Can You Fail a Drug Test From Secondhand Weed Smoke?

contact high smoke
By Andrew Ward Updated July 12th

Fact-checked by Deb Tharp

Weed legalization has led to an uptick in adult consumption. At home and in public, people are more likely to be exposed to cannabis smoke. This can raise concern for some people, particularly those who may have to take a drug test for one reason or another.

Can secondhand smoke make you fail a drug test? Read on to find out the answer to that question and others about weed smoke, cannabinoids and more. 

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Can You Fail a Drug Test from Secondhand Smoke?

Most research and anecdotal feedback suggest that you are unlikely to fail a drug test from secondhand cannabis smoke. Still, the outcome doesn’t appear to be entirely off the table.

A 2014 study of eight cannabis users over three sessions found that the chances of failing a test from secondhand smoke hinged heavily on the plant's potency and the sensitivity of the screening.¹ 

Researchers saw that the subject pool of three women and five men received “sufficient amounts of THC” when exposed to short-term, high-intensity smoke. They also noted that the sensitivity of the screening would play a significant factor in the outcome. 

Overall, the analysis found that “extreme smoke exposure” could result in a positive test when using screenings with lower cut-off concentrations. Most exposure won't get picked up on cannabis screenings set to the standard 50ng/ml sensitivity. Your risk of a positive test will increase if the analysis is set to 20ng/ml.

Ventilation played a significant factor as well. Without proper air filtration, the chances of failing a screening can increase. But, to reach these levels of exposure, researchers filled the room with so much pot smoke that some subjects wore protective goggles to avoid eye irritation. Since most of us won’t hotbox a room to that degree, secondhand cannabis smoke should not trigger a positive test. Still, there are cases where lower-intensity tests could produce a positive result.

The following year, analysis from Johns Hopkins University reached a similar conclusion on ventilation and positive screenings for secondhand smoke. Like the research from the year before, the May 2015 study noted that secondhand exposure had to be at "extreme" conditions to come up on a test. The research also confirmed that secondhand smoke in a low or non-ventilated room could cause mild intoxication. Many know this as a "contact high." 

We also have to consider the reliability of drug screenings themselves. Misinterpretations of results can happen. If a clinician makes a mistake or if a false positive or false negative occurs, the screening subject faces potentially steep consequences. Punishments include incarceration, job termination, and the loss of housing or parental rights. 

And let’s not forget your health. Your odds of failing a drug test due to secondhand cannabis smoke are low. Still, exposure to smoke, in general, comes with health risks. Secondhand cannabis smoke may lead to adverse short- and long-term effects, including:

  • Asthma attacks 
  • Lung irritation 
  • Respiratory discomfort or infection

How Long Will Secondhand Weed Smoke Last in My System?

secondhand weed smoke

There is quite a difference between how long cannabis remains in your system when consuming or receiving it secondhand. According to most anecdotal feedback and some lab analysis, THC and other cannabinoids can stay in your system for anywhere from 30 to 90 days. That time frame will be largely determined by the amount consumed in recent days, weeks, and months. Other factors, including body composition and the potency of the cannabis, seem to come into play. 

Secondhand weed smoke remains in your system for a significantly shorter period. Depending on your source, secondhand cannabis smoke should be out of your system in about three days. Some diagnostics suggest that it could be gone within 24 hours.

So, while you are unlikely to test positive due to secondhand pot exposure, use caution if a screening is coming up. You don't want to get in trouble because you hung around in a hot box for too long. Still, remember that you would need to be around uncommon levels of cannabis smoke to get there. But it’s still always a good idea to use caution if you have a test coming up.

The type of drug screening will also come into play. Blood, saliva, and urine tests are considered the most effective and accurate methods. However, hair tests can detect cannabis use dating back several months. Blood, saliva, and urine analysis typically only go back to 30 or so days. 

What About Secondhand CBD Smoke?

Secondhand CBD Smoke

There isn't much difference between secondhand CBD and THC smoke regarding cannabis drug screenings. In fact, there isn't much of a difference between any cannabinoids when it comes to secondhand smoke. However, there is a reasonable degree of difference when it comes to most drug screenings. 

With CBD being federally legal, screenings rarely, if ever, test for it.. That certainly isn't the case with THC. THC-COOH, the metabolite byproduct created by the body metabolizing THC, is of primary interest during cannabis drug tests.  

The focus on THC and the legality of CBD mean that the latter is unlikely to trigger a positive test during a drug screening. However, keep in mind that not all CBD is free of THC. Federally-legal hemp products are allowed by law to contain up to 0.3% THC. When consumed in large enough doses, it may trigger a positive test. This outcome is much more likely when you’re using the CBD product yourself over a long period of time than if you were exposed to secondhand smoke.. If you’re looking to keep using CBD while avoiding THC for a drug test, it’s best to stick to CBD isolates with a 0% concentration of THC.  Still, even though eating or inhaling enough THC from federally-legal CBD products to register on a drug test is highly unlikely, there’s no proof that it’s impossible either.

It's always best to use caution with a drug screening coming up. Even if the chances are low, you may want to hold off on consuming CBD in the lead-up to your test. Or, at the very least, keep your dosage low.

What to Do If You Are Exposed to Secondhand Cannabis Smoke

Secondhand Cannabis Smoke

Avoiding secondhand smoke can be more complicated than it seems. It won’t be hard to smell or spot the stuff, but, at times, it can be challenging to pass up the events attached to it. Still, if you want to avoid secondhand smoke, consider steering clear of places like:

  • Cannabis consumption lounges
  • Buildings and venues that allow smoking (Certain restaurants, concert venues, clubs, etc.)
  • Smoking sections of bars, restaurants, venues, etc.

You may also want to avoid outdoor locations where cannabis is allowed. In some states, like New York, public weed consumption is legal. Though, with outdoor air, you should have ample ventilation to avoid secondhand smoke. Still, you may want to use caution. 

You can’t do much to reverse any effects caused by secondhand smoke. Your best bet is to react once you feel something is off. Move away from the oppressive smoke and/or smell. Find a place where your eyes, sinuses, and throat aren't bothered. 

Avoiding cannabis smoke isn’t the most challenging task in the world. Still, it can be hard to pass up on places, people, and events that may bring you into contact with it. The chances are slim, but you could find yourself failing a drug screening due to secondhand cannabis smoke or CBD consumption. If you have a drug screening coming up, use caution in the days and weeks leading up to it.


¹ Cone, Edward J., George E. Bigelow, Evan S. Herrmann, John M. Mitchell, Charles LoDico, Ronald Flegel, and Ryan Vandrey. 2014. “Non-Smoker Exposure to Secondhand Cannabis Smoke. I. Urine Screening and Confirmation Results.” Journal of Analytical Toxicology 39 (1): 1–12.

The information in this article and any included images or charts are for educational purposes only. This information is neither a substitute for, nor does it replace, professional legal advice or medical advice, diagnosis, or treatment. If you have any concerns or questions about laws, regulations, or your health, you should always consult with an attorney, physician or other licensed professional.

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