Missouri does not have a single, general statute that tells private employers when they may or must drug test. There is no state licensing scheme for a workplace drug testing program the way some states run one for premium discount purposes. Instead, Missouri employer obligations come from three separate places in state law: the marijuana provisions in the Missouri Constitution, the workers compensation statute that reduces or forfeits benefits tied to intoxication, and the unemployment statute that defines when a positive test counts as misconduct. Federally regulated employers layer 49 CFR Part 40 on top of all of it. This post walks through each piece and cites the primary source for every rule described.
Missouri Has No General Private Employer Drug Testing Statute
Unlike states that regulate exactly how a private employer must collect a specimen, notify an employee, or confirm a positive screen before it can be used, Missouri has not enacted a comparable general drug testing statute for private sector employers outside of the unemployment and workers compensation contexts described below. Because the rule in any given area can shift as the legislature or courts act, employers should verify current requirements directly on the Missouri Revisor of Statutes portal rather than relying on a summary, and confirm agency guidance on labor.mo.gov before finalizing a policy.
What This Means in Practice
Employers generally set their own testing circumstances (pre employment, random, reasonable suspicion, post accident) through a written policy, subject to the constitutional marijuana provisions, the workers compensation statute, and the unemployment statute discussed below. A written, consistently applied policy also matters because it is a prerequisite for the unemployment misconduct rule to apply at all.
Article XIV and Marijuana in the Workplace
Missouri voters added medical marijuana protections to the state constitution in 2018 and expanded the law to adult use with Amendment 3 in 2022. Both sets of provisions live in Article XIV, Section 1 of the Missouri Constitution. The article gives qualifying patients and adults certain rights to possess and use marijuana, but it does not take away an employer's ability to run a drug free workplace.
The constitutional text specifically protects an employer's right to prohibit an employee from being under the influence of marijuana while at work and to discipline an employee, up to and including termination, for working or attempting to work while under the influence. It also states that a person cannot bring a wrongful discharge, discrimination, or similar claim against an employer, former employer, or prospective employer based on the employer enforcing that kind of policy. Article XIV does not require an employer to accommodate the use, consumption, possession, transfer, display, transportation, sale, or growing of marijuana in a place of employment, and it does not create any criminal or civil immunity for being under the influence while operating a vehicle, aircraft, or other dangerous equipment.
What Article XIV does not spell out in detail is exactly how "under the influence" must be proven for workplace discipline in every circumstance, and Missouri courts and agencies continue to interpret edge cases. Where a specific fact pattern is not addressed in the text of Article XIV, treat the rule as varying and confirm current interpretation through the Missouri Revisor of Statutes portal linked above before disciplining an employee based solely on a positive marijuana result.
Workers Compensation Benefit Reduction and Forfeiture
Missouri's workers compensation law, RSMo 287.120, addresses what happens to benefits when alcohol or a nonprescribed controlled substance is involved in a workplace injury. Under the statute, compensation and death benefits are reduced by fifty percent if the injury was sustained in conjunction with the use of alcohol or a nonprescribed controlled substance in violation of the employer's rule or policy. If the use of alcohol or a nonprescribed controlled substance is found to be the proximate cause of the injury, benefits can be forfeited entirely rather than merely reduced.
The statute also creates a rebuttable presumption: voluntary use of alcohol to a level that would constitute legal intoxication under Missouri law gives rise to a presumption that the alcohol use was the proximate cause of the injury, and the employee carries the burden to rebut that presumption by a preponderance of the evidence. An employee's refusal to submit to a chemical test can also affect the forfeiture analysis under the statute.
Why Post Accident Testing Still Matters in Missouri
Because RSMo 287.120 ties benefit reduction and forfeiture directly to a documented positive test or a documented refusal, a post accident testing step in the written policy is what gives the employer the evidence needed to invoke the reduction or forfeiture provisions in a workers compensation claim. Without a test result in the record, an insurer or administrative law judge has nothing to apply the statute to.
Unemployment Disqualification After a Positive Test
RSMo 288.045 governs whether a positive drug or alcohol test supports a finding of misconduct for unemployment purposes. Under the statute, if a claimant is at work with a detectable amount of alcohol or a controlled substance in their system, in violation of the employer's alcohol and controlled substance workplace policy, that is treated as misconduct connected with the claimant's work. The statute also treats a refusal to test, or an attempt to adulterate or impede test results, as misconduct.
The misconduct finding depends on the employer having a written policy that the employee was actually notified of, through conspicuous workplace posting, a written personnel policy or handbook, or a collective bargaining agreement, and that policy must state that a positive result may lead to suspension or termination. Employers who start a new testing policy after the statute's effective date must also allow at least sixty days between the general notice to employees that a program is being implemented and the date the program actually takes effect. The statute carves out use of a controlled substance taken under and in conformity with the lawful order of a health care practitioner, which is not treated as misconduct.
Federally Regulated and Safety Sensitive Positions
None of the state provisions above override federal testing law for a safety sensitive position covered by the Department of Transportation. Drivers, pilots, and other DOT covered employees remain subject to 49 CFR Part 40, including its own collection, chain of custody, and medical review officer verification requirements, regardless of what state marijuana law otherwise permits. Missouri's constitutional marijuana provisions do not change what a DOT regulated employer must do for a covered position.
Building a Missouri Compliant Testing Policy
A written policy is the common thread running through every piece of Missouri law covered above. It is what lets an employer invoke the workers compensation reduction or forfeiture rule, it is what a claims deputy checks before disqualifying a claimant for unemployment, and it is what Article XIV assumes exists when it protects an employer's right to discipline for impairment. A defensible policy generally states the categories of testing used, references the substances tested, explains the consequences of a positive result or a refusal, and routes every non negotiated result through confirmation and a medical review officer before any employment action is taken on a prescribed medication result.
Employers evaluating cup, dip card, or oral fluid formats for a Missouri workforce can review the drug test cup collection for panel options that support a documented, consistently applied program. For employers weighing whether a formal program could also affect workers compensation insurance pricing, the article on workers comp drug testing premium discounts covers how state programs elsewhere approach that question, since Missouri's own reduction and forfeiture rule under RSMo 287.120 works differently from a premium discount program. Employers operating in more than one state should also see the roundup on marijuana legalization and workplace drug testing for how other legal marijuana states handle the same employer questions.
| Law | What it covers | Employer takeaway |
|---|---|---|
| Article XIV, Section 1, Missouri Constitution | Medical and adult use marijuana, employer discipline rights | No duty to accommodate on the job use or impairment; discipline for being under the influence is protected from wrongful discharge claims |
| RSMo 287.120 | Workers compensation benefit reduction and forfeiture | Fifty percent reduction, or full forfeiture if use was the proximate cause, tied to a documented positive test or refusal |
| RSMo 288.045 | Unemployment insurance misconduct standard | Positive test counts as misconduct only with a written, properly noticed policy and a certified lab result; prescribed medication is excepted |
| 49 CFR Part 40 | Federal DOT testing procedures | Applies to safety sensitive positions regardless of state marijuana law |
Frequently asked questions
Does Missouri require private employers to drug test?
No. Missouri does not have a general statute that requires private employers to run a drug testing program. Testing is generally left to the employer's own written policy, subject to the constitutional, workers compensation, and unemployment provisions described above.
Can a Missouri employer discipline an employee for being under the influence of marijuana at work?
Article XIV of the Missouri Constitution protects an employer's ability to prohibit an employee from being under the influence of marijuana at work and to discipline the employee for it, and it states that this kind of discipline does not create a wrongful discharge or discrimination claim. Employers should still apply any impairment based policy consistently and document the basis for the decision.
Does a positive drug test always reduce workers compensation benefits in Missouri?
Under RSMo 287.120, a positive test connected to a workplace injury can lead to a fifty percent benefit reduction, and full forfeiture if the use is found to be the proximate cause of the injury. The exact outcome depends on the facts of the claim and the evidence in the record, so employers should not assume automatic forfeiture without documentation.
What makes a positive test count as misconduct for Missouri unemployment purposes?
RSMo 288.045 requires a written alcohol and controlled substance policy that the employee was actually notified of, a certified lab test, and no valid prescription explanation. Without a properly noticed written policy, a positive result may not support a misconduct disqualification.
Do DOT drug testing rules still apply in Missouri even though marijuana is legal there?
Yes. Safety sensitive positions covered by the Department of Transportation remain subject to 49 CFR Part 40 regardless of Missouri's marijuana laws, since federal testing rules for those positions are not changed by state constitutional provisions.
Where can a Missouri employer confirm the current text of these laws?
The Missouri Revisor of Statutes portal publishes the current text of RSMo 287.120, RSMo 288.045, and Article XIV of the Missouri Constitution, and labor.mo.gov publishes related unemployment guidance. Because legislative and agency language can change, employers should check those sources directly rather than relying on a summary.
This article is general information about Missouri law as of the date of publication and is not legal advice. Employers should consult qualified counsel before adopting or enforcing a drug testing policy.
