Yes, in most cases you can retake a drug test, but the route depends on who’s testing you. If you’re covered by U.S. Department of Transportation (DOT) rules, you have a specific right to request that a preserved backup portion of your original sample be tested at a second certified laboratory, and you have 72 hours from notification of a verified positive to ask for it.1eCFR. 49 CFR 40.171 If you work for a private employer outside DOT-regulated industries, whether you can retest and on what terms comes down to the company’s written drug testing policy and your state’s laws.
The 72-Hour Split Specimen Retest
Every urine collection under DOT rules is a split collection. The collector pours at least 30 mL into a primary bottle and at least 15 mL into a second bottle.2U.S. Department of Transportation. 49 CFR 40.71 – How Does the Collector Prepare the Urine Specimen The second bottle exists for exactly one reason: if the primary comes back positive, you can have that backup tested at a different certified lab.
The clock starts when the Medical Review Officer (MRO) notifies you of a verified positive result, or of a refusal based on adulteration or substitution. You have 72 hours to ask. The request can be verbal or written. Miss the window because of serious illness, injury, an inability to reach the MRO, or another unavoidable circumstance, and you can present that documentation to the MRO, who may still authorize the test.1eCFR. 49 CFR 40.171
Who Pays
Your employer must send the split specimen for testing once you make a timely request. The employer cannot refuse, delay, or condition the test on you paying upfront. Cost is not allowed to be the barrier. That said, the employer can seek reimbursement from you afterward through a written company policy or collective bargaining agreement. The federal rule takes no position on who ultimately bears the cost.3US Department of Transportation. 49 CFR Part 40 Section 40.173
What Happens If the Second Lab Doesn’t Confirm
If the second laboratory fails to reconfirm the original positive, the MRO must cancel the test entirely and report the cancellation to both the employer and to the DOT’s Office of Drug and Alcohol Policy and Compliance. In certain narrow situations, such as when substitution criteria aren’t met and creatinine sits in a borderline range, the MRO may direct an immediate recollection under direct observation. Otherwise, the original positive does not stand.4eCFR. 49 CFR 40.187 – What Does the MRO Do With Split Specimen Results
Talk to the MRO Before You Ask for a Retest
No positive result becomes official until it passes through a Medical Review Officer, a licensed physician who evaluates whether a legitimate medical reason explains the result. The MRO will call you to discuss the findings and ask about prescription medications. This conversation is where most false positives from legitimate prescriptions get resolved, and it happens before you’d need to invoke the split specimen right.
If a prescribed medication could account for the result, the MRO must verify it independently. That means calling your pharmacy to confirm the prescription is authentic and, if questions remain, contacting your prescribing physician. A photo of a pill bottle label is not accepted as proof. If you need to sign a release so your pharmacy can share information, act on that request immediately.5US Department of Transportation. Back to Basics for Medical Review Officers
For adulterated or substituted specimens, more falls on you. You must show that the abnormal finding has a physiological explanation. The MRO can give you up to five additional days to gather medical evidence if there’s a reasonable basis to believe you can produce it, and may refer you to a specialist for further evaluation before making a final determination.6eCFR. 49 CFR 40.145
Substances That Commonly Trigger False Positives
Initial screening uses immunoassay technology, which is fast but not perfectly specific. Some common culprits worth raising with the MRO:
- Pseudoephedrine and phenylephrine, found in cold and sinus medications, can flag for amphetamines.
- Ibuprofen and naproxen have been associated with false positives for barbiturates and, less commonly, cannabinoids.
- Dextromethorphan, a cough suppressant in many over-the-counter products, can trigger screens for opiates or PCP.
- Poppy seeds contain trace amounts of morphine and codeine. Federal guidelines raised the opiate screening cutoff specifically to reduce poppy seed false positives, but large quantities can still cause problems.
- Proton pump inhibitors such as omeprazole have been linked to false positives for cannabinoids on some screening platforms.
Confirmatory testing using gas chromatography-mass spectrometry identifies the specific molecular structure of the substance and eliminates most cross-reactivity. If the initial screen is positive but confirmatory testing doesn’t detect the specific drug, the result is reported as negative.
When a New Collection Is Ordered Automatically
Some situations produce a second collection without any request from you. This isn’t a second chance in the sense of appealing a bad result; it’s built into the process when something about the sample is off.
Temperature Out of Range
A urine specimen must register between 90°F and 100°F when the collector checks it within four minutes of collection. If it falls outside that window, the collector immediately conducts a new collection under direct observation or collects an oral fluid specimen instead. Both original and new specimens go to their respective laboratories for testing. Refusing to provide the second specimen counts as a refusal to test.7US Department of Transportation. DOT Rule 49 CFR Part 40 Section 40.65
Invalid Result
A lab sometimes reports a result as invalid, meaning the specimen couldn’t be tested reliably. The MRO consults with the lab’s certifying scientist and then contacts you to ask whether any medication could explain the abnormal specimen. An acceptable explanation cancels the test with no further collection needed, unless it was a pre-employment, return-to-duty, or follow-up test requiring a negative result. If you can’t explain it but deny tampering, the MRO directs your employer to collect a new specimen under direct observation immediately.8eCFR. 49 CFR 40.159 – What Does the MRO Do When a Drug Test Result Is Invalid
Dilute Specimen
Drinking a lot of water before a test can produce a dilute specimen. The response depends on the underlying result. On a negative-dilute with creatinine above 5 mg/dL, your employer has the option, but not the obligation, to send you for another test. Creatinine between 2 and 5 mg/dL prompts the MRO to direct an immediate recollection under direct observation. A positive-dilute is simply treated as a verified positive; your employer cannot order a retest of a positive result on the ground that the specimen was dilute.9US Department of Transportation. 49 CFR 40.197 – What Happens When an Employer Receives a Report of a Dilute Urine Specimen
Refusing Is Not a Way Out
Under DOT regulations, refusing a test carries the same consequences as testing positive. Refusal covers more than saying no. It includes failing to show up within a reasonable time after being directed to test (except for pre-employment tests), leaving the collection site before the process is complete, failing to provide a specimen without an adequate medical explanation, refusing direct observation when required, not cooperating with the collection process, declining an additional test the employer has directed, and not completing a required medical evaluation.10eCFR. 49 CFR 40.191 Walking away from the test to avoid a bad result closes the door on the split specimen retest, because there is no split specimen to test.
If You’re Not Covered by DOT Rules
Everything above applies to federally regulated testing under DOT rules, which covers transportation workers, nuclear energy employees, and other safety-sensitive positions. If you work for a private employer outside those industries, the landscape is less uniform and often less protective.
Private employers generally design their own drug testing programs. Some mirror the DOT framework with split specimens, MRO review, and confirmatory testing. Others use simpler processes. Whether you can request a retest, how long you have to do so, and who pays for it all depend on the employer’s written policy and the laws of your state. Some states require certified laboratories and give employees a chance to explain positive results before adverse action. Others impose almost no procedural requirements.
A few practical steps apply either way:
- Ask for the drug testing policy in writing. If your employer has one, you’re usually entitled to see it. Read it before you’re in a situation where you need to challenge a result.
- Document your prescriptions. If you take any medication that could trigger a positive screen, having prescription information ready to present saves time and reduces the chance of an incorrect final result.
- Act fast. Whether the window is 72 hours or defined by company policy, delays almost always work against you.