What Explanations Can an MRO Not Accept for a DOT Drug Test Result?

49 CFR 40.151 lists what an MRO is prohibited from doing during verification. Under 40.151(a), the MRO must not consider evidence from drug tests that were not collected or tested under Part 40. The rule's example is an employee who provided a urine specimen through a personal physician and received a negative result, which the MRO is required to ignore.

Under 40.151(b) and (c), it is not the MRO's function to decide factual disputes about events at the collection site that are not reflected on the CCF, or to decide whether the employer should have directed the test. Under 40.151(d), the MRO must not declare a test negative based on an explanation that would not be a legitimate medical explanation even if true. The rule's examples are passive or unknowing ingestion stories, such as amphetamines slipped into a drink, an unknowingly eaten marijuana brownie or travel in a closed car with people smoking crack.

Under 40.151(f), the MRO must not accept consumption or other use of "a hemp or other non-prescription marijuana-related product" as a basis for verifying a marijuana test negative, or consumption of coca teas as a basis for verifying a cocaine result negative. The rule states that consuming or using such a product "is not a legitimate medical explanation." Section 40.151(e) bars verifying a test negative based on a physician's recommendation to use a Schedule I drug, and 40.151(g) bars accepting a legitimate medical explanation for PCP, 6-AM, MDMA or MDA. A Drug Enforcement Administration final rule published April 28, 2026 (91 FR 22714) placed FDA-approved drug products containing marijuana, and marijuana covered by a state medical marijuana license, in Schedule III. Under DOT guidance last updated May 15, 2026, a state medical marijuana card does not allow an MRO to verify a laboratory-confirmed marijuana positive DOT drug test as negative, as covered in the FAQ linked below.

For adulterated and substituted specimens, 40.151(h) and (i) bar the MRO from accepting an assertion that certain adulterants named in the rule entered a specimen through physiological means, or that a person can produce urine with creatinine below the laboratory's limit of detection.

State marijuana programs are covered in Does a State Medical Marijuana Card Excuse a Positive DOT Drug Test?, and MRO review of adulterated or substituted results in How Does an MRO Review an Adulterated or Substituted DOT Drug Test?.

MRO listings in the MyDrugTesting.com directory that include a phone number have a Show Phone button.