The Truth About False Positive Drug Test Results
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The Truth About False Positive Drug Test Results

false positive drug test
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Many criminal activities have been associated with the use of illegal drugs. Rampant trading among party goers and even in the streets is increasing at an alarming rate.

In recent weeks, the deaths of a number of individuals who died were associated with carfentanil intake. Carfentanil is designed as a tranquilizer for large animals. However, it is now being sold disguised as heroin to increase its potency.

Drug laboratories are clandestinely operating in some parts of Mexico. It is believed that the source could be coming from China. The Drug Enforcement Agency (DEA) is the leading agency responsible for the regulation of controlled substances in the US.

Apart from carfentanil, there is still a wide market for several other drugs like cocaine, methamphetamine, fentanyl, marijuana and heroin. These drugs are all under Schedule II, which is composed of drugs with a high potential for abuse and may lead to severe psychological or physical dependence with regular use.

With the proliferation of drugs, several companies have required all of their employees to undergo drug testing to ensure that each employee works in a safe and productive environment. Although a lot of controversy is swirling around mandatory drug testing, its importance should never be overlooked.

The effect of drugs varies in every individual and this may be affected by:

  • Frequency of use
  • Mode of using drugs (inhalation, smoked, injected)
  • Amount of Drugs used
  • Potency of drugs
  • Combination of drugs
  • Tolerance to the drug
  • Gender and Age
  • Over-all health and wellbeing
  • Metabolism

Drug Testing Defined

Drug testing is an analysis done to a specimen to look for traces of illegal substances or alcohol. The procedure determines whether an individual is currently using drugs or has used drugs.

Here are the most common methods of drug testing used:


This is perhaps the most common way of testing drugs. This technique is used to determine the presence of opiates, marijuana, cocaine, methamphetamine or benzodiazepines. The test is done by asking the individual to provide a urine sample (taken midstream) to be placed in a specimen cup.

Typical urine drug tests fall on either of these two types:

  • Immunoassay: This type costs less and provides quick results.
  • Gas Chromatography/Mass Spectrometry (GC/MS): This type of test is more expensive, and the results take more time than immunoassay. However, this kind of urine drug screen is used when a specimen resulted to a false positive, leading it to become known as a confirmatory test. This type of urine drug screen rarely produces false negatives.

Drug Test Detection Times in Urine Test

Here are some of the most commonly abused drugs and metabolites, and how long they stay in the urine:

Substance Duration
Marijuana - single use 1-7+ days
Marijuana – regular use 7-100 days
Amphetamines 1-3 days
Cocaine 1-3 days
Heroin 1-4 days
Opiates 1-4 days
PCP 3-7 days

Limitations of urine drug testing

Despite the popularity of urine drug tests, it does not come without limitations:

  • The test may not be able to differentiate between naturally-occurring opioids found in the body or opiate abuse.
  • The amount of drugs present may not be determined.
  • Most substances taken more than a week before drug testing will leave no traces in the urine specimen.


This is a minimally invasive form of drug testing as it would only require a strand of hair to be tested. It is used to detect cocaine, marijuana, amphetamines, PCP and opiates. Drug testing using hair follicles can determine presence of drugs long after it has been used. Coloring of hair will not alter the results of the drug test.

Drug Detection Times in Hair Testing

The following table lists down the detection time of some of the popular drugs in hair samples:

Substance Duration
Marijuana– single use Doubtful
Marijuana – regular use Months
Amphetamines Months
Cocaine Months
Heroin Months
Opiates Months
PCP Months


This type of test can provide more information on drugs and their metabolites compared to urine or hair testing.

Drug Detection Times in Blood Testing

Drug components in blood stay in the samples for the duration of time listed in the following table:

Substance Duration
Marijuana – single use 12-24 hours
Marijuana – regular use 2-7 days
Amphetamines 24 hours
Cocaine 1-3 days
Heroin 1-3 days
Opiates 1-3 days
PCP 1-3 days


This type of drug testing is conducted by swabbing the inner check with the use of a saliva test strip to determine traces of drugs that remain in the oral cavity. The color of the strip will change to a specific color band that is identified to a particular drug.

This test is done to detect presence of opiates, marijuana, cocaine, methamphetamine and phencyclidine. No change in color means the absence of drug.

Detection Times in Saliva Test

Substance Duration
Alcohol From time of consumption up to 12 hours
Cannabis From a few minutes after ingestion to a day
Cocaine From a few minutes after ingestion to a day
PCP From a few minutes after ingestion up to 3 days
Opiates From a few minutes after ingestion up to 3 days
Benzodiazepines Undetermined
Amphetamines From a few minutes to 3 days of consumption
Methamphetamine From half an hours after ingestion up to 3 days
employment verification
Employment Verification - Background Screening

Drug Testing in the Workplace

This issue has been a source of confusion and controversy among employers who want to have their applicants and employees subjected to a mandatory drug test, in order to ensure a safe workplace and to make employees more productive at work. However, this motion has been met with stern criticism and negative feedback from many sectors of society on the basis of violation of rights.

The reality is that it’s highly possible for a number of people in the workplace to be hooked in illegal drugs. While they may think that they pose no harm to fellow employees, problems may arise when workplace accidents happen.

To prevent such incidents, employers would want to conduct random drug testing among employees so that they can be free from any liabilities in the future.

Handling Drug Test Results

A drug test may result to 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.

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 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:

Over-The-Counter-Drugs Tested Positive For
Cold remedies Amphetamine
Diet Pills Amphetamine
Hay Fever remedies Amphetamine
Hemp Food Products Marijuana
Ibuprofen Marijuana, Benzodiazepines
Nasal Decongestants Amphetamine
Sleep Aids Barbiturates
Poppy Seeds Opiates/Morphine

Boston Medical Center reviewed earlier studies on drug tests, and reported that cold medications and tricyclic antidepressants can produce a false-positive result for amphetamine. The same result was discovered for those who were using the antidepressant Zoloft, wherein it was thought that the individual has benzodiazepine problems.

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 a false-positive result. 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 to 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 in 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 to 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.

Drug Classes Associated with 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
  • Certain over-the-counter (OTC) products

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 for 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, 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 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.


Drug addiction alters how the brain should function. With prolonged use, these illicit substances affect not only the individual addicted to them, but also the surrounding community as a whole.

The availability of drug tests makes it easier to pinpoint who among the people around us may be suffering from drug abuse. One way to help these people may be through intervention so that they can be able to get back to their normal lives again. Another way is to make sure that the integrity of drug test results is maintained.

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"Thank you for checking in. The drug tests that we purchased have proven themselves to be an invaluable tool. We recently had to hire temporary workers to help do basic cleaning at our plant, and thanks to the "on-site" capability of screening, we were able save ourselves from some potential hazards.Thank you so much!Nicole" (Nicole)