looking for a job, playing sports, or going through a drug rehabilitation program. On the other hand, UDS (Urine Drug Screen) tests can help to improve workplace safety, detect drug misuse, track patients' adherence to prescription drugs, and review suspected drug ingestions.

The most common drugs screened when drug testing include:

  • THC (marijuana)
  • Opioids (heroin, opium, morphine, codeine, oxycodone, hydrocodone, and fentanyl)
  • Phencyclidine (PCP)
  • Amphetamines, including methamphetamine, Aderol
  • Cocaine
  • Steroids

Drug testing might also be used for detecting:

Sometimes, a drug test may show the presence of drugs when a person did not take any. Though it is the most common method for initial screening, the disadvantage is the potential for false-positive results.

For example, a rapid urine test for THC  often has a threshold of 50 ng/mL. This may make it less accurate than lab tests for having such a specific threshold amount. Nonetheless, lab errors may result in a false-positive result, as well. 

Rather than the type of test, keeping in mind what foods and medication may help in minimizing false positives

12 things that can cause a false positive on a urine drug screen

Most false-positive test results may be due to things like over-the-counter medicines, drugs, and other foods. Let's go through them below!

Second-hand Marijuana Smoke

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High-school Student Smoking Weed in Front of Her Friends Causing Second Hand Smoking

This can cause a false positive for: THC 

If you spend a lot of time with someone who smokes marijuana, your urine may even have traces of THC. THC is the ingredient found in marijuana that makes you high. However, the chances of you having enough THC to generate a positive result in the federal government's and many private businesses' drug screens are slim to none. This is most likely to occur shortly after being exposed to smoke. Therefore, it would be best to get secondary confirmatory testing if doing a rapid test.

Poppy Seeds

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This can cause a false positive for: Opioids

Morphine and codeine are naturally present in these tiny black seeds. For example, a poppy seed bagel may cause you to test positive for both opioids for up to a day after you eat it. However, keep in mind that this is more likely to happen in labs that still use outdated, lower detection standards for specific chemicals.


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This can cause a false positive for: Ethyl Glucuronide (alcohol tests)

Ethanol, a type of simple grain alcohol, is found in many liquid pharmaceuticals, vanilla extract, and breath-cleaning products. Today, drug tests can identify even trace amounts of alcohol for more extended periods after consumption. If you use anything containing ethyl alcohol, your breath, blood, or urine sample may be checked for symptoms of intoxication in an Ethyl Glucuronide (EtG) test. The presence of EtG in urine is a definitive indicator that alcohol was ingested.

Researchers conducted a study that showed incidental exposure to mouthwash containing 12% ethanol when gargling, according to the manufacturer's instructions, can result in urinary EtG values greater than 50 ng/mL.


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This can cause a false positive for: THC

The hemp plant, cousin of the marijuana-producing Cannabis sativa species, produces cannabidiol (CBD). CBD is a non-psychoactive component of medicinal marijuana used to treat pain and other symptoms. CBD oil, edibles, and other products can contain up to 5% of the mind-altering substance THC in some areas. Your urine may reveal traces of marijuana, depending on when and how much CBD you've ingested.

Coca Tea

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Close Up of Coca Tea Which Can Cause a False Positive Drug Test Result

This can cause a false positive for: Cocaine

In Peru and other parts of South America, this beverage is used as a folk cure. Coca tea is made from leaves of the same plant that produces cocaine. You should stop drinking it a few days before your drug test if you drink it. Coca tea can have a negative impact on your urine drug screening for up to 36 hours after you drink it.


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This can cause a false positive for: Benzodiazepines, Opioids 

Sertraline (Zoloft) is a medication used to treat depression, panic attacks, OCD (obsessive-compulsive disorder), and other mental illnesses. Some urine drug screening tests may not be able to distinguish between sertraline and benzodiazepines. The latter is an older tranquilizer medication frequently discovered in opioid substance abuse in overdose victims. The false positive drug test result may persist for many days after stopping taking your antidepressant.


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This can cause a false positive for: Opiates 

Prescription drugs are unlikely to interfere with your drug tests. However, a few antibiotics have been reported to cause a false positive drug test in rare situations. For example, Rifampicin, a TB treatment, may show up as opiates in some quick urine tests. Furthermore, this study has shown that 18 hours after a single oral dose of 600mg of Rifampicin might give false-positive test results.

OTC (over-the-counter) drugs

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This can cause a false positive for: Methadone, PCP, opiates, amphetamine, LSD, opioids, barbiturates, or THC depending on the medicine.

Some prevalent over-the-counter allergies and sleep meds like Benadryl and Advil PM have diphenhydramine. It can relieve coughs and runny noses. But it can show up as methadone on drug screens, which helps people quit heroin or other opiates and can be addictive. 

In opiate or PCP testing, Tramadol or Ultram may show a false positive. False positives for barbiturates, PCP, or THC may be caused by ibuprofen (Motrin or Advil). Aleve or Naproxen can also cause a false positive for barbiturates of THC. 

Here is a list of more OTCs that can cause false-positive results: 

  • Quinolone antibiotics, such as Levaquin (levofloxacin) or Cipro (ciprofloxacin) used for certain infections (urinary tract, sinus, etc.) have been shown to trigger a false positive urine result for opiates.
  • Doxylamine intoxication can produce false-positive opiate and PCP levels.
  • Brompheniramine use may cause false-positive amphetamine and LSD levels. 
  • Cough suppressant dextromethorphan may give a false-positive result in PCP and opioid levels.
  • Decongestants phenylephrine and pseudoephedrine can show a false-positive result for amphetamine.
  • Pantoprazole has caused false cannabinoid results.
  • Diphenhydramine may also show up as PCP, an illegal hallucinogenic that is one of five types of drugs applicants for all federal and many private-sector jobs are screened for.

HIV Medication

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This can cause a false positive for: THC

Efavirenz (Sustiva) is an antiretroviral medication that aids in the treatment of HIV infection. However, it might appear as if you smoked marijuana on a drug test. Confirmatory tests may be necessary to tell which of the two chemicals is present in your body. You might want to let the lab or clinic know that you're taking efavirenz to avoid any misunderstanding.

Antipsychotic Drugs

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This can cause a false positive for: Methadone, amphetamine, etc., depending on the drug.

Several of these mental-health medicines might cause false-positive testing. Quetiapine, a drug used to treat schizophrenia and bipolar disorder, might cause your urine to test positive for methadone. Another antipsychotic called chlorpromazine can induce amphetamine, a stimulant, to show up on drug tests.

More psychiatric drugs reported causing false-positive tests include the following: clomipramine, amitriptyline, bupropion, trazodone, sertraline, venlafaxine, hydroxyzine, haloperidol, sulpiride, perazine, levomepromazine, aripiprazole, risperidone, amisulpride, quetiapine, lamotrigine, carbamazepine, methylphenidate, and atomoxetine.

Other Prescription Medications

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This can cause a false positive for: Amphetamine, LSD

Medications used to treat hypertension, such as Cardizem (Diltiazem), could lead to a false positive on a urine LSD test. Metformin, a standard prescription for diabetes treatment, has led to some positive results in tests for amphetamine or methamphetamine.

Cardizem (Diltiazem), a medication used to treat hypertension, may give a false positive on a urine LSD test. A commonly prescribed diabetes medication, Metformin, has resulted in some positive amphetamine or methamphetamine tests.

Weight Loss Pills

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Weight Loss Pills Can Cause a False Positive Drug Test Result

This can cause a false positive for: Amphetamines

Phentermine is an appetite suppressant that a doctor usually prescribes. It has a molecular structure comparable to amphetamines, a stimulant used to treat ADHD and as something to help stay awake when studying. If you aren't taking amphetamines for a medicinal purpose, phentermine may cause a false positive on your drug test.

Some things to keep in mind

All medications explained in this article don't make up a complete list of possible false positives. If you know, you'll be obligated to take a pre-employment drug test or any other type of drug test, ask your doctor for more information. Also, inform the medical professional performing the drug screening about any prescription drugs and other foods/supplements you might be taking. 

You can always check before performing lab drug tests with rapid tests like Exploro® THC test strips kit. That might give you a head start in knowing your body's current state of "cleanliness." Let us know what you think in the comments below!



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This is good to know. Had no idea that mouthwash and weight loss pills can cause a false positive. Thank you for sharing. Learned something new today.


I will take note of these when I am required for a drug test. I should avoid these things.

Ramil Hinolan

Very informative, this will help a lot of people to understand the meaning of false positive. Thank you for sharing!

Fransic verso

wow, i’m thankful for your shared post, I didn’t that a weight loss pill can result in false positive.. will advise my friend who’s taking this meds

dorry lyn

I knew about poppy seeds and as someone who schedules drug tests for employment, I have seen that happen. I didn’t know about weight loss pills causing a false positive- good to know.


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