False Positive Drug Screen

False positives on drug screening tests

A false positive drug test occurs when a drug test incorrectly indicates the presence of a substance that is not actually present in the individual's system. Drug screening tests typically detect the presence of specific drugs or their metabolites in bodily fluids such as urine or saliva.

What are the causes of a false positive drug screen?

Several factors can contribute to false positive results, including:

  1. Cross-reactivity: Some substances or medications may cross-react with the tests and produce a positive result. This means that a substance structurally similar to the targeted drug may trigger a positive response.
  2. Medications: Certain over-the-counter or prescription medications can lead to false positives. For example, cold medications, pain relievers, and some antibiotics may interfere with drug tests.
  3. Dietary factors: Some foods and beverages, such as poppy seeds, can cause false positives for certain drugs. Poppy seeds, in particular, contain compounds that are similar to opioids.
  4. Testing errors: Mistakes in the testing process, handling, or labeling of samples can occasionally also result in false positives.

How often do false positive drug tests happen? 

The frequency of false positive drug tests can vary based on several factors, including the specific type of drug test, the substances being tested, the testing methods used, and individual circumstances. Overall, false positives are relatively uncommon, especially when confirmatory lab testing is employed to verify initial positive results. 

While false positives are not extremely common, they are not unheard of. That's why confirmatory testing is crucial in workplace drug screening and healthcare drug testing to rule out false results and ensure accuracy. If someone receives a positive result on an initial drug test, they may request confirmatory testing to provide a more definitive result.

Which types of drug test are more likely to give false positive?

While false positives can occur with any type of drug test, some testing methods may be more prone to false positives due to various factors. Here are a few types of drug tests and considerations:

Urine Drug Tests:

  • Potential for false positives: Urine drug tests are commonly used for drug screening, but they may be more susceptible to false positives due to cross-reactivity with certain medications and substances.
  • Common sources of false positives: Poppy seeds (which can contain trace amounts of opiates), certain over-the-counter medications (such as cold medications), and some antibiotics may contribute to false positives in urine tests.

Saliva Drug Tests:

  • Advantages and disadvantages: Saliva drug tests are less prone to false positives compared to some other tests. However, they may have a shorter detection window than urine or hair tests so the risk of a false negative is much higher.
  • Potential for external contamination: The risk of false positives due to external contamination (e.g., exposure to drugs via secondhand smoke) is generally lower in saliva tests compared to urine tests.

Hair Tests:

  • Long detection window: Hair tests have a longer detection window than urine or saliva tests, but they are less likely to yield false positives.
  • Limited external contamination: Hair drug tests are less susceptible to external contamination, but they may not be entirely immune.

Blood Tests:

  • Specificity: Blood tests are considered more specific than urine tests. However, false positives may still occur, especially if there are issues with sample handling or interference from certain medications.

What medication is most likely to cause a false positive on a urine drug test?

Several medications have the potential to cause a false positive on a urine drug test due to cross-reactivity with the substances targeted by the test. Some common medications known to be associated with false positives in drug tests include:

  1. Poppy Seeds: Consuming products containing poppy seeds can lead to a positive result for opiates. Poppy seeds contain trace amounts of morphine and codeine.
  2. Pain medications : Some over-the-counter and prescription painkillers and anti inflammatory drugs may cause false positives on drug tests. 
  3. Certain antibiotics: Some antibiotics have been reported to cause false positives.
  4. Antidepressants: Some antidepressants may potentially lead to false positives. 
  5. Some cough and cold medications including inhalers may cause false positives. 
  6. Antipsychotics: Certain antipsychotic medications, such as chlorpromazine or quetiapine, may cause false positives for amphetamines or methamphetamines.

If someone is taking medications and is concerned about potential false positives on a drug test, they should inform the testing facility about their medications before the drug test, and, if necessary, request confirmatory laboratory testing to ensure accurate results. Consulting with the drug test provider or a drug testing lab can also provide guidance on managing such situations.

It's important to note that drug tests are designed to be as accurate as possible, but no test is perfect. Confirmatory testing methods, such as gas chromatography-mass spectrometry (GC-MS) with a laboratory are often used during workplace drug screening and healthcare to verify all non negative (ie positive) results and reduce the likelihood of false positives.

Need advice regarding a suspected false positive drug test, we're here to help

If you need any advice regarding the drug tests that we supply or are concerned you may have a false positive, then please contact our UK Drug Testing customer support team for advice. They are available Monday to Friday 8.30am to 5pm by chat, telephone and email.

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