What Can Cause a False Positive for THC

THC is an abbreviation of Tetrahydrocannabinol, which is the major constituent of cannabis. Cannabis is commonly known as marijuana, Ganja, grass, Hashish, Hemp, Indian hemp, Pot, reefer, weed.

THC administration alters the state of consciousness, affects the perception of time, place and mood, and causes euphoria. That’s why THC is amongst a group of highly addictive drugs that drug tests crucially test for.

What Can Cause a False Positive for THC

  • Hemp oil-containing supplements
  • Pantoprazole
  • Ibuprofen
  • Naproxen
  • Dronabinol
  • Efavirenz
  • Ketoprofen
  • Piroxicam
  • Promethazine
  • Sulindac
  • Tolmetin

Why Those Drugs Cause A False Positive

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

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 for THC. So, if you’re currently administering/or if you have administered any of those drugs, the proper question should be: how long can those drugs stay in the system?

Hemp oil

Hemp oil is commonly consumed within nutritional supplements. Hemp oil-containing products are likely to cause a false positive for THC, as hemp oil is already extracted from plants having origins that are relatively similar to this of THC.

Pantoprazole-containing drugs

Pantoprazole is a drug used to decrease the levels of stomach acids. Thus it is used to treat Zollinger-Ellison syndrome and other issues related to the high level of stomach acids. Pantoprazole belongs to a group of drugs known as proton pump inhibitors (PPIs). Protonix is a common example of pantoprazole-containing brands.

Research shows that the half-life of pantoprazole is around 1 hour. Therefore, up to 6 hours post-administration or longer, pantoprazole-containing drugs can stay in your system. Regarding THC, not only pantoprazole; but also other proton pump inhibitors are likely to cause a false positive for THC.


Ibuprofen is an analgesic, antipyretic and anti-inflammatory drug from a family of drugs known as NSAIDs, which means that Ibuprofen is not derived from steroids. Ibuprofen is contained in many brands and strengths that are over the counter (OTC) and also prescribed. For example, Genpril, Motrin IB, Advil, Midol IB, and Proprinal. Ibuprofen can stay in your system for up to 24 hours, since the last dose. Research shows that 28 hours post-administration of ibuprofen, the test couldn’t detect ibuprofen in urine.


Naproxen is also an analgesic belonging to the same group of drugs known as nonsteroidal anti-inflammatory drugs (NSAIDs). Aleve, EC-Naprosyn, Flanax, and Midol are examples of the common brands containing naproxen.

Naproxen has a half-life of 15 hours. Therefore, up to more than 3.75 days, postadministration, naproxen-containing drugs can stay in your system.


Sulindac drug used to treat chronic arthritis, and it also belongs to NSAIDs. Sulindac has a half-life of 7.8 hours; while its metabolite has a half-life of 16.4 hours, which means that up to 1.95 and 4.1 days post-administration, Sulindac can stay in your system.


Tolmetin is also a non-steroidal anti-inflammatory drug used to treat arthritis. Tolmetin is eliminated from the body, depending on two elimination rates. Thus, it is expected that Tolmetin stays in your system for up to 24 hours post-administration.


Dronabinol is a synthetic drug similar to cannabis. That’s why it is commonly called marijuana. Marinol and Syndros are examples of common drugs containing Dronabinol. Because of the long half-life of naproxen that ranges from 25 to 36 hours, up to 9 days post-administration, Dronabinol-containing drugs can stay in your system.


Efavirenz is a drug used to treat HIV infection (AIDS). Sustiva is an example of the common brands containing Efavirenz. The half-life of Efavirenz ranges from 40 to 55 hours. Thus, up to 13.75 days post-administration, Efavirenz -containing drugs can stay in your system.


Ketoprofen is an analgesic used to treat menstrual pain and arthritis. Orudis is an example of Ketoprofen-containing brands. The half-life of Ketoprofen ranges from 1.1 to 4 hours, and it increases to 5.4 hours, in case of administering a certain dosage form of Ketoprofen known as an extended release form. Therefore, up to 16 and 32.4 hours, respectively, Ketoprofen-containing drugs are likely to stay in your system.


Piroxicam is an ingredient used to treat arthritis. Feldene is an example of Piroxicamcontaining drugs. Piroxicam has a half-life ranging from 30 to 86 hours, resulting in prolonging the time Peroxicam-containing drugs can stay in your system for up to 21.5 days 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 4 days post-administration, promethazine-containing drugs can stay in your system.

Other factors

Importantly, other factors can significantly affect the results of THC 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.
  • 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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