Medically Reviewed by
Jason Crawford

Article Last Updated on January 15, 2023

Drug screening is common in a lot of companies all over the world, but especially in the US. The most common ones are the urine drug screens which test your urine sample for the presence of drugs and drug metabolites. These tests can sometimes be the reason for not getting hired for a certain position which is why getting a false positive on your mandatory workplace drug test isn’t a scenario people look forward to. 

While this can sometimes be a result of the ingestion of commercially available hemp seed products and cannabis products that contain more THC than the label implies, other times it’s a result of some medication and other substances that can cause a positive drug test. In this article, we’ll go over the reasons why you can get a positive drug test, as well as give you some of the most common causes for getting a false positive.  

What Is a False Positive Drug Test?

A false positive drug test result occurs when some of the molecules in your body are recognized as illegal drugs by the analytical drug detection method when, in fact, you haven’t ingested any drugs. Drugs that are commonly screened for include:

  • Amphetamines/methamphetamines;
  • Benzodiazepines;
  • Barbiturates;
  • Cocaine;
  • Marijuana;
  • Methadone;
  • Opioids;
  • Phencyclidine (PCP).

Generally, drug tests can show false positives in about 5% to 10% of cases, and 10% to 15% percent may yield false negatives. Remember that a positive drug test can affect whether or not you get the job, promotion, or education that you desire, which is why minimizing the chances of getting a positive drug test is imperative. Apart from consuming drugs, several over-the-counter medications, common prescriptions, as well as some herbs, vitamins, and foods can also trigger a false positive on your drug test, and in this article, we’ll discuss them specifically.

What Tests Are Used to Check For THC Presence?

UDS is the immunoassay test that uses antibodies to detect the presence of specific drugs or metabolites and it is the most commonly used method for drug screening. The advantage of this test is that it has rapid detection, the downside being that it can cause false-positive results. If a person does get a positive test result, often a more specific gas chromatography-mass spectrometry (GC-MS) confirmatory test is done which has a threshold of 15 ng/mL and it either confirms or denies the previous test.

Medications That Can Cause False Positive Drug Tests for THC and Other Drugs

Below we’ll give you a list of the common over-the-counter medications and prescription drugs that may give you a positive drug test.

Analgesics/ NSAIDS

Consuming some analgesics could trigger a false positive result on your next drug test. Tramadol, which is often used as pain medication, may result in a false positive test for PCP. Some over-the-counter anti-inflammatory pain medications, such as Advil (ibuprofen) and Aleve (naproxen), may result in you getting a false positive for THC (tetrahydrocannabinol), barbiturates, or PCP. Finally, the medication commonly prescribed for arthritis, Daypro (oxaprozin), may result in a false positive for benzodiazepines. 


Antibiotics like Levaquin (levofloxacin) or Cipro (ciprofloxacin), known as quinolone antibiotics, which are commonly prescribed for certain infections, may trigger a false positive urine result for opiates. Also, a common antibiotic used for tuberculosis, called Rifampin, can lead to you getting a false positive test for opiates.


Some common antidepressants can cause a false positive for LSD, amphetamines, or benzodiazepines and those include:

  • Amitriptyline (Amitril);
  • Effexor (Venlafaxine);
  • Sertraline (Zoloft);
  • Prozac (Fluoxetine);
  • Seroquel (Quetiapine);
  • Trazodone;
  • Wellbutrin (Bupropion).


Antihistamines and some sleep aids like Benadryl which contain diphenhydramine, are another group of medications that can also trigger a positive drug test result for methadone or phencyclidine (PCP). Doxylamine, on the other hand, which is an active ingredient in Unisom, can cause a false positive for PCP.

Central Nervous System (CNS) Stimulants

Some of the most commonly used medications to treat ADHD, such as Ritalin (methylphenidate) and Adderall, may cause a false positive for amphetamines and methamphetamines.

Cough Suppressant

Commonly used cough suppressants, such as Robitussin and Delsym, that have the active ingredient dextromethorphan, may result in a positive drug test for phencyclidine (PCP) or opiates.


You can also get a positive drug test for methamphetamines if you’ve consumed a decongestant called Sudafed (pseudoephedrine) which contains an ingredient that is also used to make amphetamines.

HIV Medication

A less sensitive drug screen can show a positive result for THC if you’ve consumed Efavirenz (Sustiva), a drug that helps treat HIV infection. If this happens, it can be useful to get tested once more with a more sensitive test that can distinguish between the two compounds, although it’s also useful to tell the lab that you’re taking HIV medication so they can take it into consideration.

Proton Pump Inhibitors

Commonly used proton pump inhibitors, such as Nexium (esomeprazole), Prilosec (omeprazole), and Prevacid (lansoprazole), which are used to treat peptic ulcer disease or gastroesophageal reflux disease can cause a positive test for THC.

Common Substances That Can Cause False Positives

Apart from prescription medication, there are other substances that can lead to a false positive drug test.

Vitamin B Supplements

There are cases when the B2 vitamin, also known as riboflavin, which is found in hemp seed oil may cause a false THC reading.

CBD (Cannabidiol)

The non-psychoactive cannabinoid cannabidiol has become very popular due to its pain-relieving, sleep-promoting, and anxiety-relieving properties. In the US, CBD products that contain less than 0.3 THC are legal to use. However, not all CBD products are regularly tested by third-party laboratories to determine their THC content, so there are cases when a product contains more THC than what’s listed on the label. So, if you end up consuming a CBD product that has a higher amount of THC than that indicated on the label, you may get a positive drug test result.

Hemp Foods

Apart from NSAIDs, efavirenz, and dronabinol, hemp food consumption may also cause false-positive tests for THC. Remember to always check the label of your hemp food products to see whether they’ve been tested by third-party laboratories.

Poppy Seeds

Poppy seeds are another substance that may affect your drug test results because they can contain morphine and codeine. If you ate a bagel or a muffin sprinkled with poppy seeds before your mandatory drug test, you may get a positive test result for opioids. Since poppy seeds are derived from the seedpod of the opium poppy, they may contain some trace amounts of opium. Depending on the federal government threshold for opiates, you may get a positive drug test because of it if the drug testing laboratory has a lower threshold level.

Tonic Water

Another common drink that can lead to a false-positive result for opiates is tonic water. Because tonic water contains quinine, when you consume it in large amounts prior to your drug test, you may end up with a positive one.

Useful Tips Before You Go In for Your Mandatory Drug Screen

If you believe that you’ve consumed some of these over-the-counter medications or a prescription drug that can affect the results of your test, it’s a good idea to be honest with the tester before even taking the test. It’s also useful to have the prescription on hand so you can also show it on the day of the test. However, if it’s an over-the-counter product, remember to take a doctor’s note with you so you have some documentation for the drug you’ve taken. So the administrator may even schedule another test 30 to 60 days later, which is plenty of time for you to get a negative test result on the next one.

Another good idea is to avoid consuming some of the foods and drinks that we’ve mentioned in this article, such as vitamin B supplements, CBD, hemp foods, poppy seeds, or tonic water in the days leading up to your test. Once you’re done with your test, you can consume these foods as much as you desire. And remember, cheating on your upcoming drug test is never a good option as you can get caught and even lose your job. However, we have some tips in this article that can help you eliminate the cannabis metabolites from your body faster. We wish you all the best on your upcoming drug test!

A passionate advocate for the benefits of cannabis. Fraser Horton, who has a background in botany and a strong love of nature, has spent years researching how cannabis affects the body and mind. He established Leaf Nation in 2020, where he has devoted himself to educating people about the legalisation of marijuana and its safe and responsible use. Fraser is committed to highlighting cannabis’ potential for improving wellness and working to dispel the stigma associated with its use.


The information presented on this page is provided as a public service to aid in education and is derived from sources believed to be reliable. Readers are responsible for making their own assessment of the topics discussed here. In no event shall Leaf Nation be held reliable for any injury, loss or damage that could happen if using or abusing drugs.