Medical review officer (MRO): who reviews a driver's drug test before you see it
Overview
A medical review officer (MRO) is the doctor who sees a driver's drug test result before the employer does. When the lab flags a specimen, the MRO talks to the driver and decides whether a valid prescription or another lawful medical reason accounts for it. The employer then gets the final result, with no drug levels and no medical details unless the MRO reports a safety risk.
On this page
What an MRO is
An MRO is a physician, an MD or a DO, who sits between the drug testing lab and the employer. Section 40.123 describes the job as an “independent and impartial ‘gatekeeper’ and advocate” for the accuracy and integrity of the drug testing process. In a DOT program, every lab result goes to the MRO first, and the employer hears only what the MRO verifies. The drug testing guide shows where this step sits in the life of a screen.
The qualifications in 40.121 go beyond a medical license:
- License. An MD or DO license in any U.S., Canadian, or Mexican jurisdiction covers employees everywhere, so the MRO need not be licensed in your state.
- Training and exam. Qualification training on collections, chain of custody, interpreting results, and the DOT rules, then a passing score on an exam given by a national MRO certification board.
- Requalification. New training and a new exam every five years.
The MRO may not take any financial benefit from the employer’s choice of lab (40.125). Reviewing a result does not create a doctor-patient relationship with the driver.
The verification interview
The interview is the driver’s main chance to explain a lab-confirmed result before it becomes a verified positive. How the MRO tracks the driver down is in the drug testing guide. On the call itself, the MRO names the drugs found, explains how the decision will be made, and warns the driver that medical information bearing on safety may be passed on without consent (40.135).
The burden is on the driver. If there is reason to think records exist, the MRO can hold the decision for up to five days while the driver gets them (40.137). A prescription that is “legally valid” and “consistent with the Controlled Substances Act” counts as an explanation, and the MRO may not second-guess the prescriber’s choice. The MRO may call the prescriber or the pharmacy to confirm the prescription is real (40.141).
Some explanations never work. Section 40.151 bars the MRO from accepting:
- A negative result from a test the driver arranged with their own doctor.
- A story of unknowing exposure, such as a spiked drink or someone else’s smoke.
- Hemp or other non-prescription marijuana products, or coca tea.
- A state medical marijuana card, a doctor’s recommendation, or dispensary receipts. State-licensed medical marijuana moved to Schedule III on April 28, 2026, but DOT’s drug and alcohol office answered in May 2026 that it still is not a legitimate medical explanation, because a state product is not FDA-approved and cannot be prescribed. The marijuana laws guide covers the rest of that change.
- Any explanation at all for PCP, 6-acetylmorphine (6-AM), MDMA, or MDA.
The MRO also stays out of disputes about the collection site and whether the employer had grounds to order the test.
What the employer receives
You receive the result, not the medical story. Verified positives, refusals for an adulterated or substituted specimen, and results that need an immediate observed recollection reach the employer’s designated representative the day of verification or the next business day, with a phone call preferred (40.167). The written report must arrive within two days of verification.
The report names the result and, for a positive, the drugs. It never includes drug levels: 40.163 bars MROs from giving quantitative values to employers. After a verified positive, the MRO also tells the driver of the right to have the split specimen tested, a request the driver can make within 72 hours of being told (40.153). For CDL drivers, the MRO reports verified positives to the FMCSA Clearinghouse within two business days.
A dilute result comes with instructions. When a negative-dilute specimen has creatinine between 2 and 5 mg/dL, the MRO tells you to send the driver for an immediate directly observed collection (40.155 and 40.67).
When the MRO reports a safety concern
A negative result can still come with a warning. Under 40.327, the MRO must tell the employer without the driver’s consent when information from the interview is likely to make the driver medically unqualified under a DOT rule, or shows that continued driving is likely to be a significant safety risk. The report comes as a separate letter or secure email, never on the custody form, and states the specific concern.
Before passing on a prescription concern, the MRO gives the driver time. For a medication taken under a valid prescription, the MRO allows 5 business days after reporting the verified negative for the prescribing doctor to call and discuss switching to a medicine that does not raise the concern (40.135). As an example, a driver whose oxycodone screen is explained by a prescription gets a verified negative, and the MRO may still send a safety letter if, in the MRO’s medical judgment, the medication makes driving a significant safety risk.
An MRO for non-DOT testing
Most NEMT drivers are tested under broker and company rules rather than DOT, and Part 40, MRO rules included, covers only tests that DOT rules require (40.1). Two laws make an MRO worth paying for anyway.
- The ADA. Drug screens for illegal use fall outside the ADA’s limits on medical exams (42 U.S.C. 12114(d)), but asking employees about their prescriptions is a disability-related inquiry. The EEOC’s guidance says asking all employees what prescription drugs they take is generally not job-related, with a narrow exception for safety jobs where impaired work would be a direct threat. Sending a non-negative result to an MRO keeps the medication conversation between the driver and a physician, not a dispatcher.
- Florida’s drug-free workplace law. Employers that want the workers’ compensation premium discount under 627.0915, and the right to deny comp benefits under the drug-free workplace rules, must test the way 440.102 sets out. It bars firing, disciplining, or refusing to hire solely on a positive result that has not been verified by a confirmation test and an MRO, and the employer’s written policy must let the driver contest or explain a confirmed positive to the MRO within 5 working days after written notice.
An instant cup is only a screen. The drug testing guide’s section on lab tests versus instant cups covers state limits on them. The fill-in drug and alcohol policy sends every non-negative result to an MRO.
Frequently asked questions
- Can a verified positive be changed later?
- Only by the MRO, and only in the cases 49 CFR 40.149 lists: reopening a result verified without an interview, a lab error discovered afterward, an administrative mistake by the MRO, or new information within 60 days of the decision, such as a valid prescription the driver could not produce in time, that shows a legitimate medical explanation. When that kind of information arrives after 60 days, the MRO must consult DOT's drug and alcohol office first. An arbitrator cannot overrule the MRO's medical judgment, and any change goes to the employer in writing right away.
- When can the MRO decide without talking to the driver?
- Once the employer's designated representative has reached the driver and told them to call the MRO, the MRO may verify the result without an interview after 72 hours. If nobody can reach the driver despite documented efforts, the MRO may verify after ten days from receiving the lab result. A driver who was seriously ill or injured has 60 days after verification to ask the MRO to reopen it.
- Who pays for testing the split specimen?
- The employer has to make sure the test happens when the driver asks within 72 hours of the MRO's notice, and the driver cannot be required to pay first. The employer may then seek reimbursement from the driver under 49 CFR 40.173. Settle how that works in your written policy.
- Does the MRO look at negative results too?
- Yes. Before releasing a negative, the MRO's office checks the custody and control form for errors that could cancel the test. Staff under the MRO's supervision may handle negatives, but the MRO must personally review at least 5 percent of those forms each quarter, up to 500 negatives.
