A DOT drug test detects substance use from roughly the past one to 30 days, depending on the drug and how frequently you’ve used it. The standard test is a urine screen, and each substance has its own detection window. A positive result then stays on your FMCSA Clearinghouse record for five years, which is a separate but related concern for many drivers searching this question.
What a DOT Drug Test Screens For
DOT testing follows federal rules under 49 CFR Part 40 and checks for five classes of drugs: marijuana, cocaine, opiates (opium and codeine derivatives), amphetamines and methamphetamines, and PCP. Alcohol testing is separate and flags a blood alcohol concentration of 0.02 or greater, but alcohol leaves the body within hours, so the “how far back” question really applies to the five drug categories.
Detection Windows by Substance
The detection window is the period after your last use during which the drug or its byproducts can still show up in urine. These windows vary quite a bit from one substance to another.
Marijuana (THC) has the widest range. If you smoked once, cannabinoids are typically detectable for about three to four days at the standard 50 ng/mL cutoff used in DOT screening. At a lower 20 ng/mL cutoff (used in some confirmatory steps), a single use could show up for roughly seven days. For daily or heavy users, the window extends significantly, but research from the Drug Court Review found that even chronic smokers would not remain positive beyond 21 days after stopping, even at the lower cutoff. THC is stored in body fat, which is why heavier or more frequent users clear it more slowly.
Cocaine itself leaves the body quickly, often within a day. But the metabolite that labs actually test for, benzoylecgonine, stays detectable for up to four days.
Amphetamines and methamphetamines are generally detectable for two to five days after use.
Opiates vary depending on the specific drug. Short-acting opioids like hydromorphone are typically detectable for up to three days. Codeine and morphine follow a similar timeline. Some longer-acting opioids may linger slightly longer, but the general range is one to four days for most substances in this class.
PCP can be detected for roughly one to two weeks in occasional users. Chronic PCP use can push that window out further, though PCP use is relatively uncommon among the general population being tested.
Why It’s Always a Urine Test
DOT-regulated testing currently requires a urine specimen collected at a certified lab. There is no approved alternative for meeting your DOT testing obligation right now. The Department of Transportation published guidelines for oral fluid (saliva) testing in January 2025, but as of that publication, no labs have been certified to perform oral fluid tests under DOT rules. Until at least two certified labs are up and running, saliva testing cannot be used for DOT purposes.
Hair testing is another method you may have heard about. Some trucking companies use hair tests on their own, but hair results cannot be reported to the FMCSA Clearinghouse and do not satisfy DOT requirements. FMCSA denied a 2022 request from the Trucking Alliance to change this, noting that the Department of Health and Human Services has not finalized mandatory guidelines for hair testing. A hair test can detect drug use going back approximately 90 days, but until federal standards are established, it has no role in official DOT compliance.
Factors That Shift the Window
The ranges above are averages. Several factors can push your personal detection window shorter or longer. Body fat percentage matters most for THC, since cannabinoids accumulate in fat tissue and release slowly. A lean person who used marijuana once might clear it in two days, while someone with a higher body fat percentage might take the full four.
Hydration plays a role too. A well-hydrated person produces more dilute urine, which can lower the concentration of drug metabolites. However, DOT labs check for overly dilute specimens, and a dilute result may require you to retest. Metabolism, age, kidney function, and the potency or dose of the substance all contribute as well, but frequency of use is consistently the biggest factor across all drug classes.
How Long a Positive Result Follows You
The detection window tells you how far back a single test can look. But if that test comes back positive, the consequences extend much further. A violation recorded in the FMCSA Drug and Alcohol Clearinghouse remains available to employers for five years from the date of the violation, or until you complete the full return-to-duty process and follow-up testing plan, whichever takes longer.
The return-to-duty process involves evaluation by a substance abuse professional, completing any recommended treatment or education, passing a return-to-duty drug test, and then undergoing follow-up testing for a period determined by the evaluator (a minimum of six direct-observation tests over the first 12 months). Until that entire process is finished, the violation stays active on your record. Any employer running a Clearinghouse query before hiring or assigning you to safety-sensitive duties will see it.
Pre-employment queries are mandatory. So even if a positive test happened four years ago, a new employer will know about it unless you’ve completed every step of the return-to-duty requirements and the five-year clock has run out.
Quick Reference: Detection Windows
- Marijuana (single use): 3 to 4 days
- Marijuana (daily use): up to 21 days
- Cocaine: up to 4 days (metabolite)
- Amphetamines: 2 to 5 days
- Opiates: 1 to 4 days
- PCP: 7 to 14 days (occasional use)