Medically Reviewed by
Jason Crawford

Article Last Updated on December 29, 2022

Drug testing has become a common prerequisite when you’re applying for a job in certain sectors, and it’s also a frequent practice in the workplace. Employers require drug tests (also called immunoassays) as a measure of precaution because they want to make sure that their employees are not taking any illicit drugs that might impair their performance.

The most commonly used tests for drug screening in the workplace are urine tests because they are noninvasive, reliable, fast, and affordable enough to cover a larger number of individuals in a company.

If you’re a cannabis user, given enough time, you can abstain from cannabis use and detox before your test to avoid failing it. However, many non-cannabis users are often worried about false positives. This can happen due to a number of things – either consuming CBD oil, inhaling secondhand smoke from your friends who smoke weed, or taking prescription drugs.

What Do Urine Drug Screens Typically Look For?

Urine drug tests are designed to detect different categories of illicit drugs, such as amphetamines or methamphetamine, cocaine, opiates (heroin), phencyclidine (PCP), as well as marijuana.

Depending on the situation, other drug categories may be included, like barbiturates, designer drugs (bath salts, ecstasy), benzodiazepines (Valium, Xanax), or prescription opioids (methadone, oxycodone).

Even though marijuana use is either legal or decriminalized in most states in the US, it’s still included in standard drug tests as marijuana is still illegal under federal law.

How Do Drug Tests Detect Weed?

When it comes to detecting marijuana, drug tests are made to be sensitive to THC (tetrahydrocannabinol) byproducts, also called metabolites, which are created when your body starts breaking down THC. These metabolites bind to the fat cells and remain much longer in your body than THC until they get fully eliminated, little by little.

How long the THC metabolites will stay in your body depends on your weed habits, such as frequency of use and the potency of the strain you use. Generally, THC can remain detectable in your urine sample from about five days at least, to 4 weeks at most.

However, it’s important to note that drug tests have specific cutoff levels for a drug to be detectable. The cutoff level is the threshold at which the concentration of a drug can be detected. So what is a high THC level in urine? Anything at or above this level will be detected. For urine drug testing, the cutoff level for THC is at 50 ng/ml (nanograms per milliliter). Cannabis users will typically try to get their THC concentration below cutoff levels beforehand to avoid failing the test.

What Can Cause a False Positive Drug Test?

In most cases of a positive drug test result, the urine sample is retested (confirmatory testing) using the gas chromatography-mass spectrometry (GC-MS) method. This is a more complicated method, but it provides a very reliable way for the lab to check if the result was falsely positive or not. However, this method can also produce false negatives if the test is not optimized to identify all potential substances in the sample.

False-positive results are not impossible, especially when you take other medications. Some drug classes that have produced false positives include antihistamines, antidepressants, some over-the-counter drugs (OTC), antipsychotics, decongestants, and analgesics.

Medications That Can Cause a False Positive Result for THC

There are some medications that can show up on a drug test as THC and cause a false positive.


It has been suggested that common over-the-counter anti-inflammatory medications like ibuprofen (Advil) and naproxen (Aleve) could cause a false positive drug test for THC. Additionally, Tramadol, another commonly used pain medication, could make you test positive for PCP.

Efavirenz (Sustiva)

Efavirenz (Sustiva) has been observed to result in false-positive test results for THC and sometimes for benzodiazepines.

Proton Pump Inhibitors

Proton pump inhibitors or medications used to treat GERD (gastroesophageal reflux disease) or PUD (peptic ulcer disease) can cause you to test positive for THC. Prilosec (omeprazole), Nexium (esomeprazole), and Prevacid (lansoprazole) are the most commonly used medications for GERD and PUD.

Can CBD Cause False Positive Results?

One of the most common questions regarding cannabis and urine drug screening is whether CBD (cannabidiol) can cause false-positive test results. Truth is, false positives due to CBD is not unheard of, however, pure CBD shouldn’t make you fail the test.

Since drug tests don’t look for the metabolites of all cannabinoids present in weed, but just THC, if you use pure CBD oil, for example, it will not be detected. However, full-spectrum CBD oil has trace amounts of THC. 

Normally, there should be no more than 0.3% of THC in the CBD oil, but some manufacturers may have false information on the label regarding the THC content. This would mean that you’d be ingesting more THC than you want, which can show up on a drug test. Legitimate manufacturers test their products in third-party labs and often have the results up on their websites.

Can Passive Inhalation of Marijuana Smoke Make You Fail a Urine Test?

Another common question about drug screening is whether non-users can fail a drug test if they’re often around people who smoke weed.

Passive inhalation of marijuana smoke is unlikely to make you fail a drug test, especially if you’re out in the open. When it comes to second-hand marijuana smoke, studies have shown that ventilation is the key to avoiding getting a “contact high.” As long as there is proper ventilation and you’re not so enveloped in smoke that you can barely see, it’s very unlikely to fail a drug test due to secondhand weed smoke.

Medications that Can Cause a False Positive Result for Other Drugs

Some medications can cause a false-positive test result for other drugs.

Cough Suppressants

Cough suppressants that contain the active ingredient dextromethorphan, such as Tussin and Delsym, may cause the drug test to show up as positive for PCP or opiates.


Decongestants like Sudafed can make you fail a drug test because they contain pseudoephedrine, which is also a key ingredient in methamphetamine.


Common ADHD medications Ritalin and Adderall which contain the active ingredient methylphenidate can easily result in a false positive test for amphetamines and methamphetamines.

Quinolone Antibiotics

Quinolone antibiotics like Levaquin (levofloxacin) and Cipro (ciprofloxacin), as well as Rifampin, can result in a false positive drug test for opiates.


Antihistamines that contain diphenhydramine (Benadryl) and doxylamine (Unisom) can cause false positives for PCP, methadone, or opiates.


Phentermine is a very commonly prescribed weight-loss medication in the US, but it can cause a false positive drug test result for amphetamines.


Some antidepressant medications like Zoloft (sertraline), Prozac (fluoxetine), Seroquel (quetiapine), Effexor (venlafaxine), Wellbutrin (bupropion), trazodone, and amitriptyline can result in a false positive for amphetamines or LSD.

Other Substances That Can Cause a False Positive Drug Test Result

There are two commonly consumed substances that are known to cause false positive drug tests.

Tonic Water

Tonic water contains quinine, which can make you test positive for opiates. However, only ingestion in larger quantities will make quinine detectable on a drug test.

Poppy Seeds

Poppy seeds are long known to be able to cause a false positive test because they contain morphine and codeine. However, you’d have to ingest a lot of poppy seed bagels to cause a false positive.

Bottom Line – A Confirmatory Test May Be a Good Option if You Get False Positive Test Results

​False-positive results on a drug test are rare, but they can happen, especially with the rate of frequency of drug testing in the workplace today.

Getting false-positive results can be disconcerting, but if you haven’t been consuming weed or any other kind of drug, getting a confirmatory test will save you a lot of trouble.

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.