What Can Cause a False Positive for Amphetamine

Amphetamines are a group of highly addictive drugs that include, for example, Dextroamphetamine, Levoamphetamine, Lisdexamfetamine, and Methamphetamine. Amphetamines are, generally, stimulants of the central nervous system.

Amphetamines are indicated to treat three disorders, including attention deficit hyperactivity disorder (ADHD), narcolepsy and resistant obesity. Amphetamines modulate the levels of 4 hormones, including serotonin, norepinephrine, dopamine, and acetylcholine.

Because of amphetamines’ positive effects on performance, fatigue, and mood, amphetamines are commonly addicted. Evekeo, Adzenys XR-ODT, Adderall and Dyanavel XR are examples of common amphetamines-containing drugs.

What DrugsĀ  Cause a False Positive

  • Amantadine
  • Diet pills
  • Ritodrine
  • Selegiline
  • Trimethobenzamide
  • Trimipramine
  • Some anti-depressants, including: Desipramine, Trimipramine, Bupropion, Trazodone and Fluoxetine.
  • Drugs similar to amphetamines, including Benzphetamine and Phentermine
  • Chlorpromazine-containing anti-psychotics
  • Some 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 For Amphetamine

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

How long can those drugs cause a false positive

As long as those drugs or their metabolites are still in your system, they are likely to cause a false positive amphetamine. So, the proper question should be:


Amantadine is an antiviral drug used for treating Parkinsonism, and as a prophylactic vaccine for flu. Up to more than 3.5 days post-administration, Amantadine can likely stay in your system, as amantadine has an average half-life of 10-14 hours.


Benzphetamine is a drug similar to dextroamphetamine. Benzphetamine is used for obesity. Examples of Benzphetamine-containing brands include Didrex and Regimex.

Research shows that the half-life of Benzphetamine is around 16-31 hours; while other research shows the half-life to be around 6-12 hours. Therefore, up to more than 7.75 days or 3 days, respectively post-administration, Benzphetamine-containing drugs can stay in your system.


Phentermine is a drug indicated to treat obesity. Examples of common drugs containing phentermine include Adipex, Fastin, Ionamin, Adipex-P, Oby-Cap, Suprenza, T-Diet and Zantryl.

Up to more than 7.75 days post-administration, phentermine-containing drugs can stay in your system. The reason is that the half-life of phentermine is around 16-31 hours.

Diet Pills

Diet pills are commonly referred to as ‘weight loss pills.’ Those pills include a broad range of ingredients and drugs, such as orlistat, phentermine, herbal remedies, and methamphetamine. Thus, to determine how long the diet pills you take can cause a false positive amphetamine, it is a must first to determine what ingredients are contained in those pills?


Desipramine is an antidepressant ingredient. Norpramin is an example of the common brands containing Desipramine. Because of the long half-life of Desipramine that starts from 7 hours and extends to 60+ hours, up to more than 15 days post-administration, Desipramine-containing drugs can stay in your system.


Ritodrine is a relaxing drug used for the uterus, especially to prevent premature labor. Ritodrine has a half-life of 1.7-2.6 hours. Therefore, up to more than 15.6 hours post-administration, Ritodrine can stay in your system.


Selegiline is a drug used in patients with Parkinson’s disease. Eldepryl is a common example of the brands containing Selegiline. The half-life of Selegiline ranges from 1.2 to 2 hours. Thus, within 12-hours duration post-administration, selegiline-containing drugs can stay in your system.


Trimethobenzamide is an anti-emetic drug that has a half-life of 7-9 hours. Therefore, up to 2.25 days post-administration, Trimethobenzamide can stay in your system.


Trimipramine is an antidepressant drug belonging to a category known as tricyclic anti-depressants. Trimipramine has a half-life of 11-18 hours. Thus, up to 4.5 days post-administration, Trimipramine can stay in your system.


Bupropion is an antidepressant drug used to help lose weight, ease smoking cessation, as well as treating two types of depression, including major depressive disorder and seasonal affective disorder. Examples of drugs containing Bupropion: Aplenzin, Forfivo XL, Wellbutrin SR, and Zyban.

For five days post-administration or longer, Bupropion can stay in your system; 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 can stay in your system.


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 can stay in your system.


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 days. Therefore, up to 96 days post-administration, fluoxetine-containing drugs can stay in your system.


Chlorpromazine is an anti-psychotic drug used to treat different issues, such as mania, some stomach-related issues, and schizophrenia. Chlorpromazine has an approximate half-life of 30 hours, which means that up to 7.5 days post-administration, Chlorpromazine can stay in your system.

Ephedrine nasal inhaler

Ephedrine is a nasal decongestant that is taken to treat three issues, including difficulty in a breath, a stuffy nose, and wheezing. Up to 1.5 days post-administration, ephedrine can stay in your system.


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 Cutrim 16 Hour, Acutrim II, Maximum Strength, Control, Dexatrim and Empro.

The half-life of phenylpropanolamine ranges from 2.1 to 3.4 hours. Therefore, up to 20.4 hours post-administration, phenylpropanolamine-containing drugs can stay in your system.


Promethazine is an anti-histaminic drug used for treating 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 post-administration, promethazine-containing drugs can stay in your system.


Brompheniramine is also an antihistaminic drug commonly prescribed for symptoms of colds and flu, such as a runny nose, watery eyes, and itching.

For 8.55 days post-administration, brompheniramine can stay in your system, 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, Entex and Genaphed.

The half-life of pseudoephedrine is around 9-16 hours. Thus, up to 4 days post-administration, pseudoephedrine-containing drugs can stay in your system


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 can stay in your system for 18.6 hours, post-administration.


Metformin is an anti-diabetic ingredient indicated to treat type 2 diabetes mellitus. Fortamet, Glucophage, and Riomet are examples of common drugs containing metformin.

As the half-life of metformin is around 8-12 hours, metformin-containing drugs can stay in your system for up to 3-days, post-administration or longer.


Labetalol is a drug indicated to manage blood pressure. Trandate is a common example of Labetalol-containing drugs.

The half-life of labetalol is around 6-8 hours, which makes Labetalol-containing drugs stay in your system for two days post-administration.


Methylphenidate is a stimulant of the central nervous system. Methylphenidate is used to treat narcolepsy, attention deficit disorder (ADD), and attention deficit hyperactivity disorder (ADHD). Examples of common drugs containing methylphenidate: Ritalin, Aptensio XR, Concerta, Cotempla XR-ODT, and Metadate CD.

Up to 48 hours post-administration, methylphenidate or Ritalinic acid can stay in your system.

Other factors affect false-positive tests of Amphetamine

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

  • Your age
  • Your body mass
  • The administered dosage. For example, an overdose of any of the previously-mentioned drugs undoubtedly takes a longer time to be cleared from the body.
  • 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. For example, in case you have renal insufficiency, Amantadine’s half-life becomes 7-10 days, resulting in prolonging the time Amantadine stays in your system for up to 2 months post-administration.
  • 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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