Can secondhand weed smoke cause you to fail a drug test? As it stands, the short answer is yes. However, this depends on the test type and your level of exposure to secondhand marijuana smoke.

Might you be at risk of failing a drug test because of your presence among people smoking cannabis? To help you understand the risks, we’ll lay out what the most recent science says.

What Are The Facts?

As a basic rule, if you have recently been near someone smoking marijuana, it is possible that you might fail a workplace or police drug test. There is good news, though.

The chances of testing positive for marijuana after inhaling secondhand smoke are slim. At least, when we are talking about standard urine drug screening.

In 2014, a study published in the Journal of Analytical Toxicology found that non-smokers in close proximity to people smoking marijuana had an altogether negligible risk of testing positive for THC.

  • In the 2014 study, the urine of 12 non-smokers exposed to secondhand marijuana smoke was tested 13-times over a 34-hour period.
  • During the study, only one participant tested positive for THC metabolites. However, this one study participant only tested positive for a brief 4 to 6-hour window after exposure.
  • The 2014 study demonstrated that non-smokers in well-ventilated areas have an even smaller chance of testing positive for THC.

As it stands, these and similar study findings are good news for anyone who might inhale secondhand marijuana smoke before a workplace urine drug test. However, it’s not all plain sailing just yet.

Positive Results Are Still Possible with Different Tests

The most commonly used workplace drug tests in 2020 try to identify marijuana users by looking for metabolites (metabolic by-products) of THC in a test subject’s urine.

Typically, most tests look for 50-nanograms of THC metabolite per milliliter of urine. However, some more sensitive tests can test for as little as 20-nanograms per milliliter.

To make matters even more complicated, some employers don’t use urine drug tests at all. Instead, they use hair follicle and occasionally saliva drug screening.

Can You to Fail a Hair Drug Test From Secondhand Smoke?

Whether you can fail a hair drug test by inhaling secondhand marijuana smoke still rests with your level of exposure to THC. However, evidence suggests that the risk of failure is much higher.

When in an un-ventilated enclosed space, inhaling secondhand cannabis smoke can result in THC being detectable in a person’s bloodstream in as little as 10-minutes. This is important, as this amount of exposure can be enough to see you fail a hair drug test.

  • In 2015, three researchers at the Institute for Forensic Medicine found that hair tests are unreliable when it comes to ascertaining whether people have used, or simply been present around marijuana.
  • 9-tetrahydrocannabinolic acid A (THCA-A), a biological indicator of cannabis use, was found in hair tests from people who had handled, but not used cannabis.
  • The 2015 study went on to show that coming into contact with THC through touch, sweat, and cannabis smoke, was enough to result in hair tests returning as positive for cannabis consumption.

Can You Pass a Hair Test Even After Exposure to Cannabis?

The fact that traces of THC can appear in hair tests among non-cannabis users is worrying.

It is not just employers who use hair tests to identify illicit drug users. Courts and Child Protective Services also use hair tests to decide child-custody cases. The good news, though, is that there ways to lower your risk of testing positive.

How to Pass a Hair Drug Test 

Traces of THC detectable by hair tests occur inside the hair shaft and follicle. For this reason, it is not possible to simply wash traces away with regular shampoo. However, there are specially formulated shampoos on the market that can breakdown THC metabolites in hair.