What Is a Medical Review Officer (MRO)?

What an MRO Does

A Medical Review Officer (MRO) is a licensed physician who receives and reviews drug test results from laboratories before those results are communicated to employers. The MRO serves as an independent, objective safeguard that ensures results are interpreted accurately and fairly.

Without MRO review, an employee taking a legitimately prescribed medication could receive a verified positive on a drug test — and potentially lose their job — for something entirely lawful.

MRO Requirements Under DOT

For DOT-regulated drug testing, MRO review is mandatory for every specimen result — positive, negative, canceled, and substituted. The MRO must:

• Hold an active medical license in the U.S.
• Have completed DOT MRO training and passed a qualifying examination
• Maintain continuing education in substance abuse disorders and drug testing

What Happens When a Lab Reports a Positive

When a laboratory reports a non-negative (positive, adulterated, substituted, or invalid) result, the MRO:

1. Contacts the donor directly — not the employer — to determine if there is a legitimate medical explanation
2. Gives the donor an opportunity to present documentation of a valid prescription or medical condition
3. Reviews any submitted documentation
4. Makes a determination: verified positive (no legitimate explanation) or verified negative (legitimate explanation confirmed)

The employer is notified only after the MRO has made this determination.

When Results Can Be Reported as Negative

The MRO can report a result as negative when the donor provides documentation of:

• A valid prescription for the substance detected
• A medical condition that explains an unusual specimen characteristic
• Other legitimate clinical explanation for the laboratory findings

For DOT testing, there is one significant exception: marijuana has no DOT-acceptable medical explanation, even in states where it is legal. A positive THC result cannot be verified negative, even with a valid medical marijuana card.

MRO for Non-DOT Testing

MRO review is not federally required for non-DOT drug testing, but many employers choose to use MRO services because:

• It reduces the risk of adverse action against an employee taking lawful medication
• It provides a legally defensible review process
• It protects the employer from ADA-related claims

What Employers Receive

After MRO review, employers receive a final verified result: negative, positive, canceled, refusal to test (adulterated or substituted), or negative with a safety concern. The MRO does not share specific prescription information with the employer — only the final determination.

At Do It Right Screening, MRO services are integrated into our drug testing programs. Contact us to learn how we handle the full testing process from collection through final result.