Can a Drug Test Lead to a False Positive?

April 20, 2017



By Anna Jankowska LCPC

Types of Drug Testing

Drug testing is becoming increasingly common during the job application process, as part of random workplace drug testing, and as a condition of probation. Individuals who have not used illicit substances occasionally find themselves subjected to positive drug tests.

Blood, hair, urine, or saliva testing may be requested. Drug testing looks for alcohol as well as certain prescription medications and illegal substances. Amphetamines, barbiturates, benzodiazepines (such as Xanax and Valium), cocaine, designer drugs (bath salts, MDMA, etc.), marijuana, opioids (narcotics including heroin or prescription opiates such as codeine), and PCP (phencyclidine) can all be detected by drug testing.

A common type of drug test is called an immunoassay test. If this test produces a positive result, the laboratory may follow up with a GC-MS (gas chromatography-mass spectrometry) test, which greatly reduces the chances of a false positive.

Can a Drug Test Lead to a False Positive?

False positives on urine drug screenings are uncommon, but no testing method is 100% reliable, and false positives do happen. Some common causes of false positives include:

• Antidepressants

Sertraline (Zoloft) can cause a false positive reading for benzodiazepine. Bupropion (Wellbutrin) can cause a false positive for amphetamines.

• Cold Medicines

Non-prescription or over-the-counter cold, flu, and allergy medications that contain the ingredient pseudoephedrine can cause a drug test to show up as positive for amphetamines.

• Ibuprofen

This over-the-counter pain reliever can cause a drug test to show up as positive for barbiturates, benzodiazepines, and marijuana. 12000 mg of ibuprofen, it is thought, may interfere with the enzyme used in the testing method. Ibuprofen is in a class of pain relievers called NSAIDs (non-steroidal anti-inflammatory drugs). All NSAIDs can cause a false positive. Alternatives to ibuprofen such as aspirin and acetaminophen don’t cause the same effect and are safe to use before a drug screen.

• Poppy seed bagels

This one is so well-known it has even made its way into sitcoms, but just in case you missed it, poppy seeds contain trace amounts of opiates. Eating foods containing poppy seeds have been shown to give false positive drug tests for opiates as much as 16 hours after the seeds were ingested.

• Snack bars

A few brands of granola and snack bars contain hemp seeds for extra protein, which contain very tiny trace amounts of a chemical found in marijuana. Although you won’t get high from eating snack bars, the hemp seeds may cause a false positive drug test for marijuana. You would probably have to ingest a fairly large amount of hemp seeds to get a false positive, but just to be on the safe side, avoid these snack bars before testing.

• Tonic water

Originally developed as a medicine to fight malaria, tonic water contains the substance quinine. Quinine is made from the bark of the cinchona tree, and the bark contains substances that may cause a false positive test for opiates. The amount of tonic water used to make a mixed drink, such as a gin and tonic, is enough to cause a false positive test opiate test.

• Vitamin B Supplements

The B vitamin riboflavin, or B2, is sometimes synthesized from hemp oil. Like hemp seeds, hemp oil contains tiny trace amounts of the chemical found in marijuana and is likewise capable of causing a false positive.

Drug Testing Myths

• Passive marijuana smoke can cause a false positive. This is not a valid reason for a false positive; the amount of marijuana compounds the body ingests from passively breathing marijuana smoke is well below the cut-off level detected by the drug screenings.

• Novocaine can cause a false positive for cocaine. This is also not a valid reason for a false positive since the compounds detected by the test for cocaine are only found in cocaine and not in Novocaine. The “caine” in the two names doesn’t mean the two are chemically similar.

If you are interested in getting urine drug tests, you can get one here:

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  1. I don’t smoke weed nor cigarettes nor any type of drugs at all never have. But I took two Motrin 500 ml. Then took a drug test but failed cause it showed up as thc. I didn’t know that it shows up as a positive result now I’m stuck holding my head trying to think it over and figure it out

    • The same thing happened to to me as a Professional Truck driver I didn’t think it would show a positive result from taking Naproxen, ibuprofen or Motrin for chronic back pain I then waz not ask at the lab was I taking any such medications

    • I’ve tested positive for THC twice in the last few months. I take cbd oil so I thought it was that but just read ibuprofen can do that. I take 800 mg. 2 -3 times a day when my back hurts. Of course no one believes me.

    • My daughter drank 4 energy drinks and took benedryl and had to do a urine sample for her to will it come out positive and if so will they put her back in jail

  2. I took 1200mg of ibuprofen this morning then tested positive for THC around 1pm. I was very upset because it’s been over two years since I’ve smoked. I’m counting on the GC-MS to clear my name.

    • I’m in the same boat bud I drink a monster energy drink before my test I thought the gems test would tell ibuprofen from marijuana but it still came back as positive for marijuana good luck to you and I would like to hear back from you

      • Did they clear up the mishap?

  3. Hi I’m really sick right now so I got some sudeffade to help but am scars to take it because I have a ua Monday and have been told it will come back positive if I do! Can some one Please let me know if it’s safe?? I’m soo sick right now and have tried everything!!

  4. I have had positives lately and I have taken Sudafed since my parents gave it to me for colds and minor Allergys since I was a teen. Looked it up..yes..for amphetamines!! I am 74..retired Nurse.. No drugs I have taken except Sudafed could have caused this! Took one within a few days of last U/A…again!. But now Won’t be able to get pain med I NEED for my back just to function..on them for many years. Frustrating!

    • I am on Metformin and I take ibuprofen or Naproxen and I came up positive in a drug screen how can I prove that I do not do drugs

    • I feel bad for you I’m also on pain meds for chronic pain I do know that you have to let the DR know every drug that you are taking or else they will stop your pain meds I Pray for you to find another Good DR

  5. i did not see any wording about naproxen being safe under the dot rules for the un constitutional drug testing program.
    look for your self in the
    i am a truck driver, and have a bad back from driving for 40 years, as well as a couple “other” injury’s. so am in pain all the time.

  6. What if I i took 500 mg of acetaminophen for my back surgery would it cause a false positive for thc

    • U obviously didn’t read the post.

  7. I take drug screens weekly. I have not smoked pot for several months before my first positive screen and 3 months for the 3rd positive screen.
    My levels were 33 ng, 29 my and 50 ng. The cutoff for a negative screen is 50 ng. Any level above 50 my is considered positive. None of my tests were above 50 by. When a screen is found to be positive it is then sent to a lab with much stricter levels (20 or 15 ng) to confirm positive. Because I have Medicaid all screens are automatically sent to lab regardless of positive or negative. This is not usually the procedure since a confirmation UDS is not meant to be used for the purpose of concluding a positive or negative for THC, simply to confirm the presence of the drug to rule out false positives caused by meds or foods. My social worker said I have 3 positive screens for THC but that is not correct according to the literature. A negative finding does not mean the level has to be 0, just 50 my or below. The confirmation screen cannot be used to ascertain a positive if over the 15 or 20 ng. because the level is so low there is a high possibility of a false positive from CBD oil, help seeds, Ibuprofen or Naproxin or discontinued use of pot which is long enough ago to be considered negative. Am I right in fighting this misinterpretation of the confirmation screen being used as a positive result on my UDS?

  8. How does a person test clean when so many things cause you to test positive no wonder our Jails are so full and for those scram brackets they’re also very bad for false readings my daughter did time when the scram bracelet readings were positive for alcohol and she didn’t drink any alcohol and was very careful of the soaps and creams and the foods she ate I think our system stinks and they set everyone up for failure, It’s all about the MONEY


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