What Can Cause a False Positive for Methadone

Methadone is an opioid (narcotic) drug that is used to relieve pain, and to help decrease and manage the withdrawal symptoms of other opioids, such as heroin. Methadone works through binding to the same receptors in the brain, through which other opioids affect, including μ (mu) and k (kappa) receptors.

That’s why Methadone is used as a substituent to help people get rid of addiction to other opioids. Also, that’s why Methadone is amongst the commonly-abused and misused for recreational purposes.

What Can Cause a False Positive

  • Quetiapine-containing drugs, such as Seroquel
  • Thioridazine- containing drugs, such as Thorazine
  • Doxylamine-containing drugs, such as Unisom
  • Verapamil-containing drugs, such as Calan
  • Chlorpromazine-containing anti-psychotics, such as Thorazine
  • Clomipramine-containing drugs, such as Anafranil
  • Diphenhydramine-containing drugs, such as Allergy Relief, Allermax, Banophen, Benadryl, Compoz Nighttime Sleep Aid, Diphedryl, Diphenhist, Dytuss, Nytol QuickCaps, Q-Dryl, Quenalin, Scot-Tussin Allergy Relief Formula, Simply Sleep, Sleepinal, Sominex, Tranquil, Twilite, Unisom Sleepgels Maximum Strength, Valu-Dryl, Vanamine PD, Z-Sleep and ZzzQuil

Why do those drugs cause a false positive

The majority of drug tests detect Methadone in the system through certain types of assays, which sometimes are not able to specifically detect Methadone. Instead, those tests work, depending on a structure-based technique that detects not only Methadone-containing drugs, or Methadone metabolites; but also all drugs having structures similar to those of Methadone and Methadone’s metabolites, causing a false positive for Methadone.

Factors That Affect False Positive for Methadone

As long as those drugs or their metabolites are still in your system, they are likely to cause a false positive for methadone.

Importantly, other factors can significantly affect the false positive results of Methadone’s tests. Those factors differ from a person to another, including:

  • your age
  • your body mass
  • The administered dosage. For example, in case you administer an overdose of any of the previously-mentioned drugs, it will undoubtedly take your system a long time to be cleared.
  • Whether you’re a light or a chronic user of the previous drugs.
  • Your metabolic rate of drugs, which determines how quickly your body can get rid of those drugs. Your metabolic rate depends mainly on how much your liver and kidneys are functioning properly.
  • The type of tests you are required to undergo, as well as the time the test is performed. Each test has a certain time frame to detect certain drugs.


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