What Can Cause a False Positive for Cocaine

Cocaine is a highly addictive drug that is commonly prescribed as an anesthetic. Cocaine administration results in euphoria, increasing physical performance, and energetic feelings, reducing fatigue, and improving mental functions.

Because of those effects, cocaine is commonly abused and misused; thus, it is counted amongst illicit drugs. Being addicting, cocaine has many different street names, including coke, C, blow, snow, and flake, while the base form of cocaine is called freebase or crack.

What Can Cause a False Positive for Cocaine

  • Coca tea
  • Cocaine-containing anesthetics
  • Bupivacaine-containing anesthetics
  • Amoxicillin
  • Ampicillin
  • Some decongestants and anti-histaminic drugs, including ephedrine nasal inhaler, phenylpropanolamine, promethazine, brompheniramine, and pseudoephedrine.

Why Do Those Drugs Cause a False Positive?

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

How Long Can Those Drugs Cause a False Positive for Cocaine?

As long as those drugs or their metabolites are still in your system, they are likely to cause false positive results for cocaine. So, the proper question should be: how long can those drugs stay in the system?

Coca tea

Coca tea is commonly consumed as an herbal tea and is also known as Mate de Cocais. The administration of coca tea is likely to cause a false positive for cocaine, as it is prepared from the leaves of the coca plant, which contains alkaloids and other stimulant ingredients from which cocaine is chemically prepared.

Cocaine-containing anesthetics

Some topically applied anesthetics contain low amounts of cocaine, which travels through the blood, resulting in the possibility of causing a false positive for cocaine during drug tests. As the half-life of cocaine is around 1 hour, cocaine-containing anesthetics can stay in your system up to 6 hours or longer post-administration.


Amoxicillin is an antibiotic used to treat many types of bacterial infections. Moxatag is an example of a common drug containing amoxicillin, which can cause a false positive for cocaine. Amoxicillin can stay in your system for more than 6 hours post-administration, as amoxicillin’s half-life is around 61.3 minutes.


Ampicillin is also an antibiotic used to treat bacterial infections and has been shown to cause a false positive for cocaine in some drug tests. Ampicillin can stay in your system for more than 9 hours post-administration, as its half-life is around 60–90 minutes.


Bupivacaine is also a local anesthetic that causes a false positive for cocaine during drug tests. As the half-life of cocaine is around 2.7 hours in adults, bupivacaine-containing anesthetics can stay in your system up to 16.2 hours or longer post-administration.

Ephedrine nasal inhaler

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


Phenylpropanolamine is a nasal decongestant used for treating 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, phenylpropanolamine-containing drugs can stay in your system up to 20.4 hours post-administration.


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 four 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 four days post-administration, pseudoephedrine-containing drugs can stay in your system.

Other Factors That Affect False-Positive Tests of Cocaine

Importantly, other factors can significantly affect the results of cocaine tests. Those factors differ from one person to another, and include:

  • Your age
  • Your body mass
  • The administered dosage. For example, an overdose of any of the previously mentioned drugs undoubtedly will take longer to be cleared from the body.
  • Whether you’re a light or a chronic user of the drugs.
  • Your metabolic rate for 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 specific timeframe in which to detect certain drugs.

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