May 8, 2019 | By Tim Stoddart

What Causes A False Positive On a Drug Test?


If you received a false positive on a drug test, you’re not alone.

Some common urinalysis screenings a new employer, a treatment center, a professional sporting league, or strictly for your doctor. You know you’re clean, but your drug test came back positive for something – whether that be opioids, amphetamines, benzodiazepines, or barbiturates. So, what’s the deal?

A false positive on a drug test can be catastrophic – for family, friends, and your professional and social life. Consequences can include loss of employment, jail time, exclusion from sports, or even inappropriate medical care. If you’ve received a false positive drug test, a save of shock can fill your mind. While a flood of questions and concerns spring up, there are a number of food items, prescription drugs, and over-the-counter medications that can cause these false positives.

What Causes A False Positive on A Drug Test?

Typically, a false positive on a drug test means that you did test positive for the drug, but in reality – you didn’t take it. Most drug tests are taken by urinalysis, blood sample, or hair follicles, and often times occur when the analytical drug detection method recognizes specific molecules in your body as drugs. When a test neglects to analyze the molecules correctly, it fails to differentiate between the drug molecule and the other structurally similar molecules.

Unfortunately, no drug tests have 100% accuracy, but false positives on a drug test are rare – and studies have suggested that a false positive on a drug test occur in five to 10% of the total cases. It’s important that if you are undergoing testing, you give an accurate history of all prescription, OTC, and dietary supplement medications prior to time of collection so that the person giving the test can be aware of any .

If you’ve received a positive test, it’s crucial to use another test to confirm the false positive, as there are a number of factors that may have triggered the false positive.

Poppy Seeds

There are a number of controlled-exposure studies that have shown as little as one poppy seed muffin, or a poppy seed bagel, or roll (about 15g of seed) can produce detectable amounts of morphine and codeine in a test. In fact, while it is known that poppy seeds do contain opiates, the content does vary depending upon the source of the seed and processing – and certain food processing can lower the opiate levels in the seeds.

In a 2015 study published in the Journal of Analytical Toxicology, researchers detected opiate concentrations in opiate-free volunteers from 15 minutes to 20 hours after consumption of 15 grams of raw poppy seeds. At the time, both 300 and 1,200 ng/mL were evaluated in the urine samples.

Additionally, in November of 1998, federal authorities who mandate drug testing for federal employees raised the required morphine cutoff concentration from 300 to 2,000 ng/mL due to the number of opiate false positives from poppy seed consumption.


In some cases, antidepressants such as sertraline (Zoloft) have caused false positives on a drug test for benzodiazepines or LSD. In a report by Nasky and colleagues, researchers reviewed 522 positive results for drug screens for benzodiazepines while taking sertraline. At the time, they found 26 of 98 records to be false positives. Today, packaging for the drug warns about the possibility of a false positive on a drug test under the testing section.

Quetiapine (Seroquel) which is another antidepressant used to treat bipolar disorder, depression, and schizophrenia may also show up positive for methadone if taken in a large dose.

Other Drugs

Specifically, while poppy seeds and certain antidepressants can cause false positives on drug tests, immunoassay tests, which are used in most instant six to 12-panel urinalysis tests have often been known to pick up false from other types of medications. Some of these can include antihistamines with the ingredients diphenhydramine, dextromethorphan, and ranitidine. Often times, the body metabolizes codeine to morphine and both substances may be found upon testing. Confirmatory testing can distinguish between the products. These can can additionally trigger positive results for methadone, opiates, amphetamines, benzodiazepines, and even PCP (phencyclidine).

Other OTC medications in the class of NSAIDs (ibuprofen and naproxen) have been known to cause false positives for THC. In one controlled exposure study, a study of 60 subjects (510 specimens) concluded that 0.4% of those turned out to be false positives for THC. In one report, authors concluded that acute or chronic use of ibuprofen or chronic use of naproxen were not regularly associated with false-positives but they do recommend secondary testing if needed.

Quinolone drugs are antibiotics typically used to treat a variety of illnesses such as respiratory and urinary tract infections. Some of these include ofloxacin, gatifloxacin, and ciprofloxacin. These medications can often give positive test results for opiates and PCP (phencyclidine).

Check Your Diet and Medications

A false positive on a drug test doesn’t mean that you’re abusing drugs. It does, however, mean that you need to recheck your diet or medication. While a false positive on a drug test can be common, it’s important to be aware of the factors that can cause a positive result. If you have received a false positive on a drug test, it’s best to be honest with the person who is testing you, request a secondary and more comprehensive screening, and if you have the chance beforehand, to stay away from these particular foods and medications.

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