How Far Back Does a DOT Drug Test Go?

Short answer: A standard DOT urine drug test detects most substances within roughly the last 1 to 4 days, but heavy marijuana use can be detected for 30 days or more.

Typical urine detection windows

• Marijuana (THC): 3 days for occasional use, up to 30+ days for heavy/daily use
• Cocaine: 2 to 4 days
• Opiates: 1 to 3 days (some semi-synthetics slightly longer)
• Amphetamines/methamphetamine: 1 to 3 days
• PCP: 1 to 8 days (longer with chronic use)

Why marijuana lasts longest

THC is fat-soluble and stored in body fat, then released over time. Frequency of use, body composition, metabolism, and hydration all affect how long it stays detectable.

Hair, saliva, and blood tests

The DOT-mandated test is urine. Hair tests (used by some carriers as a non-DOT add-on) can detect use going back roughly 90 days. Saliva and blood tests have much shorter windows than urine.

Cutoffs matter

Detection isn't pass/fail at any trace amount. HHS sets specific cutoff concentrations. A small amount below the cutoff is reported as negative.

Don't try to game it

Dilution, substitution, and adulteration are all detected by the lab and treated as a refusal — which is the same as a positive on your FMCSA Clearinghouse record.