A standard drug test screens for five categories of substances: marijuana (THC), cocaine, amphetamines, opioids, and PCP. This five-panel urine test is the baseline for most workplace and government-mandated screening. Expanded panels (7, 10, 12, or more) add categories like benzodiazepines, barbiturates, and alcohol. But beyond just checking for drugs, labs also test whether your sample is legitimate.
The Standard 5-Panel Test
The five-panel drug test is the format used across all Department of Transportation regulated industries, including trucking, aviation, rail, public transit, pipelines, and maritime. It covers:
- THC (marijuana and cannabis products)
- Cocaine (including crack)
- Amphetamines (including methamphetamine and MDMA/ecstasy)
- Opioids (heroin, codeine, morphine, oxycodone, hydrocodone, and others)
- PCP (phencyclidine)
Many private employers use this same panel. Others expand it to 10 or 12 substances, adding benzodiazepines (like Xanax or Klonopin), barbiturates, methadone, propoxyphene, and sometimes synthetic opioids like fentanyl. The specific panel depends on who ordered the test and why.
What the Lab Actually Detects
Drug tests rarely look for the drug itself. Your body breaks substances down into byproducts called metabolites, and those are what show up in your urine. This matters because metabolites can linger long after the drug’s effects have worn off.
For marijuana, labs detect a metabolite called THC-COOH, not THC directly. Most lab testing does not distinguish between delta-9 and delta-8 THC, so both can trigger a positive result. THC metabolites have the widest detection window of any commonly tested substance: anywhere from 1 to 45 days, depending on how frequently and how much you use.
Cocaine itself disappears from urine in less than a day because it has a very short half-life (under two hours). Instead, labs look for a metabolite called benzoylecgonine, which stays detectable for one to two days. Heroin is similar. It breaks down so quickly that the parent drug is essentially never found. Labs screen for a heroin-specific metabolite (6-acetylmorphine) and for morphine, which heroin converts into.
Prescription opioids each produce their own characteristic metabolites. Hydrocodone, oxycodone, and oxymorphone are generally detectable for one to three days. Methadone has a much longer window, sometimes up to 14 days, because of its unusually long half-life.
Benzodiazepines, when included on an expanded panel, vary widely. A short-acting one like midazolam clears in one to two days. A long-acting one like diazepam (Valium) can be detected for up to 10 days because its metabolites persist much longer in the body.
Alcohol Testing
Standard five-panel tests do not include alcohol, but many employers add it. A breath test or standard blood alcohol check only catches very recent drinking. For a longer look-back window, labs test for ethyl glucuronide (EtG), a metabolite your liver produces when it processes alcohol. At a cutoff of 100 ng/mL, EtG testing can detect heavy drinking for up to five days and any drinking within the previous two days. That 100 ng/mL threshold picks up roughly 79% of heavy drinking episodes over a five-day window.
How Initial Screening Works
Drug testing happens in two stages. The first is a rapid immunoassay, a chemical test that flags whether a sample is above a set threshold for each substance category. This initial screen is fast and inexpensive, but it casts a wide net. It can react to substances that are chemically similar to the target drug, which is why false positives happen.
If the initial screen comes back positive, the sample goes through confirmatory testing. The gold standard method uses a technique that separates the sample into its individual chemical components and then identifies each one by its molecular structure. This confirmation step is highly specific and essentially eliminates false positives from the initial screen. A result is only reported as positive after it passes both stages.
Common Causes of False Positives
Several over-the-counter and prescription medications can trigger a positive on the initial immunoassay screen, even though you haven’t used any illicit substance. This is one reason the two-stage process exists.
For amphetamines, known triggers include pseudoephedrine (the decongestant in some cold medications), bupropion (an antidepressant and smoking-cessation aid), phentermine (a weight-loss medication), methylphenidate (used for ADHD), ephedrine, and ranitidine (a heartburn medication). Trazodone, a commonly prescribed sleep aid, can also cause a false positive for amphetamines.
For opioids, the most notable culprits are dextromethorphan (the cough suppressant in many OTC cold medicines), diphenhydramine (the active ingredient in Benadryl), and poppy seeds. The poppy seed issue is real, not a myth. Poppy seeds contain trace amounts of morphine and codeine, and eating enough of them can push a screening result above the cutoff threshold. Confirmatory testing will usually sort this out, but if you know a test is coming, it’s worth avoiding poppy seed bagels and pastries for a few days.
How Labs Check Your Sample Is Real
Labs don’t just test for drugs. They also run validity checks to catch diluted, substituted, or tampered samples. Every urine specimen is evaluated against several benchmarks within four minutes of collection.
Temperature is checked first. A valid sample falls between 90°F and 100°F. Outside that range, the collector flags it as suspicious. Beyond temperature, labs measure three key markers. Creatinine, a natural waste product in urine, should fall between 20 and 400 mg/dL. A creatinine level below 2 mg/dL suggests the sample may not be human urine at all, and it gets classified as “substituted.” A level between 2 and 20 mg/dL with a low specific gravity indicates dilution, which can happen from drinking excessive water before the test. The pH of normal urine ranges from 4.5 to 8.0. A reading below 3 or above 11 indicates the sample has been chemically adulterated.
A diluted result doesn’t automatically count as a failure, but many employers will require you to retest, sometimes under direct observation.
When Drug Testing Is Required
Federal drug testing is mandatory for safety-sensitive positions regulated by the Department of Transportation. This includes commercial truck drivers, airline pilots and mechanics, railroad workers, public transit operators, pipeline workers, and maritime crew. These workers face testing at six points: pre-employment, random selection, reasonable suspicion, post-accident, return-to-duty after a violation, and follow-up testing.
Outside of federal requirements, private employers set their own policies. Some test only at hiring, others randomly throughout employment. The substances tested and the cutoff levels can vary. If you’re unsure what panel applies to you, the paperwork from the testing lab or your employer’s drug-free workplace policy will specify exactly which substances are included.