Drug Testing FAQs
On this page:
- What is drug testing?
- What types of laboratory tests are used for drug testing?
- What happens during workplace drug testing?
- How long can drugs be detected in the body with a drug test?
- How long does it take get workplace drug testing results?
- What are the chances that a workplace drug test will result in a false positive or a false negative?
Drug testing is the evaluation of a urine, blood or other type of biological sample to determine if the subject has been using the drug or drugs in question. There are many circumstances that may lead to drug testing:
- Pre-employment or random, work-related drug testing to identify on-the-job drug abuse
- Drug testing for college or professional athletes
- 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 - 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, railways, 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 and lower productivity in the workplace.1 The Surgeon General reported that alcohol and drug abuse, including tobacco costs the economy $524 billion per year.2 In 1997, it was reported that 5.4 percent of all workers tested positive for illicit drug use. Many companies may also offer employee-assistance programs to support substance-abuse treatment.
Workplace drug screening is primarily limited to drugs with the potential for abuse, including some prescription drugs, and alcohol. Prescription drug abuse has been reported as a growing problem in the U.S.3 Sports drug testing may be required for college-level and professional athletes. Illegal recreational drugs, performance-enhancing drugs such as anabolic steroids, erythropoietin, diuretics, recombinant human growth factors, alcohol or other drugs may be required in sports testing.
Pre-employment workplace drug testing usually requires that the applicant 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 screening, 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.
It is important to be sure that the drug testing occurs at a reputable and certified laboratory.1 Any credible drug screening program will involve a two-step process. Initial (immunoassay) and confirmatory (gas chromatography-mass spectrometry [GC-MS]) testing 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.4
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 positive, 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.4,5
An applicant is notified that pre-employment workplace drug testing will need to take place as part of the application process, and 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 urine). 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, blood, sweat, or saliva samples may also be used in pre-employment drug screening, 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.3
Employers may use a standard five-panel test of "street drugs" that includes marijuana (THC), cocaine, PCP, opiates (e.g., codeine, morphine) and amphetamines (e.g., methamphetamine). Some employers may elect a nine- or ten-panel drug test that also includes various prescription drugs, such as oxycodone, benzodiazepines, barbiturates, or propoxyphene. Alcohol may also be screened for in the sample. Other more recent drugs of abuse, such as MDMA (ecstacy) may be included. Which drug test is used is dependent upon the private employer, federal requirements, or other workplace guidelines that may be in place.
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, the subject's state of hydration and fluid balance, frequency of use, route of administration, cut-off concentration used by the testing lab to detect the drug, and many other variables. Each person and circumstance is different, and the best way to avoid detection of an abusable drug is to not use 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. Drugs can be detected in hair samples up to six months, although urine samples are used for most workplace drug screening tests. Examples of drugs that can be detected in hair-testing include alcohol, marijuana, cocaine, and amphetamines.
|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: 4-6 weeks or longer
|Cocaine (benzoyl ecgonine metabolite)||Stimulant||coke, crack, rock cocaine||N/A||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: 2 to 12 hours
serum/plasma: 1 to 12 hours
|Heroin||Analgesic / Opiate||smack, tar, chasing the tiger||N/A||2 days|
|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||Desosyn, Methedrine||Up to 2 days|
|Methaqualone||depressants / sedatives / hypnotics||ludes, disco bisquits, 714, lemmons||Quaalude (off U.S. market)||Up to 14 days|
|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||8-14 days, but up to 30 days in chronic users|
|Propoxyphene||Analgesic / Opiate||N/A||Darvocet, Darvon (all form of propoxyphene withdrawn from US 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, including a drug's half-life, the subject's state of hydration and fluid balance, frequency of use, route of administration, cut-off concentration used by the testing lab to detect the drug, or other variables.
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 positive 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 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 for prescription medications.
What are the chances that a workplace drug test will result in a false positive or a 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.4
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. For example, poppy seeds and dextromethorphan have been reported to lead to a false positive result for opiates, and 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. On the other hand, if benzoylecgonine, the main metabolite of cocaine is detected, the subject cannot claim that the result is a false positive due to Novocaine administration, or any other "-canine" drug. Benzoylecgonine is only found in nature as a metabolite of cocaine, and there would no other valid reason for it to be present in a drug screen.4 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.
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. The argument of inhalation of "passive" smoke from being in a room with people smoking marijuana is not valid, as the cut-off concentrations for lab analysis are set well above that which might occur for passive inhalation. All of these variables, and others, are looked at in the lab analysis, keeping one step ahead of those that attempt to foil drug tests.
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.
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- Commonly Abused Drugs and Substances
- Toxicology Drug Testing
- PDS. Pre-employment drug screening. Intro to Drug Screening. Accessed February 14, 2012 - www.employmentdrugtesting.com/screening.html
- Surgeon General's Report; 2004. ONDCP; Harwood 2000. Accessed 4/9/2013. National Institute on Drug Abuse
- Substance Abuse and Mental Health Services Administration. Division of Workplace Programs. Prescription Drug Abuse in the Workplace.
- Doering, PL, Boothbay LA. Drug Testing in the Workplace: What the pharmacist should know. Drug Topics (Modern Medicine) 2003;147:63. Accessed online September 7, 2012. http://www.modernmedicine.com/modernmedicine/article/articleDetail.jsp?id=111093
- Lab Tests Online. Drugs of Abuse Testing. Accessed 4/9/2013. http://labtestsonline.org/understanding/analytes/drug-abuse/tab/sample
- LabCorp. Drugs of Abuse Reference Guide. 2007. Accessed 4/9/2013. https://www.labcorpsolutions.com/images/Drugs_of_Abuse_Reference_Guide_Flyer_3166.pdf
Last updated: 2013-04-09 by L. Anderson, PharmD