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The Medical Review Officer (MRO) Process

A Medical Review Officer (MRO) is a licensed physician trained in drug testing interpretation. Under 49 CFR Part 40, every positive federal/DOT drug test must be reviewed by an MRO before being verified and reported to the employer. The MRO interview is your opportunity to provide a medical explanation. Knowing what to expect and how to prepare is essential.

Stethoscope, closed prescription pad, and pen on a physician

What the MRO Does

Per 49 CFR Part 40, Subpart G, the MRO is responsible for:

  1. Reviewing the lab result and chain of custody documentation
  2. Contacting the donor (you) within 24 hours of receiving a positive result
  3. Conducting a verification interview to discuss possible medical explanations
  4. Verifying the result as positive, negative, or cancelled based on the interview
  5. Reporting the verified result to the employer

The MRO is a neutral third party. They are not your advocate, but they are also not the employer's advocate. Their job is to make a medically informed determination about whether the positive result has a legitimate explanation.

The MRO Interview

The MRO will typically call you on the phone. Expect questions like:

  • "Is this [your name]?"
  • "I'm calling about your recent drug test. Are you in a private place where we can talk?"
  • "Your test came back positive for marijuana. Can you tell me about any medications or substances you've used recently that might explain this?"
  • "Are you currently taking any prescription medications?"
  • "Have you used any CBD products?"
  • "Do you have a state medical marijuana card?"

You have 5 business days from this initial contact to provide medical documentation supporting any explanation you give.

What Counts as a Legitimate Medical Explanation

The MRO can verify a result as negative if you provide:

  • A current prescription for a Schedule II–V medication that explains the positive (e.g., dronabinol/Marinol for cannabis)
  • Documentation that your testing was at fault (e.g., chain of custody errors)
  • A successful split specimen test that does not reconfirm the original

What does NOT count under federal MRO rules:

  • State medical cannabis card — explicitly excluded by 49 CFR § 40.151(e)
  • "I only used CBD" — CBD products are not prescription drugs and cannot serve as a medical explanation
  • Secondhand exposure — not a recognized medical explanation
  • Recreational legal use in a state where cannabis is legal
  • "It's been a while since I used"

The Dronabinol/Marinol Exception

Dronabinol (brand name Marinol) is a Schedule III prescription drug that contains synthetic THC. It is FDA-approved for chemotherapy-induced nausea and HIV-related anorexia. Because dronabinol is structurally identical to plant THC, it produces the same THC-COOH metabolite that drug tests detect.

If you have a current dronabinol prescription, the MRO will accept it as a legitimate medical explanation and verify the test as negative. You will need to provide:

  • A copy of the prescription
  • Pharmacy records showing the prescription was filled
  • Possibly contact information for your prescribing physician

How to Prepare for the MRO Call

  • Have your medication list ready. Include all prescriptions, OTCs, supplements, and CBD products.
  • Know your prescription details. Drug name, dose, prescribing physician, dates of use.
  • Have your pharmacy on speed dial in case you need to verify a prescription.
  • Take notes during the call. Date, time, what was said, what was requested.
  • Ask for the MRO's name and contact information.
  • Confirm any deadlines. The 5-business-day deadline for documentation is critical.
  • Confirm your right to request a split specimen test. The MRO is required to inform you of this right.

What to Say (and Not Say)

The MRO call is not a casual conversation. The MRO is documenting what you say. Some general guidance:

  • Be honest about prescriptions. Lying about medications can result in additional penalties.
  • Do not volunteer information beyond what is asked. "Yes, I take pantoprazole" is sufficient; "Yes, I take pantoprazole because I have acid reflux from stress at this awful job" is too much.
  • If asked about cannabis use directly, think carefully before answering. Admitting recreational use in a federal testing context provides evidence that is essentially conclusive against you. This is where legal advice helps.
  • If you do not understand a question, ask for clarification.
  • If you need time to consult a lawyer or gather documentation, request it.

What Happens After the Interview

After the MRO interview, the MRO will verify the result as one of:

  • Negative — if a legitimate medical explanation is provided and verified, OR if the split specimen test does not reconfirm
  • Positive — if no legitimate medical explanation is provided
  • Cancelled — if there are chain-of-custody or specimen validity problems that invalidate the test

The verified result is reported to the employer. The employer then takes whatever action is dictated by federal regulations (for DOT positions) or company policy (for non-DOT positions).

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