You challenge a cannabis drug test result by attacking the test, not the cannabis. Get the lab paperwork, request a retest of the split specimen before the deadline, and raise any medical or state law defense with the medical review officer (MRO). If the employer still acts, the next moves are a union grievance, a state agency complaint, or a lawsuit under state law.
more on this topic
Step 1: Get the Test Record in Writing
Ask HR for the full test record before you argue your case. A positive screening result is not a verified positive until a confirmation test backs it up.
can employers fire you for medical cannabis use
- The lab name and its certification.
- The collection date, the test panel, and the screening cutoff.
- The confirmation method, which should be GC-MS or LC-MS.
- The chain-of-custody form, signed and dated.
Under federal testing standards, a urine sample screens positive at 50 ng/mL of THC metabolite and confirms positive at 15 ng/mL. A result that sits close to the line is worth questioning, and so is a result reported without a confirmation run.
Cannabis Workplace Testing Laws by State 2024: A Plain Guide
Step 2: Talk to the Medical Review Officer
The MRO is a physician who reviews the lab result before your employer treats it as final. You get an interview, and that call is your first real chance to explain the finding.
- List every prescription and over-the-counter drug you take.
- Mention CBD products, since some carry enough THC to trigger a positive.
- Ask which compound the lab measured, such as the THC metabolite THC-COOH.
- Ask for the actual concentration, not just positive or negative.
If the MRO cannot reach you, the result may be reported as unverified rather than positive. Answer the phone, return the call, and take notes on what was said.
Step 3: Request a Split Specimen Retest
Most collections split the sample into an A bottle and a B bottle. The lab tests A, and B stays sealed for a retest at a second lab.
- Ask the MRO or HR how long you have to request the B bottle test.
- Make the request in writing and keep a copy.
- Confirm the retest goes to a different certified lab.
- Ask who pays. Under federal rules the employer covers the cost, while private employers set their own terms.
Under federal rules the request window is 72 hours from when you learn of the verified positive. Miss it and that option is gone. A B bottle that comes back negative voids the original result.
Step 4: Check Whether Your State Protects Off-Duty Use
A growing number of states limit what an employer can do with a positive THC test. Those limits often cover off-duty use away from the workplace, and they carve out safety-sensitive jobs and federal contractors.
- California (AB 2188) bars discrimination based on off-duty cannabis use as of January 1, 2024.
- Washington (SB 5123) restricts pre-employment cannabis testing, with exceptions for safety-sensitive roles.
- Nevada, New York, New Jersey, Connecticut, Montana, and Rhode Island have their own versions with their own exceptions.
If your state has no such law, an employer can follow its own written policy in most cases. Read that policy for how a test is triggered, who sees results, and what discipline follows.
Step 5: Does a Medical Marijuana Card Help?
A state medical cannabis card does not excuse a positive result under federal testing rules. DOT tests have no medical exception, and a card will not block a DOT violation.
State protections vary. Some medical cannabis laws shield registered patients from job discrimination, while others only protect them from criminal charges. The ADA does not cover medical cannabis because federal law classifies it as an illegal drug, though a few state courts and state disability statutes have required employers to at least discuss an accommodation.
Step 6: Appeal the Employer's Decision
Move fast, because appeal deadlines are short. Pick the path that fits your job and your state.
- Union grievance, if your contract requires just cause for discipline.
- Internal appeal, if the employee handbook lists one.
- State civil rights or labor agency complaint, if a state cannabis law applies.
- Employment lawyer consult for a possible wrongful termination claim.
- Unemployment appeal, if benefits were denied over the test.
Keep a paper trail. Save texts, emails, the policy, and every test document, because dated notes beat memory in any hearing.
How Long Does THC Stay Detectable?
Timing can support your version of events. If you used cannabis weeks before a test, or not at all, the detection window matters.
- Urine: 1 to 3 days after one use, up to 30 days with heavy daily use.
- Blood: hours to about 2 days.
- Oral fluid: hours to about 1 to 2 days.
- Hair: up to 90 days.
These ranges come from general research, so they are not proof in your case. A lab report with a concentration number tells you more than a plain positive label.
FAQ
Can secondhand smoke cause a positive test?
It can in enclosed spaces with heavy smoke, but MROs treat that claim with doubt. A low concentration near the cutoff is the pattern that supports it best.
Does CBD oil show up as THC?
Full-spectrum CBD can hold enough THC to trigger a positive. CBD isolate carries much less risk, but product labels are not always accurate. If you use CBD, keep receipts and third-party lab reports.
Can my employer test me again after a negative retest?
An employer can run another test under its own policy, but a negative B bottle kills the original result. Ordering a fresh test right after a negative retest can look like retaliation in states with off-duty protections.
Should I refuse the test?
Refusing a test counts as a positive in most cases, both under employer policy and under federal rules. If you have a real objection, raise it through the MRO or a lawyer instead of walking away.
This is general information, not legal advice. Employment rules differ by state and by contract, so talk to an employment lawyer before you sign anything or let a deadline pass.