Positive Drug Tests

Why Positive Drug Tests Aren’t Always the End of the Road

As you will learn in the course of your DOT urine collection certification, urine drug tests occasionally come back positive even though the donor isn’t using any illicit drugs. Sometimes, the drug tests pick up other prescription medications making it appear as if the driver is not fit to drive commercially. However, these false positives can have a valid, legal explanation. So, a positive test isn’t always the end of the road for a commercial driver. Let’s take a deeper dive into what may cause a false positive result and what happens when they occur.

When a Urine Sample Drug Test is Collected

Urine sample drug tests look for illicit habit-forming drugs that could impair a driver’s ability to drive safely. These are Department of Transportation and employer-mandated screenings that can be required under the following circumstances:

  • Part of the new-hire process
  • Part of a random drug testing protocol
  • If the employee’s behavior, demeanor, or smell gives an employer reasonable cause to suspect the employee is under the influence
  • After an accident, to prove the employee was sober
  • As a follow-up after a positive drug test

What the Drug Test Looks For

  • Benzodiazepines
  • THC (Tetrahydrocannabinol) is present in recreational cannabis
  • Illegal opioids like heroin
  • Prescription-only opioids, including oxycodone and morphine
  • Phencyclidine (PCP)
  • Cocaine
  • Amphetamines like Adderall and Meth
  • Barbiturates

Some drug tests look for a specific medication, including:

  • Lysergic acid diethylamide (LSD)
  • Tramadol
  • Fentanyl
  • Methylenedioxymethamphetamine (MDMA or ecstasy)
  • Methadone

How False Positives Happen

Occasionally, there’s a false positive. It could be due to laboratory errors but is usually caused by another medication. For example:

  • Dextromethorphan, an ingredient in cough medicines, tests as PCP
  • Diphenhydramine, an ingredient in antihistamines, tests as an opioid
  • Pseudoephedrine, an ingredient in nasal decongestants, tests as an amphetamine or methamphetamine
  • Phentermine, an appetite suppressant, tests positive for amphetamines
  • Quetiapine, a medication that treats schizophrenia, bipolar disorder, and major depressive disorder, tests as an opioid
  • Proton pump inhibitors, which reduce the production of stomach acid, test as THC
  • Promethazine, used to treat insomnia, allergies, and nausea, can test as amphetamine or methamphetamine
  • Non-steroidal anti-inflammatory drugs (NSAIDs), like aspirin and ibuprofen, can test as THC or barbiturates
  • Quinolone antibiotics can test as an amphetamine, methamphetamine, or an opioid
  • Venlafaxine and Desvenlafaxine, antidepressants, test as PCP
  • Sertraline, an antidepressant, tests as a benzodiazepine or LSD
  • Trazodone, used to treat depression and insomnia, tests as amphetamines or methamphetamines
  • Bupropion, used to treat depression and help people quit smoking, tests as amphetamines or methamphetamines

What Happens After a Positive Drug Test

If the standard drug test comes back positive, the medical review officer (MRO) will contact the driver for an interview. They will look for another medical reason why they could have failed the drug test before any negative consequences.

Suppose the driver can provide documentation for a properly prescribed medication. In that case, they can do a split test looking specifically for that medication. This type of test can confirm that the medication in question caused the positive reading. If there is a legitimate reason for the positive result, the medical review officer reports a negative result to the driver’s employer.

Not All Explainable Positive Tests Are OK

Of course, not all explained test results mean the driver is safe to operate a commercial vehicle. There are prescription medications that could impair a driver’s ability to drive and impair their judgment. Other drugs could indicate a deeper medical issue that needs to be addressed. These conditions may not prohibit the individual from driving, but it may limit the amount of time between the driver’s DOT exams so the DOT medical examiner can monitor the driver’s condition.


Urine sample drug tests are a tool used to keep our drivers and the public safe, but no tool is foolproof. There are substances that can confuse the results, jeopardizing a driver’s career. The people running the tests, reviewing the results, and performing follow-up interviews dive deeper into the situation to prevent the tool from unfairly ending a driver’s career.

The drugs that can skew the results of the urine drug test are often an indicator of a problem that must be addressed, not necessarily disqualifiers on their own. They start the conversation between a driver and their medical examiner, who will make the final determination about their fitness to drive after a thorough investigation into the driver’s medical history and symptoms.


Why Positive Drug Tests Aren’t Always the End of the Road