How does a drug test work? Here's what you need to know (2024)

As substance use disorder continues to be a major public health issue, drug testing has become a standard practice for purposes ranging from pre-employment screening to court-ordered monitoring. Here’s a look at how drug tests work and what you can expect if you need to take one.

What exactly is a drug test?

A drug test checks for the presence of drugs and their metabolites in your system. Metabolites are the substances left behind after the body breaks down drugs. The most common sample types used for drug tests are urine, blood, hair and saliva.

After you provide a drug test sample, it is sent to a lab for analysis. Initial drug screenings are performed using a method called immunoassay, which is a test that uses antibodies to detect the presence of drugs and their metabolites. While this screening doesn’t measure how much of a drug was used, it can indicate the presence or absence of drugs in the system. If screening indicates a presumptive positive for that drug, a second confirmation test is performed to confirm the positive results and provide the most accurate result.

What sample types are used for drug testing?

Drugs and their metabolites get stored in the body in different ways. For example, marijuana metabolites get stored in fat cells and are slowly released over time into urine. Other drugs like cocaine can be detected in urine for only a few days after use. Hair testing can detect drug use over a longer time, since trace amounts in the bloodstream get deposited into growing hair strands.

Some of the most common sample types used for drug testing include:

  • Urine: The most frequently used sample type. A urine drug test can detect recent drug use. The test requires providing a urine sample into a collection cup
  • Blood: Not as common as urine tests but can detect very recent drug use. The test requires having blood drawn by a medical professional
  • Hair: Used to detect longer-term drug use. The test requires snipping a small hair sample near the scalp
  • Saliva: Checks for very recent drug use. The test requires swabbing of the inside of the mouth

What drugs are included in drug test panels?

Many drug tests use a six-panel or expanded 11-panel test to check for multiple commonly used drugs. Certain drugs can stay in your system longer than others, so if you’re checking for the presence of a specific drug, it’s important to know how long that drug is detectable in your system.

A six-panel drug test typically tests for the drugs listed below. The times listed in parentheses indicate how long the drug metabolites may be detectable in urine.

  • Amphetamines like speed and methamphetamine (up to 2 days)
  • Cannabinoids like marijuana or THC (2-7 days for single use, 1-2 months for chronic use)
  • Cocaine (up to 4 days)
  • Opiates like morphine, hydrocodone or codeine (2-7 days depending on the opiate)
  • Oxycodone (1-4 days)
  • Phencyclidine or PCP (14 days for single use, up to 30 days for chronic use)


An expanded 11-panel adds tests for:

  • Barbiturates (2 days to 3 weeks)
  • Benzodiazepines like alprazolam or diazepam (up to 6 weeks)
  • Fentanyl (1-3 days)
  • MDMA or ecstasy (up to 2 days)
  • Methadone (about 3 days)

Preparing for and taking a drug test

There is no standard preparation for a drug test other than having a form of identification with you and being ready to provide a sample. However, it is recommended that you inform your testing professional of any over-the-counter medications or supplements you may be taking, as they may affect your test results. Avoiding foods with poppy seeds is also recommended, as they can be detected as a false positive for opiates in a drug test.

Results are usually available within 1-5 days. A positive result means the drug or metabolite was detected in your system. A negative result means drugs weren’t detected but does not mean there are no drugs present in your system. Following up with a healthcare professional is the best way to confirm your results.

Test your drug exposure with Labcorp OnDemand

Labcorp OnDemand offers multiple options for someone seeking drug testing for personal use or peace of mind. Our Standard Drug Test checks for six common drugs of abuse, and our Complete Drug Test is an expanded 11-panel test. Both require urine samples that must be collected in person at a Labcorp patient service center.

Convenient and reliable drug testing services can give you the insights you need into your drug exposure.

How does a drug test work? Here's what you need to know (2024)

FAQs

How does a drug test work? Here's what you need to know? ›

A drug test screens for certain drugs and/or their metabolites in a biological sample (such as urine or blood). The metabolic processes happen at different speeds for different drugs. Because of this, each drug and its metabolites have a different timeframe in which a drug test can detect them.

What exactly shows up on a drug test? ›

Test Quick Guide

Urine drug testing detects evidence of recent drug use or misuse in a sample of urine. Testing can detect illegal or prohibited drug use, prescription medications, over-the-counter medicines, and legal substances such as alcohol and tobacco.

What is checked during a drug test? ›

Tests are commonly used for five categories of drugs: Amphetamines; Cocaine; Marijuana; Opiates; and Phencyclidine (PCP). Additional categories may include barbiturates, Benzodiazepines, ethanol (alcohol), hydrocodone, MDMA, methadone, methaqualone, or propoxyphene.

How long does it take for a drug to be eliminated from the body? ›

Most drugs of abuse stay in the body for at least a few days after the last use and are traceable with urine tests. Opioids like heroin and oxycodone are detectable for between 1 and 3 days after last use. Stimulants including cocaine, meth, and ADHD medications are detectable for about 2 or 3 days.

How far back does a 10 panel urine test go? ›

How far back 10-panel drug tests go varies based on frequency of drug usage, individual rates of drug metabolism, and other factors. The detection window for most substances included in 10-panel drug testing is one to three days. However, some substances drugs may be detectable for longer based on chronic usage.

What will mess up a urine test? ›

Most household substances, such as bleach, salt, or vinegar, will radically alter the pH of your urine, which will make it obvious that you have tampered with the sample.

What determines if you fail a drug test? ›

Here are several situations that may result in a failed drug test. Drug or alcohol consumption can produce a positive test. Medications, such as antidepressants, NSAIDs, and decongestants may result in a false positive. Foods like hemp seeds, poppy seeds, and coca tea can trigger a false positive.

What is the most common false positive drug test? ›

Amphetamine (more on this below) and methamphetamine are the most commonly reported false positive.

What makes a urine drug test invalid? ›

Invalid result: Refers to the result reported by a laboratory for a urine specimen that contains an unidentified adulterant, contains an unidentified interfering substance, has an abnormal physical characteristic, or has an endogenous substance at an abnormal concentration that prevents the laboratory from completing ...

What all can a urine test detect? ›

The results of a urine test may indicate the presence of:
  • Diabetes or prediabetes.
  • Chronic kidney disease.
  • Kidney or bladder stones.
  • Kidney or bladder cancer.
  • Bacterial or yeast infections.
  • A urinary tract disorder.
  • Sexually transmitted infections (STIs)
  • Liver or bile duct damage.

Does drinking water help flush out medication? ›

Don't expect drinking a large amount of water at one time to be an effective way to remove drugs from your system. Staying hydrated requires frequency, not just volume. In addition to water, herbal teas and juice may help your body flush out toxins.

How can I speed up drug elimination? ›

The drug must be excreted rapidly from the body, so one strategy is to alter the urine pH to increase excretion. In aspirin poisoning for example, making the urine more alkaline with sodium bicarbonate increases ionisation of the salicylic acid (aspirin metabolite) therefore increasing its excretion from the body.

What can cause a false negative drug test? ›

False-negative results occur when a drug or metabolite is present at such low levels that it is not detected. Confirmatory testing is essential to distinguish a true negative from a false negative. Contaminants can also interfere with the immunoassay's ability to detect the presence of drugs.

What do employers look for in a drug test? ›

Common drugs tested for in a hair sample include methamphetamine, cocaine, marijuana, opioids, and PCP. A sample of 100 strands of hair cut close to the scalp is collected from the employee from an unnoticeable area of the head.

What should I avoid before a 10 panel drug test? ›

For 24 hours prior to collecting the specimen, you should avoid strenuous exercise as well as the following substances and drugs:
  • Acetaminophen.
  • Alcohol.
  • Antihistamines.
  • Aspirin.
  • Caffeine.
  • Vitamin B.

What is the cutoff level for drug tests? ›

Testing Cutoff Levels
Clinical Panels (ng/ml)Forensic / Workplace Panels (ng/ml)
Marijuana metabolites50*Marijuana metabolites
Cocaine metabolites300*Cocaine metabolites
Amphetamines1000*Amphetamines
AmphetamineAmphetamine
12 more rows

What is the most common pre-employment drug test? ›

Urinalysis – A urine test is the most common form of pre-employment drug testing and is typically conducted once a conditional offer of employment has been sent.

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