How to Detect Tampered Drug Tests

As drug test adulteration becomes more sophisticated, so do detection methods

Raeesa Gupte, PhD

Raeesa Gupte, PhD, is a freelance medical and science writer and editor specializing in evidence-based medicine, neurological disorders, and translational diagnostics. She holds a PhD in pharmacology from The University of Iowa.

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Published:Nov 30, 2019
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The Drug-Free Workplace Act, passed in the US in 1988, prohibits federal employees, contractors, and grantees as well as those in federally regulated industries or safety- and security-related industries from possessing or using controlled substances. Although not mandated, several private employers have also adopted a drug-free workplace policy. Outside of the workplace, drug testing is regularly employed in health care, sports, and forensics.

People cheat on drug tests for a variety of reasons—to retain their jobs, keep their medals, avoid going to prison, and maintain their spotless reputations. In fact, cheating on drug tests has essentially become an industry in its own right.

Types of drug tests

Drug tests commonly follow a two-step process. First, immunoassays provide a qualitative “yes” or “no” answer to whether the drugs being tested for are present in the biological sample. Immunoassays use antibodies to detect the presence of specific drugs and/or their metabolites. If drug concentrations in the sample are below the designated threshold value, it indicates a negative result. If the initial screen yields a positive result, samples are processed for further confirmation and quantification. In the second confirmatory step, gas chromatography-mass spectrometry (GC-MS), liquid chromatography-mass spectrometry (LCMS), or LC tandem mass spectrometry (LC-MS/ MS) is performed on the samples. These techniques separate the compounds in the samples, which are then identified based on their unique molecular fingerprints and quantified.

Drug testing can be performed on several types of biological samples, each with their own pros and cons.

How long do drugs stay in the body?

Workplace drug testing is based on the Substance Abuse and Mental Health Services Administration’s five-panel immunoassay, commonly referred to as SAMHSA-5. This panel traditionally tests five categories of drugs: amphetamines, marijuana, cocaine, opiates, and phencyclidine (PCP).

Most commercially available drug screens also test for alcohol, barbiturates, benzodiazepines, MDMA (ecstasy), and synthetic opioids (oxycodone, hydrocodone, buprenorphine, and methadone) in addition to the SAMHSA- 5 panel. Table 1 shows the average duration over which these drugs can be detected in various biological matrices.2

SubstanceUrineHairSaliva/Oral FluidBlood


Alcohol10-12 hoursUp to 90 daysUp to 24 hoursUp to 6 hoursN/A
Amphetamines2-4 daysUp to 90 days1-48 hoursUp to 48 hours7-14 days
Methamphetamine2-5 daysUp to 90 days1-48 hoursUp to 48 hours7-14 days
BarbituratesUp to 7 DaysUp to 90 daysN/AUp to 48 hoursN/A
BenzodiazepinesUp to 7 DaysUp to 90 daysN/AVariesN/A
Marijuana1-30 DaysUp to 90 daysUp to 24 HoursUp to 36 Hours7-14 days
Cocaine1-3 DaysUp to 90 days1-36 HoursUp to 48 hours7-14 days
Codeine2-4 DaysUp to 90 days1-36 HoursN/A7-14 days
Morphine2-5 DaysUp to 90 days1-36 HoursUp to 20 Hours7-14 days
Heroin2-3 DaysUp to 90 days1-36 HoursUp to 20 Hours7-14 days
Oxycodone2-4 DaysN/AN/AN/AN/A
Hydromorphone2-4 DaysN/AN/AN/AN/A
Methadone3 DaysN/AN/AN/AN/A
Propoxyphene6-48 HoursN/AN/AN/AN/A
Phencyclidine (PCP)5-6 DaysUp to 90 daysN/AUp to 24 Hours7-14 days
MDMA (EcstacyUp to 48 HoursN/AUp to 24 HoursUp to 24 HoursN/A

Ways to beat a drug test

Owing to privacy concerns, urine collection is often performed unobserved. Therefore, urine samples are most amenable to manipulation in the following ways:3

1. Substitution

To avoid a positive result, test takers substitute a synthetic urine or drug-free urine from another person or from an animal.

2. Dilution

Dilution of urine samples takes many forms. Water or other liquids may be added to the collected sample to dilute it. Alternatively, test takers may drink lots of water or consume products marketed as “detox” drinks, which claim to rid the body of drugs, anywhere from a few hours to a few days prior to sample collection. The mechanisms of action of these products are often unknown but likely involve dilution of urine in order to lower the concentration of drug(s) below detection limits. 4 The side effects may vary from changing urine color to causing intestinal issues and nausea. Some so-called detoxifiers also claim to render a negative result on hair tests following varying periods of abstinence.

3. Adulteration

In vitro adulteration involves addition of substances to urine after sample collection that will interfere with the test results. A slew of adulterants, including household substances (vinegar, detergent, bleach, iodine, isopropyl alcohol, and eye drops), food items (lemon juice and soda), and commercially available chemicals (nitrite, glutaraldehyde, and pyridinium chlorochromate), are regularly used to cheat a drug test. These substances may interfere with the detection of some but not all drugs on the test panel. For instance, pyridinium chlorochromate (PCC) may reduce detection of morphine and marijuana5 but increase sensitivity to amphetamines without affecting the detection of PCP. Depending on the concentration used, glutaraldehyde may produce false-negative results for marijuana, amphetamine, methadone, benzodiazepine, and cocaine metabolites.6 The mechanism by which adulterants produce false-negative results may vary. Nitrites, peroxides, and chromates may hamper the detection of drugs and their metabolites by oxidizing them, for example, whereas glutaraldehyde may interfere with the enzymes used in certain assays.

How to detect a tampered drug test

1. Physicochemical characteristics

Changes in the appearance and odor are usually the first indications of sample manipulation. Dilution of urine by drinking excessive water may produce a clear, almost water-like appearance. In contrast, urine detoxifiers may produce unnaturally colored urine. However, some detoxifiers contain niacin that imparts a natural yellow color and is not flagged as an adulterant. Adulteration with vinegar, bleach, or alcohol can be detected by the distinctive odors they produce. Turbidity or excessive frothing indicates addition of detergents. Because human urine has several known physiochemical values— temperature between 32 degrees Celsius and 38 degrees Celsius (when freshly collected), specific gravity between 1.002 and 1.02, creatinine concentrations above 20 mg/ dL, and pH of 4.5-9—deviations from these ranges are indicative of dilution or substitution.

2. Spot testing for adulterants

Several colorimetric reactions can be used to detect the presence of specific adulterants such as nitrite, PCC, and glutaraldehyde. For instance, hydrogen peroxide turns urine adulterated with PCC brown, and potassium permanganate added to urine adulterated with nitrite turns from pink to colorless upon addition of hydrochloric acid.

3. Adulteration test strips

Several on-site adulteration detection strips and devices are commercially available. Certain urinalysis tests contain individual strips that can detect pH, creatinine, glutaraldehyde, nitrites, PCC, and other oxidants.

The changing landscape of drug test cheating

Positive results on workplace drug testing continue to rise in certain sectors such as transportation and construction. The widening chasm between legalization of marijuana in several states and federal drug-free workplace policies may further spur cheating on drug tests. As the sale of drug-free urine is being banned in some states, and several states have pending legislation that would ban the use and sale of synthetic urine, ways to obfuscate drug tests get ever more creative (e.g., powdered urine kits and home remedies such as washing hair three to four times a day with vinegar and salicylic acid). As such, detection methods ultimately end up playing catch-up with the deviousness of drug test cheats.


1. Boscolo-Berto, Rafael, et al. “Sensitivity and specificity of EtG in hair as a marker of chronic excessive drinking: pooled analysis of raw data and meta-analysis of diagnostic accuracy studies.” Therapeutic Drug Monitoring 36.5 (2014): 560-575.

2. Hadland, Scott E., and Sharon Levy. “Objective testing: urine and other drug tests.” Child and Adolescent Psychiatric Clinics 25.3 (2016): 549-565.

3. Jaffee, William B., et al. “Is this urine really negative? A systematic review of tampering methods in urine drug screening and testing.” Journal of Substance Abuse Treatment 33.1 (2007): 33-42.

4. Cone, Edward J., Robert Lange, and William D. Darwin. “In vivo adulteration: excess fluid ingestion causes false-negative marijuana and cocaine urine test results.” Journal of Analytical Toxicology 22.6 (1998): 460-473.

5. Wu, Alan HB, et al. “Adulteration of urine by ‘Urine Luck.’” Clinical Chemistry 45.7 (1999): 1051-1057.

6. George, S., and R. A. Braithwaite. “The effect of glutaraldehyde adulteration of urine specimens on Syva EMIT II drugs-ofabuse assays.” Journal of Analytical Toxicology 20.3 (1996): 195-196.