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What causes false-positive drug test results?

If you have taken a chemical test because a Louisiana law enforcement officer believed you were driving under the influence of illegal substances, a positive result can have devastating consequences. When you have not been using illicit drugs, that result could be a major shock, too. Before you panic, you should know that a medication you are taking legally could have caused your false positive.


Taking medication for your mental health can increase your quality of life and make it possible for you to function normally. According to GoodRx, Inc., some of the following could also cause you to test positive for specific illegal drugs:

  • Prozac: amphetamines, methamphetamines or LSD
  • Zoloft: benzodiazepines or LSD
  • Quetiapine: methadone
  • Bupropion: amphetamines, methamphetamines or LSD
  • Amitriptyline: LSD

You should make sure the authorities have the information about your prescription antidepressants and how they may affect your drug test.

Over-the-counter medications

Many sleep aids, such as Unisom and Medi-Sleep, contain doxylamine, which can lead to a positive for PCP, opiates or methadone. More than one kind of cold medicine that you can buy without a prescription at your local pharmacy may also be the culprit. These include diphenhydramine (an antihistamine that triggers a positive for methadone or PCP) and pseudoephedrine (a decongestant that may show up as amphetamines or methamphetamines). Even ibuprofen and naproxen can cause a positive urine screen test for THC, PCP or barbiturates if you take either of these anti-inflammatory pain medications regularly.

Blood pressure control

Taking your blood pressure medication as prescribed by your doctor can save your life. Your labetalol could also cause a positive for amphetamines, methamphetamines or LSD. Diltiazem in your urine could indicate that you have been using LSD.


Your oral diabetes medication, Glucophage, can appear as amphetamines or methamphetamines in a drug test, as can Ritalin. You could also test positive for LSD if you take this medication for ADD, ADHD or narcolepsy. If you have recently taken Tramadol for pain, you are at risk for a PCP positive.

Because of the extremely harsh penalties for drug use in Louisiana, you should talk to an attorney if a law enforcement officer tells you that you must take a chemical test.

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