Workplace Drug Testing: DOT Rules, OSHA's Post-Accident Policy, and What Employers Get Wrong

Most employers think drug testing is straightforward: set a policy, send people to a collection site, and act on results. That works fine until you have a post-accident situation, an employee in a state with cannabis protections, or a DOT-covered driver who tests positive. At that point, the gaps in policy become expensive.

Workplace drug testing actually runs on two separate tracks, with different legal frameworks, different testing events, and different consequences for getting it wrong.

DOT-Mandated Testing: Federal Rules for Safety-Sensitive Work

The Department of Transportation’s drug and alcohol testing regulations (49 CFR Part 40) apply to specific categories of safety-sensitive employees in federally regulated transportation. If your workforce includes any of the following, you have a DOT testing obligation, not just an employer option.

FMCSA covers commercial motor vehicle drivers who hold a CDL and operate vehicles with a gross vehicle weight rating above 26,001 pounds or transport hazardous materials in quantities requiring a placard. The FAA covers airline pilots, flight attendants, flight instructors, and air traffic controllers. The FRA covers railroad operating employees in safety-sensitive functions. PHMSA covers pipeline workers in operations, maintenance, and emergency response. The FTA covers transit workers operating revenue vehicles, dispatching, and maintenance on revenue vehicles.

For all of these workers, DOT requires six types of testing. Pre-employment testing before any safety-sensitive duty begins. Random testing throughout employment, drawn from a random testing pool at rates set annually by each DOT agency. Post-accident testing when certain thresholds are met (for FMCSA drivers, that is a fatal accident, an injury requiring immediate medical treatment away from the scene, or a vehicle disabled and towed). Reasonable suspicion testing when a supervisor observes specific, contemporaneous, documented signs of impairment. Return-to-duty testing after a verified positive or a refusal to test. Follow-up testing after return-to-duty, with a minimum of six unannounced tests in the first 12 months.

DOT testing uses a 5-panel drug screen covering marijuana metabolites, cocaine, opiates, amphetamines, and phencyclidine (PCP). The specimen must be collected at a DOT-compliant collection site, tested at a SAMHSA-certified laboratory, and reviewed by a Medical Review Officer before results go to the employer.

For complete current requirements, the DOT’s Office of Drug and Alcohol Policy and Compliance maintains the regulation and guidance at transportation.gov/odapc.

The Medical Review Officer’s Role

Every DOT-regulated testing program requires a Medical Review Officer (MRO). The MRO is a licensed physician with specific training in federal drug testing regulations. Before a positive result is reported to the employer, the MRO contacts the employee directly to ask whether there is a legitimate medical explanation for the result.

This step protects employees and protects employers. If an employee is taking prescribed opioids following surgery, the MRO can verify the prescription, confirm it was legitimately prescribed, and report the result as negative to the employer. If there is no valid explanation, the MRO reports the result as positive and the DOT return-to-duty process begins.

Non-DOT employers are not required to use an MRO, but some do. It adds a layer of procedural defensibility and reduces the risk of adverse action against an employee whose positive result had a legitimate explanation.

The Substance Abuse Professional and Return-to-Duty

A DOT-covered employee who receives a verified positive test result, or who refuses to test, is immediately removed from safety-sensitive duty. They cannot return until completing the full Substance Abuse Professional process.

The SAP is a licensed clinical professional with specific training under 49 CFR Part 40. The SAP evaluates the employee, recommends a specific course of education or treatment, and then conducts a follow-up evaluation to confirm that the recommendations were followed. Only after the follow-up evaluation does the SAP authorize the employee to take a return-to-duty test. A negative return-to-duty test result allows the employee to resume safety-sensitive work, but follow-up testing continues: at least six unannounced tests within the first 12 months, with the SAP able to extend that requirement up to five years.

The employer does not control the timeline. It is not a waiting period or a disciplinary leave. It is a structured clinical process that the employee must complete at their own pace, and the employer is required to maintain records documenting it.

OSHA’s Post-Accident Testing Rule: What Most Employers Get Wrong

For non-DOT employers, post-accident drug testing is discretionary, and this is where many policies create legal exposure they don’t know they have.

OSHA’s 2016 anti-retaliation final rule, codified in 29 CFR 1904.35(b)(1)(iv), includes guidance clarifying that blanket post-accident drug testing policies can deter injury reporting and violate the rule. OSHA’s position, explained in the October 2016 interpretation letter that is the direct source for this policy, is that requiring drug testing after every workplace injury or illness, regardless of the circumstances, may discourage workers from reporting injuries because they fear testing.

This does not mean post-accident drug testing is prohibited. OSHA explicitly states that testing is appropriate when there is a reasonable basis to believe that drug or alcohol use may have contributed to the reported injury or illness. The problem is automatic, blanket testing triggered by the simple fact that an injury occurred, with no analysis of whether impairment could have been a factor.

An employee who reports a repetitive strain injury from months of ergonomic exposure cannot plausibly be tested on the theory that drug use caused the injury. An employee involved in a forklift collision at the end of a shift can be tested, because impairment is a plausible contributing factor and the circumstances support a reasonable basis for testing.

Your post-accident drug testing policy needs to include the “reasonable basis” standard explicitly. A policy that says “all work-related injuries will result in a drug test” is the version OSHA will cite. A policy that says “post-accident testing is required when a supervisor has reasonable grounds to believe that drug or alcohol use may have contributed to the incident” is defensible.

Update that language now, before you have an incident. The OSHA 300 Log and post-accident investigation process are covered separately in the incident investigation guide and the OSHA 300 log recordkeeping guide.

Non-DOT Employer Testing: What You Can and Can’t Do

Outside of federally mandated testing, employers generally have broad discretion to establish drug testing programs. But “generally” is doing a lot of work in that sentence, because state law variation is significant.

Employer testing programs typically include some combination of pre-employment testing before a job offer is finalized, random testing for safety-sensitive or all employees, post-accident testing subject to the reasonable basis requirement above, and reasonable suspicion testing based on documented supervisor observations.

State laws restrict several of these. New York, New Jersey, California, Montana, Minnesota, and a growing number of other states restrict or prohibit pre-employment testing for marijuana specifically. Some states require employers to offer rehabilitation before terminating an employee for a first positive result. A few states prohibit random testing for employees in non-safety-sensitive positions. These restrictions do not apply to DOT-covered positions, but they do apply to the rest of your workforce.

Before building or updating your drug testing policy, verify the applicable state law for every state where you have employees. A policy written for a Texas operation may create liability in a California location.

Marijuana and Safety-Sensitive Work

The expansion of state marijuana laws does not change the federal testing framework for DOT-covered employees. Period. A commercial driver who tests positive for marijuana metabolites under FMCSA testing has a DOT violation regardless of whether they consumed marijuana legally under their state’s law. The DOT has issued guidance on this repeatedly, most recently in 2021, and the position has not changed.

For non-DOT employers, the marijuana question is more complicated. Even in states with broad employee protections for off-duty marijuana use, employers generally retain the right to prohibit use for positions where impairment creates a safety risk. Courts in most states have upheld termination for a positive marijuana test in safety-sensitive roles even under state legalization statutes.

The practical challenge is that current urine-based testing for marijuana metabolites measures prior use, not current impairment. An employee who used marijuana two weeks ago may still test positive. Some employers in safety-sensitive industries have moved to oral fluid testing for marijuana, which has a shorter detection window and better correlates to recent use. Oral fluid testing is now authorized under the DOT’s regulations for FMCSA-covered employees as of 2024.

Drug-Free Workplace Programs and EAPs

OSHA encourages employers to approach substance abuse as a safety and health issue rather than purely a disciplinary one. Employee Assistance Programs (EAPs) that provide confidential access to counseling and treatment referrals are the tool OSHA points to in its drug-free workplace guidance.

A testing program paired with an EAP creates a path where an employee who tests positive, particularly a long-tenured employee with an otherwise strong record, can access treatment, complete a return-to-work process, and come back to work rather than simply being terminated. This approach is not required outside of specific DOT return-to-duty processes, but it aligns with OSHA’s stated preference and supports a safety culture that treats employees as people rather than liabilities.

For DOT-covered employees, the SAP process effectively mandates a version of this: evaluation, treatment or education, and a structured return to duty.

What Your Policy Needs to Say

The most common policy failure is the blanket post-accident drug testing trigger. If your policy requires testing after any workplace injury without the reasonable basis standard, you have a policy that OSHA’s 2016 rule was specifically written to address. That is the piece most employers get wrong because the older model of “any injury triggers testing” seemed like it reduced liability. Under the current framework, it creates it.

The fix is a single sentence. Add language requiring a supervisor to document specific circumstances that provide reasonable grounds to believe impairment may have contributed to the incident before initiating post-accident testing. That documentation protects you, protects the employee’s right to report injuries without fear of automatic testing, and puts your policy on the right side of OSHA’s anti-retaliation requirements.

The employer training requirements tied to drug testing policies are covered in the employer safety training requirements guide.