Most drug tests screen for five categories of substances: marijuana, cocaine, amphetamines, opioids, and PCP. This standard five-panel test is the baseline for federal workplace testing, and it’s what you’ll encounter in most pre-employment screenings. Expanded panels add more substances to the list, and different specimen types (urine, hair, saliva) change how far back the test can look.
The Standard Five-Panel Test
Federal guidelines from the Substance Abuse and Mental Health Services Administration (SAMHSA) define the five drug categories that all regulated workplace tests must cover:
- Marijuana (THC): Tests detect the inactive metabolite your body produces after processing THC, not THC itself.
- Cocaine: The test picks up a breakdown product called benzoylecgonine that stays in your system after cocaine is metabolized.
- Amphetamines: This includes methamphetamine, MDMA (ecstasy), and MDA.
- Opioids: The category covers heroin, codeine, morphine, hydrocodone, hydromorphone, oxycodone, and oxymorphone.
- Phencyclidine (PCP): Also known as angel dust.
This five-panel format is what the Department of Transportation requires for truckers, pilots, and other safety-sensitive workers. Many private employers use it as well, though they aren’t legally required to follow the federal standard.
What Expanded Panels Add
When an employer or court orders a 10-panel or 12-panel test, the additional substances typically include benzodiazepines (like alprazolam and diazepam), barbiturates (like phenobarbital), methadone, and sometimes synthetic opioids like fentanyl. Some panels also screen for anabolic steroids or club drugs.
Alcohol testing is sometimes included as a separate add-on. Rather than measuring alcohol directly, many urine tests look for a metabolite called ethyl glucuronide (EtG), which your liver produces in small amounts after you drink. EtG can detect alcohol use for up to five days depending on how much you drank and which cutoff the lab uses. At the most sensitive cutoff of 100 ng/mL, the test picks up over 76% of light drinking episodes two days later. At the less sensitive 500 ng/mL cutoff, it mostly catches heavy drinking from the previous day only.
How the Testing Process Works
Drug testing happens in two stages. The initial screen uses a technique called immunoassay, which is fast and inexpensive but not perfectly precise. It works by using antibodies that react to drug metabolites in your sample. If this first screen comes back below a set cutoff concentration, the result is reported as negative and nothing else happens.
If the initial screen hits or exceeds the cutoff, the lab runs a confirmation test using a much more accurate method, typically gas chromatography-mass spectrometry (GC-MS). This second test can identify the exact substance and its concentration, effectively ruling out false positives from the initial screen. A result is only reported as confirmed positive if it meets or exceeds the confirmation cutoff too.
For marijuana, the initial screening cutoff is 50 ng/mL. The confirmation cutoff drops to 15 ng/mL. Cocaine’s initial cutoff is 150 ng/mL, with confirmation at 100 ng/mL. Amphetamines screen at 500 ng/mL and confirm at 250 ng/mL. These thresholds are set by federal regulation, so trace amounts that fall below the cutoff will not trigger a positive result.
Detection Windows by Specimen Type
How far back a test can see depends entirely on what type of sample is collected.
Urine is the most common specimen. Cocaine and most opioids are detectable for one to three days after use. Amphetamines and methamphetamine show up for two to four days. Marijuana varies the most: casual use clears in one to three days, daily use takes five to ten days, and chronic heavy use can remain detectable for up to 30 days because THC metabolites accumulate in body fat and release slowly.
Blood and saliva have much shorter windows, generally 12 to 24 hours for most substances. Marijuana in saliva may only be detectable for 4 to 10 hours after smoking. These methods are better for catching very recent use, which is why saliva tests are sometimes used for post-accident or reasonable-suspicion testing.
Hair testing looks back the farthest. Hair grows at roughly half an inch per month, so a standard 1.5-inch sample cut from the scalp captures approximately 90 days of drug use history. Hair testing is highly reliable for cocaine, opioids, methamphetamine, PCP, and MDMA. It’s less useful for detecting a single, isolated instance of use because it works best at identifying repeated exposure over time.
Specimen Validity Checks
Labs don’t just test for drugs. They also check whether the sample itself is legitimate. Every urine specimen is tested for creatinine concentration, pH, and specific gravity. These measurements reveal whether a sample has been diluted with water, substituted with a synthetic liquid, or chemically tampered with using an adulterant like bleach or an oxidizing agent.
If your creatinine level is below 20 mg/dL, the lab runs additional specific gravity testing to determine whether the sample is too dilute to be reliable. Abnormal pH or unusual reactions during the drug test itself also trigger further scrutiny. A specimen flagged as substituted or adulterated is treated as a refusal to test in federal programs.
What Can Cause a False Positive
The initial immunoassay screen can sometimes react to substances that are structurally similar to the target drug. Poppy seeds are the classic example for opioids, and they genuinely can trigger a positive at sensitive cutoff levels. Certain antibiotics (quinolones), the blood pressure medication verapamil, the antihistamine diphenhydramine (Benadryl), and the antipsychotic quetiapine have all been documented to cause false positives on opiate or methadone screening tests.
This is exactly why the two-stage testing process exists. The confirmation test using GC-MS is specific enough to distinguish between a drug and a medication that merely looks similar to the initial screen’s antibodies. If you’re taking a prescription medication that could cross-react, disclosing it to the Medical Review Officer (the physician who reviews results) allows them to verify your prescription and rule out a true positive.
CBD Products and THC Risk
Drug tests do not screen for CBD itself. However, many CBD products contain trace amounts of THC, and that THC can accumulate with regular use. Research analyzing commercially available CBD products found that 24% of items labeled “THC Free” actually contained detectable levels of THC, with concentrations ranging from 0.015 to 0.656 mg/mL. Some studies suggest that consuming less than 0.4 mg of THC per day could produce a positive urine test, a threshold easily reached by some contaminated products. There have been documented cases of people failing workplace drug tests after using CBD products they believed contained no THC at all.
The federal workplace cutoff for the marijuana metabolite is 50 ng/mL on the initial screen and 15 ng/mL on confirmation. If you use CBD products regularly and face drug testing, the only way to eliminate risk entirely is to avoid products that aren’t verified by independent third-party lab testing for THC content.