All You Need to Know About False Positives

What is a False Positive Drug Test?

A drug test may result in the presence of an illegal drug even if the individual has not taken any. In such cases, there is a need to have a confirmatory test to prove that the individual is indeed free from any illegal substance abuse.

When an individual is undergoing a drug test, two samples are usually taken so that there would be a confirmatory test to be done later on. It should be noted that drug tests are not 100 percent accurate. If the confirmatory test would give a positive result, complete medical history of the individual should be carefully noted because he might be taking some prescribed medication, vitamins and dietary supplements, or natural herbs that could trigger a false positive result in the drug test.

An additional concern is the possibility of drug test adulteration or cheating. Employees who attempt to disguise their drug abuse can be screened with Urine Drug Test Adulteration Strips, which are easy to use and easier to afford.

It is highly recommended that all positive results be followed up by a second test to confirm the initial result and be able to rule out any false positives. It is best to use another method that is different from the previous screening to avoid the possibility of having another false positive result.

GC/MS is used as the standard confirmatory test. If this test gives a positive result, then it is likely that the result is positive. Using this test would mean additional cost, but it ensures the integrity of the drug testing procedures and results.

The tests are reviewed by a Medical Review Officer (MRO), who is a licensed physician by profession. The MRO undergoes extensive training with regards to federal regulations to drugs and alcohol testing. The primary role of the MRO is to prevent, detect and to control the use of drugs in a workplace to ensure safety and increase in productivity of the employees.

Any positive result on a urine drug test must be verified with a secondary or confirmatory test before it can be used for legal purposes. Not all states in the U.S. have approved of mandatory drug testing among employees, but any company that does drug testing has the right to defend its action in a court of law.

It should be noted that not all individuals tested may have positive results. If an employee gets fired or suffers from any form of an insult as a result of the false positive drug test result, the company may be legally liable and can be subjected to lawsuits for damages.

The Possibility of False Positives

Sometimes, the food that we eat may affect the results of our drug tests as well as a few over-the-counter drugs that we take. Here are some of the most common drugs that may cause false positives in drug tests:


Tested Positive For

Cold remedies


Diet Pills


Hay Fever remedies


Hemp Food Products



Marijuana, Benzodiazepines

Nasal Decongestants


Sleep Aids


Poppy Seeds


Boston Medical Center reviewed earlier studies on drug tests and reported that cold medications and tricyclic antidepressants can produce a false-positive result for amphetamines. The same result was discovered for those who were using the antidepressant Zoloft, wherein it was thought that the individual has benzodiazepine problems. Employers should also note there are certain prescriptions that cause a false THC drug screen.

Let us look at some of the common substances that turn up positive for illegal drugs in some drug tests:

Cold Remedies

One of the core ingredients for cold medicine is pseudoephedrine, a synthetic amphetamine that is also used in making methamphetamine. Its action is to shrink the blood vessels along the nasal passages to aid in proper breathing when an individual has a cold. It is an effective drug to treat such condition, but if the individual undergoes drug testing while under medication, urine tests may show that he is positive for methamphetamine.

Vitamin B Supplements

Taking plant-based products that contain vitamin B12 or riboflavin may lead to cannabis false positives. Some commercially produced riboflavin products come from hempseed oil, which has tetrahydrocannabinol (THC). THC is a psychoactive ingredient of marijuana, and this may turn up in a routine urine drug test.


This is one of the most common over-the-counter drugs that people often take to quickly suppress pain. However, taking this painkiller a day before a drug test may result in a false positive test for benzodiazepines, marijuana or barbiturates. Researchers found out that non-steroidal anti-inflammatory drugs (NSAIDs) can interfere with the components of the enzyme-multiplied immunoassay test (EMIT).

Note, however, that it would take about 1200mg of Ibuprofen before it can be detected in a urine test to cause a false positive result.

Food with Poppy Seeds

You may be a fan of bagels with poppy seeds, but it might be best to skip eating this kind of food at least 3 days before a scheduled drug test. The reason is that poppy seeds have traces of opiates like those found in codeine and opium.

A study tried to investigate the truth about poppy seeds in producing positive results after a urine test. One volunteer was asked to eat 3 poppy seed bagels and the other volunteer was asked to eat poppy seed cake. The test was given 30 minutes after ingestion. Both persons tested positive until after 16 hours of ingestion.

Snack Bars

Weight watchers and health enthusiasts may have long chosen to fill their tummies with snack bars that are advertised to have high protein content. Unfortunately, some manufacturers have incorporated hemp seeds into their products, causing false positives in drug tests for THC.

Energy bars that have been approved in adherence to U.S. Department of Agriculture testing standards should contain a maximum of 0.01 percent THC. It would take you about one whole bag of energy bars before traces of THC can be detected.

Tonic Water

It was found out that tonic water, which is made from quinine, when consumed in large amounts may result in a false positive for opiates. Quinine water was used in the past to individuals who were afflicted with malaria. It was in the form of quinine water that these individuals were treated.

Cross-Reactivity Causing False Positive Results

Here is a list of drug categories that may cause false positive results in drug screening procedures:

  • Analgesics
  • Antibiotics
  • Antidepressants
  • Antihistamines
  • Antipsychotics
  • Decongestants
  • Over-the-counter (OTC) products

Detecting Adulteration in Urine Specimens

For as long as there have been urine drug tests, people have been trying to cheat them. Potential cheaters have a number of methods they use to try and adulterate the sample they give so it is imperative that you know these methods and be able to counteract them accordingly.

Some point-of-contact testing kits have built-in adulteration detection systems of their own but even if using one of these tests, it is worth knowing the various ways of cheating. Adulteration techniques (including the built-in ones) may not completely ensure detection of adulteration in every case by they can alert staff to the most common methods of adulteration, thus enhancing the integrity of your drug testing program.

Water Loading

Water loading, as its name implies, is the attempt to dilute one’s urine by drinking copious amounts of water (or any other fluids).

It is one of the most common adulteration techniques and can be difficult to spot unless the testing technician is experienced in detecting water loaded specimens.

Running a parallel test for creatinine concentration levels (more on that below) is one way of detecting water loading.

Adding Common Household Products to a Sample

Some cheaters prefer to add things to the specimen and will often add whatever they have sitting around their home, such as bleach, cleaning products or peroxide in an attempt to change the chemical make-up of the sample and produce a false negative reading.

In order to add these products to the sample, of course, they must be sneaked into the testing area. That is why it is a good idea to have test subjects empty their pockets and you may also want to frisk them before they are tested to make sure that they aren’t hiding something to add to the sample.

You may also want to consider requiring that a line of sight be kept on the sample container throughout the entire procedure, although this can raise problems of its own like shy bladder or the necessity to make sure that the tester and test subject are of the same gender.

Some household products are relatively easy to spot in a sample. Bleach, for example, gives off a usually pungent and recognizable odor.

Cleaning products such as Drano might make urine less acidic than usual, which can be a tell-tale sign of adulteration. It may also make the sample unusually warm or cause it to bubble.

There are many products on the internet and in some stores like head shops that claim to render a sample negative when added to it. The presence of these products can usually be detected through analysis of nitrite levels if the confirmatory tests are run immediately.

Other adulteration products are continually being developed and marketed, many of which have to be ingested. Scientists, though, are also continually developing adulteration detection methods to combat these products. It should also be noted that many of these consumable adulteration products simply do not work.

Specimen Swapping

Instead of adding something to their sample, a person might just try and submit a sample that isn’t even theirs at all.

To prevent this, you can take similar action as preventing people from adding things to the sample as noted above, like having test subjects empty their pockets, frisking them and requiring that a line of sight be kept on the sample container throughout the entire procedure.

Monitoring the temperature of the sample closely is another way to detect this type of cheating, as recently voided urine will be warmer than urine that has been previously voided and snuck in. 

Use of Diuretics

Diuretics are substances that encourage the body to urinate more frequently than normal and can potentially decrease the retention time for drugs in the system. Some teas, milkshakes, fruit juices and other fluids act as diuretics. Many of these products also require the ingestion of large amounts of water and this could result in diluting the urine enough that the presence of drugs falls below drug testing cutoff levels.

Other Tampering Methods

There are a variety of less common ways of adulterating samples that people will use and many websites and online forums offer advice for cheating drug tests. Although it would be impossible to monitor all of these sites, it might be worth it from time to time to check them out and see what kind of advice for cheating is being given to people. The more you know, the better prepared you’ll be to catch cheaters.

It also must be accepted that despite the most stringent efforts, some adulteration may indeed occur undetected. But careful interpretation of drug test results coupled with some basic anti-cheating measures will go a long way to ensuring adulteration is at least kept to a bare minimum.

Checking for Temperature, Color, and Other Evidence of Tampering

It is important to observe the color, temperature and odor at the initial collection of the sample. For example, Vitamin B1 (sometimes taken by heavy drug users to help rebuild and rebalance their body’s system after years of drug abuse) gives urine a bright yellow hue. An experienced and properly trained drug testing technician can tell that this color is quite different from the color of unadulterated urine, which should be a light to golden yellow, free from foreign materials, and have a slight ammonia odor. Samples that are completely colorless or extremely pale should be suspect because those are signs of water loading.

Samples outside of the 90 to 100 degrees Fahrenheit (32.2 to 37.8 degrees Celsius) temperature range should also arouse suspicion, as this is the average temperature range of freshly voided urine.

Normal urine has a pH of 5 to 8 and specimens above or below this value should be suspect.

Detecting possible water loading can be done through a specific gravity test, which compares the density of a drop of water to the density of a drop of urine. If the weight of the urine is below a certain level, it can indicate that the urine has been diluted. Samples with a specific gravity under 1.003 should be suspect.

Testing the creatinine level can also help to detect water loading. Creatinine is a metabolic product excreted in the urine by the kidneys and its concentration in the urine is affected by fluid intake. If the creatinine level of a urine sample falls below a certain level, it can indicate that the client consumed large quantities of fluids prior to giving the sample. Values of creatinine less than 20 milligrams per deciliter may be an indication of water loading.

Followup analysis should be performed through additional tests for specific gravity, pH levels, creatinine, and nitrates if cheating is suspected.

Additional Tips

A few additional steps to help avert adulteration include requiring:

  • observed monitoring of all sample submission, as previously mentioned;
  • the submission of a minimum amount of urine;
  • set time limits for providing a specimen (e.g., 1 hour or less from the time of test notification to the time of collection) to minimize the possibility of internal dilution;
  • limited access to fluids prior to providing the specimen.

Now that you know what to look for when drug testing, spotting cheaters should be easier. But the best way to ensure minimal adulteration is by having properly trained drug testing technicians.

Drug Tests Missing Out on Oxycodone

The emergence of false positive results has gotten some people in trouble and led them to spend more for a confirmatory test. On the flip side, there is also the possibility of a false negative result. This occurs when a supposedly illegal substance gets pass any drug test.

One example is oxycodone, which has a substantial false negative rate among drug tests. Oxycodone is an opioid drug that has been reported to be associated with high levels of abuse. Unfortunately, some doctors and drug testing companies are unaware that they need to request a special test for the detection of oxycodone for accurate screening.

There are other drug metabolites that standard drug tests miss. Some of these substances include fentanyl, methadone, and Ultram, to name a few. Some reports also revealed that sedatives and hypnotic drugs have also slipped past traditional drug tests.

How To Avoid False Positive Drug Test Results

With the possibility of false-positive results looming, it is important to understand how to prevent this from happening.

If you are taking some drugs for disease cure or treatment, it would be best to declare these substances to the drug testing agent or center administering the procedures.

Remember that some OTC medications may lead to an erroneous result, some of which include dextromethorphan (DXM), pseudoephedrine, naproxen, some weight loss pills, and nasal decongestant inhalers. There are also other medicines used in hospitals for surgical patients that can cause a false positive result for amphetamines. For instance, amoxicillin has been associated with a false positive urine test for cocaine.

There had been several cases involving drug users who intend to manipulate test results by using commercial urine, diluting urine with water or taking other substances to mask the presence of drugs. The latter may be a fairly easy way to bring out a false positive in the result, but confirmatory tests will always be able to make the results certain.

False Negative Drug Test Results

False negatives, on the other hand, occur when results indicate the absence of drugs in the sample even if there is the presence of these in the system of the one being tested. The following are some possible causes of false negative results.

  1. High cut-off levels. Different drug screening kits are set to various cut-off levels, the standard being those set by SAMHSA or NIDA. A high cut-off level may report a negative test result, even if there is a presence of illegal drugs in the sample. 
  2. Excess water. Reports state that the intake of large amounts of water or diuretic liquid such as coffee or tea may yield false positive results.
  3. Adulterants or additives. Some people add different substances (bleach, salt, peroxide) to their urine samples or intake various detoxifying drinks (Naturally Clean, System Flush, Urine Luck) to cheat their drug test.