What Can Cause a False Positive for Meth

Meth is an abbreviation of Methamphetamine, which is a drug prescribed to treat three issues, including attention deficit hyperactivity disorder (ADHD), narcolepsy and resistant obesity. Meth works through its stimulatory effects on the central nervous system, increasing the levels of 3 hormones in the brain, including norepinephrine, dopamine, and serotonin.

That, in turn, results in improving performance, decreasing fatigue, and giving a feeling of high-mood. That’s why Meth is commonly abused and misused for recreational purposes. Meth is also commonly known as Crystal meth, Crank, Meth, Ice, Glass, Fire, Crypto, Speed and Chalk.

What Can Cause a False Positive For Meth

Many drugs can cause a false positive for Meth, as shown below.

  • Anti-depressants, including Bupropion, Trazodone, and Fluoxetine.
  • Chlorpromazine-containing anti-psychotics
  • Decongestants and anti-histaminic drugs, including Ephedrine nasal inhaler, Phenylpropanolamine, Promethazine, Brompheniramine, and Pseudoephedrine.
  • Ranitidine
  • Metformin-containing anti-diabetics
  • Labetalol-containing drugs
  • Methylphenidate-containing drugs

Why do those drugs cause a false positive

The majority of drug tests detect Meth in the system through certain types of assays, which sometimes are not able to specifically detect Meth itself. Instead, those tests, depending on a structure-based technique, detect not only Meth-containing drugs; but also all the drugs having structures similar to those of Meth, resulting in a false positive for Meth.

So, in case you’re administering one or more of those drugs, you need to ensure taking the proper precautions into considerations or to tell the testing lab about all those drugs.

How long can those drugs cause a false positive

The duration each of those drugs can cause a false positive for Meth differ from a drug to another, and even from a person to another, as follow:


Bupropion is an antidepressant drug prescribed for two main types of depression, including major depressive disorder and seasonal affective disorder. Also, Bupropion is prescribed for weight loss and for easing smoking cessation. Examples of drugs containing Bupropion: Aplenzin, Forfivo XL, Wellbutrin SR, and Zyban.

For five days post-administration or longer, Bupropion is likely to show up on drug tests, causing a false positive for Meth; while the other substances resulting from Bupropion metabolism in the body, including hydroxybupropion,erythrohydrobupropion, and threohydrobupropion, have a half-life of 20 hours, 33 hours, and 37 hours, respectively.

Therefore, up to 5 days, 8.25 days, and 9.25 days, respectively, those metabolites are likely to cause a false positive for Meth.


Trazodone is an antidepressant drug indicated to treat the major depressive disorder. Oleptro, Desyrel and Desyrel Dividose are examples of common brands containing Trazodone. The half-life of Trazodone ranges initially from 3 to 6 hours and finally from 5 to 9 hours. Therefore, up to 2.25 days or longer post-administration, Trazodone containing drugs are likely to cause a false positive for Meth.


Fluoxetine is also an antidepressant drug. Prozac, Sarafem, and Rapiflux are three examples of common brands containing fluoxetine. The half-life of norfluoxetine that results from fluoxetine is around 4-16. Therefore, up to 96 days or longer post-administration, fluoxetine-containing drugs are likely to cause a false positive for Meth.


Chlorpromazine is an anti-psychotic drug used to treat different issues, such as mania, an upset stomach, and schizophrenia. Chlorpromazine has an approximate half-life of 30 hours, which means that up to 7.5 days post-administration, Chlorpromazine can likely cause a false positive for Meth.

Ephedrine nasal inhaler

Ephedrine is a nasal decongestant that is taken to treat three common issues, including difficulty in a breath, a stuffy nose, and wheezing. Up to 1.5 days or longer postadministration, ephedrine can likely cause a false positive for Meth.


Phenylpropanolamine is a nasal decongestant used for treating the congestion resulting from hay fever, allergy, colds, and flu. Common names of drugs containing phenylpropanolamine include trim 16 Hour, Acutrim II, Maximum Strength, Acutrim Late Day, Control, Dexatrim and Empro.

The half-life of phenylpropanolamine ranges from 2.1 to 3.4 hours. Therefore, up to 20.4 hours or longer post-administration, phenylpropanolamine-containing drugs are likely to cause a false positive for Meth.


Promethazine is an anti-histaminic drug used for treating the flu-associated symptoms, such as watery eyes, runny nose, and itching. Phenergan is an example of the common brands containing promethazine. The half-life of promethazine is around 16-19 hours, which means that up to 4 days or longer post-administration, promethazine-containing drugs are likely to cause a false positive for Meth.


Brompheniramine is an antihistaminic drug commonly prescribed for symptoms of colds and flu, such as a runny nose, watery eyes, itching, and sneezing. For 8.55 days post-administration or longer, brompheniramine is likely to cause a false positive for Meth, as the half-life of brompheniramine is around 24.9 +/- 9.3 hours.


Pseudoephedrine is a decongestant indicated to treat stuffy nose and sinus congestion. Common examples of drugs containing pseudoephedrine include Contac Cold, Drixoral Decongestant Non-Drowsy, Elixsure Decongestant, Entex, and Genaphed. The half-life of pseudoephedrine is around 9-16 hours. Thus, up to 4 days or longer post-administration, pseudoephedrine-containing drugs are likely to cause a false positive for Meth.


Ranitidine is an antacid indicated to treat or prevent gastric ulcers, gastroesophageal reflux disease (GERD) and Zollinger-Ellison syndrome. Zantac and Taladine are two common drugs containing ranitidine. As the half-life of ranitidine is around 2.8-3.1 hours, ranitidine-containing drugs are likely to cause a false positive for Meth within an 18.6-hours duration or longer, postadministration.


Metformin is an anti-diabetic ingredient indicated to treat type 2 diabetes mellitus. Metformin is contained in 5 common drugs, including Fortamet, Glucophage, Glucophage XR, Glumetza and Riomet. As the half-life of metformin is around 8-12 hours, metformin-containing drugs are likely to cause a false positive for Meth within a 3-days duration, post-administration or longer.


Labetalol is an ingredient indicated to manage blood pressure. Trandate is a common example of the drugs containing Labetalol. The half-life of labetalol is around 6-8 hours, which makes Labetalol-containing drugs are likely to cause a false positive for Meth within two days or longer postadministration.


Methylphenidate is a stimulant of the central nervous system. It is indicated to treat narcolepsy,  attention deficit disorder (ADD), and attention deficit hyperactivity disorder (ADHD). Examples of drugs containing methylphenidate: Ritalin, Aptensio XR, Concerta, Cotempla XR-ODT, and Metadate CD. Up to 48 hours or longer post-administration, methylphenidate or Ritalinic acid, respectively, are likely to cause a false positive for Meth.

Other factors affect false-positive tests of Meth

Importantly, other factors can significantly affect the results of Meth’s tests.

Those factors differ from a person to another, including:

  • Your age
  • Your body mass
  • The administered dosage. For example, an overdose undoubtedly takes a longer time to be cleared from the body.
  • Whether you’re a light or a chronic user of the previously mentioned drugs.
  • Your metabolic rate of drugs, which determines how quickly your body can get rid of those drugs.
  • 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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