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Drug Testing FAQs

Medically reviewed by L. Anderson, PharmD Last updated on Sep 5, 2019.

Facts | Types of tests | Workplace testing | Drug detection times | How long to get results? | False positives | More resources

Drug Testing Facts

Drug testing is the evaluation of urine, blood or another type of biological sample to determine if the subject has been using the drug or drugs in question. There are many circumstances that may require drug testing:

  • Pre-employment drug screening test or random, work-related drug testing to identify on-the-job drug abuse.
  • College or professional athletic drug testing.
  • Post-accident drug testing - a vehicular or on-the-job accident which may have involved human error and resulted in casualties or property damage.
  • Safety-related drug testing - if an employee's job could lead to safety issues if judgement or physical ability were impaired.

Drug testing is often done when applying for employment, especially for positions that may involve federal transportation, airline industries and pilots, bus drivers, trucker drivers, railways, hospitals, and other workplaces where public safety is of the utmost importance. However, workplace drug testing is now common in general for many U.S. employers to lessen the impact from drug abuse, safety concerns, and low productivity in the workplace.

Prescription drug abuse is a serious problem in the U.S. The Surgeon General, as reported by NIDA, states that alcohol and drug abuse, including tobacco, costs the economy over $740 billion per year. Costs are related to crime, lost work productivity and health care.

The rate of positive pre-employment workforce drug screens in the general U.S. population hit a fourteen-year high in 2018, according to a new 2019 analysis from Quest Diagnostics.

  • Looking at data from close to 9 million urine drug tests from January to December 2018, the overall rate of positivity increased from 4.2% to 4.4% of samples. This is nearly a 5% increase and the highest level since 2004.
  • The rate of positive tests from opiates has dropped, from 0.39% in 2017 to 0.31% in 2018, a 21% decrease.
  • Results from marijuana (THC) testing continue to rise: in the general U.S. workforce, positive results from 2017 to 2018 have gone up from 2.6% to 2.8% of samples, a greater than 7% increase.
  • Positive results resulting from post-accident testing have also risen: from 7.7% in 2017 to 8.4% in 2018.

A pre-employment drug test is primarily limited to drugs with the potential for abuse, including some prescription drugs, and alcohol. In addition, sports drug testing may be required for college-level, professional and Olympic athletes. Illegal recreational drugs, performance-enhancing drugs such as

may also be required in sports testing.

Pre-employment workplace drug testing usually requires the applicant to give a urine sample, but may also infrequently require blood, saliva, sweat, or hair.

In certain jobs, especially those that require a high level of safety, employees may be subject to random drug testing, as well. Random drug screening may be used in instances of workplace accidents, and if the employer has suspicion that the employee is abusing drugs. Random drug testing may occur without cause for suspicion depending upon company policy. States may have laws regarding random drug testing.

Some U.S. companies may offer employee-assistance programs to support substance-abuse treatment, but many employers are not tolerant of this issue and it may result in termination from employment.

What types of laboratory tests are used for drug testing?

It is important to be sure that the drug testing occurs at a reputable and certified laboratory. Any credible drug screening program will involve a two-step process.

  • Initial (immunoassay) and confirmatory (gas chromatography-mass spectrometry [GC-MS] test) are the methods most commonly utilized to test for drugs.
  • Using a combination of both tests allows a high level of sensitivity and specificity, meaning there is an extremely low chance for false positives or false negatives.

The immunoassay is performed first and is often used as a screening method. If the immunoassay is negative, no further action is required, and the results are reported as negative. If the sample is non-negative, an additional confirmatory GC-MS analysis is performed on a separate portion the biological sample. The more specific GC/MS is used as a confirmatory test to identify individual drug substances or metabolites and quantify the amount of the substance. Confirmatory tests, such as GC-MS should be utilized prior to reporting positive drug test results to employers.

Urine drug testing

Urine is the most common sample type used for drug testing by employers. A urinalysis will show the presence of a drug in the system after the drug effects have worn off; however, the length of time varies by drug. Urine is the only sample type approved for testing of the federally mandated, safety-sensitive workforce.

Typical urine drug tests for employment purposes usually screen for 5 to 10 drugs. Urine screening may detect amphetamines or methamphetamines, barbiturates, benzodiazepines, cocaine, marijuana, MDA-analogues (MDA or MDMA), opiates (codeine, morphine, 6-acetylmorphine [indicative of heroin use], hydromorphone, hydrocodone, oxymorphone, oxycodone), nicotine, or alcohol.

Saliva drug testing

After urine drug screening, oral fluid (saliva) testing is the most common method to test for drug use. It may be referred to as a mouth swab test, and used if an employer or other tester is interested in knowing about recent drug use. It is not ideal to survey long-term use of drugs. Most saliva drug tests can detect usage within a few hours up to 2 days. The donor should avoid any food or beverages for at least 10 minutes prior to the sample being collected.

Saliva is an easy lab test to gather samples, is less susceptible to adulteration or substitution, and can be tested for alcohol, barbiturates, benzodiazepines, cocaine, ecstasy, marijuana (THC), opiates, amphetamines, phencyclidine (PCP), and methamphetamines. It is suitable for all testing reasons, including pre-employment testing, random and post-accident testing.

Blood drug testing

A blood drug test may be used to determine amounts of drug in an employees system at that very moment, usually from minutes to hours. It allows an employer or law enforcement official to determine if a person is actively under the influence of drugs or alcohol. A variety of drugs can be tested for in blood: examples include alcoho, amphetamines, cocaine, fentanyl, marijuana, methamphetamines, opiates, phencyclidine, nicotine, and tramadol.

Blood testing is invasive, requiring a needle stick, but there is little chance for adulteration. Blood testing may be performed in the emergency room for toxicology testing, as well. However, blood analysis often has a short period of detection, as many illicit drugs are metabolized quickly and eliminated from the body. Drugs in urine can usually be detected in a one to three day time period. 

Hair drug testing

Hair testing may be used to determine drug use over the longer term, usually over a 90-day period of time. Hair can be tested for cocaine, marijuana and THC, cocaine, opiates, amphetamine and methamphetamine, ecstasy, phencyclidine, and alcohol. In general, hair testing allows the longest time frame to detect drugs of abuse.

The collector usually takes a 100 gram sample of hair (100 to 120 strands) cut close to the scalp. This method lessens the risk for hair adulteration or substitution, as the sample is collected in full view of the lab personnel.

Rapid tests

Rapid screening can allow detection of drugs that might metabolize quickly and not be detectable at a later screening. Screening for most drugs of abuse and alcohol can be performed. Rapid tests can be performed at an employers workplace or at a local, specified laboratory clinic. A breath alcohol confirmation may be required for a positive screen for alcohol with the instant test.

Rapid tests often utilize urine or saliva for testing. One advantage to rapid tests is that they provide a screening result within 4 hours on average. Any specimens that screen positive would still require a confirmatory test. Confirmatory test results are typically available in 2 to 3 days.

What happens during workplace drug testing?

An applicant is notified that pre-employment drug testing will need to take place as part of the application process. They may have to present to the laboratory within a specified time frame, for example within 24 hours, to lessen the chance that drugs in their system will be excreted and undetectable. Applicants are directed to a specific laboratory to submit a sample for drug screening (usually for urine test results).

Once at the facility, the applicant must submit a sample at the discretion of the laboratory personnel and in keeping with their standard policies. Hair, sweat, saliva or blood drug test samples may also be used in pre-employment drug screen, although this is not common practice.

During the laboratory evaluation, strict chain-of-custody practices and standards are followed to prevent adulteration of the sample. This legal procedure requires documentation of each person who handles the specimen through the entire phase of testing.

Certain laboratory procedures may require direct visual observation while the specimen is being voided, although this is not common. This occurs most often when the donor has previously attempted to tamper with a sample.

5 Panel Drug Test

Employers may use a standard five-panel test of "street drugs" that may include any of the following substances:

10 Panel Drug Test

Some employers may elect a ten-panel drug test that also includes any of the above plus:

Alcohol drug testing may also occur. Other more recent designer drugs of abuse may be included. Which drug test is used is dependent upon the private employer, federal or state requirements, or other workplace guidelines that may be in place.

Who are the companies that perform drug testing?

  • Laboratory Corp of America Holdings (LabCorp)
  • Quest Diagnostics Inc.
  • National Toxicology Labs, Inc.
  • Phamatech, Inc.

Other companies that are used for federal workplace drug testing can be found by state at SAMHSA.gov.

How long do drugs stay in your system?

Many variables may affect the amount of time that a drug remains detectable in the urine or other biological samples, including:

  • a drug's half-life
  • subject's state of hydration and fluid balance
  • frequency of drug use
  • route of administration
  • cut-off concentration used by the testing lab to detect the drug.

General guidelines are available for detection times. Many drugs stay in the system from 2 to 4 days, although chronic use of marijuana can stay in the system for 3 to 4 weeks or even longer after the last use. Drugs with a long half-life, such as diazepam, may also stay in the system for a prolonged period of time.  

Drug Test Chart and Drug Detection Times*

Drug Class Street Name Prescription Brand Name Examples Detection Time in Urine
Amphetamine Stimulant speed Dexedrine, Benzedrine up to 2 days
Barbiturates depressants / sedatives / hypnotics downers, barbs, reds Amytal, Fiorinal, Nembutal, Donna

short-acting:  2 days

long-acting: 1-3 weeks

(based on half-life)
Benzodiazepines depressants / sedatives / hypnotics bennies Valium, Ativan, Xanax, Serax

therapeutic dose: 3 days


chronic use: 4 to 6 weeks or longer

Cocaine

(benzoyl ecgonine metabolite)

Stimulant coke, crack, rock cocaine N/A cocaine urine test: up to 4 days
Codeine Analgesic / Opiate N/A N/A 2 days
Ethyl alcohol, ethanol depressants / sedatives / hypnotics alcohol, liquor, beer, wine, booze N/A

urine: 1 to 12 hours

serum/plasma: 1 to 12 hours

Heroin Analgesic / Opiate smack, tar, chasing the tiger N/A 2 days
Marijuana, Can-
nabinoids
Hallucinogen pot, dope, weed, hash, hemp Marinol, Cesamet

single use: 2 to 7 days

prolonged, chronic use: 1 to 2 months or longer

Methadone Analgesic / Opiate fizzies Dolophine 3 days
Methamphetamine Stimulant speed, ice, crystal, crank Desoxyn, Methedrine up to 2 days
Methaqualone depressants / sedatives / hypnotics ludes, disco bisquits, 714, lemmons Quaalude (withdrawn from U.S. market) up to 14 days
MDMA (methylenedioxy-
methamphetamine)
Stimulant ecstacy, XTC, ADAM, lover's speed N/A up to 2 days
Morphine Analgesic / Opiate N/A Duramorph, Roxanol 2 days
Phencyclidine Hallucinogen PCP, angel dust N/A 14 days, but up to 30 days in chronic users
Propoxyphene Analgesic / Opiate N/A Darvocet, Darvon (all forms of propoxyphene withdrawn from U.S. market in November 2010) 6 hours to 2 days

*Note: This table should be used as a general guideline only. Many variables may affect the amount of time that a drug remains detectable in the urine or other biological samples. Table adapted from LabCorp / Drugs of Abuse Reference Guide.

How long does alcohol stay in urine?

Some employees may ask does alcohol show up on a drug test? Alcohol has a short half-life in the urine. A urine drug test for alcohol may detect alcohol for 2 to 12 hours.

How long does it take to get drug test results?

Results from workplace drug testing are fairly quick and can usually be received in a few days. An employer may also request to have the test done with a rapid test that can provide results on the same day. Negative results are usually received within 24 hours; however, a non-negative screen will require further testing that may take a few days up to one week.

If the initial screen is negative, a medical review officer (MRO) will typically contact the employer with the results. If a positive result occurs, a MRO will contact the applicant for further questioning. It is important to notify the laboratory or MRO of any medications currently in use, including prescription, over-the-counter or herbal medications. The applicant may have to provide proof of a valid prescription and prescriber information for prescription medications.

Can a workplace drug test be false positive or false negative?

A concern for anyone undergoing drug testing is the possibility of a false positive result. Initial screening drugs tests may infrequently result in false positive results, although confirmatory (GC-MS) testing greatly lessens the chances of a false positive - reducing the risk to close to zero.

It is important that a person undergoing drug testing complete an accurate history of all prescription, OTC, and herbal drug use prior to the time of the sample collection. Certain substances, over-the-counter (OTC) or prescription drugs may result in false positives due to cross-reactivity with other substances, although many assays have been reformulated to avoid these possibilities.

Do poppy seeds cause a false positive drug test?

Poppy seeds and dextromethorphan have been reported to lead to a false positive result for opiates. Decongestants (ephedrine) have been implicated in causing false positives for amphetamines. The body metabolizes codeine to morphine and both substances may be found upon testing.

What can cause a false positive for cocaine?

If benzoylecgonine, the main metabolite of cocaine is detected, the person cannot claim that the result is a false positive due to Novocaine or any other "-caine" type of drug. Benzoylecgonine is only found in nature as a metabolite of cocaine, and there would be no other valid reason for it to be present in a drug screen. As previously mentioned, confirmatory testing with GC-MS will identify individual drugs or metabolites in a sample, and almost eliminate the chance for a false positive result. (Doering, et al)

Does passive smoke inhalation cause a false positive for marijuana?

"Passive" smoke inhalation from being in a room with people smoking marijuana is not considered valid, as the cut-off concentrations for lab analysis are set well above that which might occur for passive inhalation.

Other abnormalities in the urine screen may indicate that results may be a false negative or that there was deliberate adulteration of the sample. For example:

  • a low creatinine lab value can indicate that a urine sample was tampered with; either the subject diluted their urine by consuming excessive water just prior to testing, or water was added to the urine sample.
  • creatinine levels are often used in conjunction with specific gravity to determine if samples have been diluted. To help avoid this problem, the testing lab may color the water in their toilet blue to prevent the sample being diluted with water from the toilet.
  • subjects may also attempt to add certain enzymes to the urine sample to affect stability, but this often changes the pH, which is also tested.

All of these variables, and others, are looked at in the lab analysis.

In some labs, patients who receive a positive result may have the option to pay for an independent retest of the urine sample that was originally submitted. A new urine sample is not allowed for the retest as the drug in question may have been excreted from the body by that time.

The results of drug testing should remain confidential and kept separate from the regular employee work file.

Will CDB (cannabidiol) Make Me Test Positive for Marijuana?

Cannabidiol (CBD), one of the components found in cannabis, has been more frequently used in the U.S. since the government lifted a restriction on growing hemp. Licensed farmers can now grow hemp, as long as it contains less than 0.3% THC. Hemp is a cannabis plant that has little tetrahydrocannabinol (THC) in its make-up. THC is the chemical in marijuana that leads to the "high".

CBD is promoted to help with conditions like pain, insomnia, and anxiety. Today, you can find CBD in everything from massage oil extracts, to skin lotions, to gummy bears, and it is easily accessible online or at stores. It is also the primary ingredient in the prescription medication Epidiolex, used to treat seizures in people with Lennox-Gastaut syndrome or Dravet syndrome. 

People who are using CBD may wonder if it can affect their drug test? Researchers have found that pure CBD did not cause a false-positive on two commercial drug tests used in the U.S. However, because these products are not regulated by the FDA, they may not always be pure, which could lead to variable results. A recent study found that 20% of CBD products (1 in 5) were contaminated with THC. Another cannabis compound known as cannabinol (CBN) did react with the drug tests, as it is a tetrahydrocannabinol (THC) derivative.

Bottom line: even if your drug test turned up a false-positive for CBD, a confirmatory test would be used to distinguish CBD from other compounds. However, if your CBD product was contaminated with THC, your confirmatory test may have a positive result. 

Can Employers Drug Test in States Where Marijuana Is Legal?

Yes. Legal rules vary from state to state where marijuana is now legal for recreational or medical use. Also, as marijuana stays in the system over a prolonged period of time, the employee may use marijuana legally, but be drug tested at a later time and lose their job.

In general, marijuana legalization laws in states where it is legal support employers in drug testing for marijuana use and firing people for it. Marijuana use is still illegal under federal law, and many employers prefer to maintain their drug-free workplace policies. However, laws are changing, and some states such as Maine, Arizona, and Minnesota have enacted employee protections. As each state has their own set of laws, it's usually best to seek legal advice to discuss specific marijuana testing laws prior to employment.

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Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

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