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Updated on September 26, 2022

Can You Fail a Drug Test From Secondhand Smoke?

It is possible, although unlikely, to fail a drug test from secondhand smoke. It depends on how much secondhand smoke you were exposed to and how ventilated the space was.

Drug tests have a cut-off level. This is the maximum concentration of THC the test allows in a sample. 

You'll fail the test if your sample’s concentration exceeds the maximum concentration. People exposed to secondhand smoke rarely reach this level, but it can happen.

But this trace amount of THC doesn’t remain in the system long. 

Unless you spend time in a hotbox before the test, you’ll likely pass a drug test even if you were recently exposed to secondhand smoke. 

Can You Get ‘High’ From Secondhand Marijuana Smoke?

Yes. However, the ‘high’ you get from secondhand smoke isn't the same as that produced from physically ingesting marijuana.

Every time someone smokes a substance (e.g., tobacco or marijuana), the exhaled smoke contains traces of the active ingredients. 

In the case of marijuana, secondhand smoke contains residual THC, CBD, and other cannabinoids. 

If exposed to secondhand marijuana smoke, THC (marijuana’s active ingredient) may be found in your blood. However, the amount of THC is much less than it would be if you smoked or ingested marijuana yourself. The levels also won’t trigger a failed drug test. 

Secondhand marijuana smoke contains residual amounts of THC. The lungs won’t absorb the THC—but you can still get high.

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Current Research About Secondhand Smoke & Drug Tests

Several studies confirm the circumstances under which secondhand smoke produces trace amounts of THC in a drug test.

Effects of Secondhand Smoke in Ventilated and Unventilated Rooms

According to a 2015 study from Johns Hopkins University, smokers and non-smokers were paired together in both ventilated and “hotbox” spaces.2 

The smokers were told to smoke 10 joints each for an hour. Following the hour, each group was drug tested using blood and urine samples.2

The non-smokers in the ventilated room felt no intoxicating effects and tested negative for THC. The non-smokers in the unventilated room felt intoxicated and tested positive for trace amounts of THC.2

Effects of Passive Exposure to Secondhand Smoke

This study showed that secondhand exposure to marijuana could show up on a drug test.1 

The study's goal was to understand the health effects that passive exposure had on non-smokers. The study reviewed 15 existing experimental studies to determine if THC could be detected in bodily fluids after exposure to secondhand smoke.1 

They found detectable levels of THC in the blood and urine of non-smokers. They also found that those exposed to secondhand smoke reported feeling the drug's psychoactive effects. 

However, the level of intoxication was weaker for non-smokers than for smokers.1

Cardiovascular Effects of Secondhand Smoke

Another study on lab rats showed that just a minute of exposure to marijuana substantially impairs endothelial function in the test subjects for at least 90 minutes. The endothelium is a thin membrane that lines the inside of the blood vessels and heart.

The study concluded that exposure could cause a similar adverse cardiovascular effect on people exposed to smoke (regardless of whether it came from tobacco or marijuana).3

Effects of Extreme Secondhand Exposure on Urine Test

Finally, a systematic study published in the Journal of Analytical Toxicology showed that extreme exposure to secondhand smoke could produce a positive urine test. These positive tests are rare and “occur only under environmental circumstances where exposure is obvious.”4

Hotboxing & Secondhand Marijuana ‘High’

Some marijuana users practice ‘hotboxing’ to enhance the effects. A hotbox is when people gather in a small room (sometimes a vehicle) with closed doors and windows.

This produces a stronger high than smoking alone because every inhalation contains marijuana smoke. It's possible to get high from secondhand cannabis smoke using this method, but it's not easy.

You need to inhale a significant amount of secondhand smoke to achieve your desired —or undesired— result.  In most cases, simply being in a room with someone isn’t going to produce a significant contact high.

Secondhand marijuana smoke does not significantly raise THC levels in the body. But there are still concerns about the health and safety of passive smoking. If you aren’t a regular marijuana user, you’re likely to have a more intense experience from a contact high.

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How Long Does THC Stay in Your System?

The length of time THC remains in your system depends on how much you smoke and/or how much you were exposed to. 

THC’s metabolites remain in your body for much longer than the duration of effects. This means a drug test could still detect recent marijuana use long after the high wears off.  

In some cases, evidence of the drug can be detected for weeks or months after the last use. 

The type of drug test also determines how long a drug can trigger a positive result. For example:

Blood Test

The body rapidly metabolizes THC, which means it will only remain detectable in the blood for a few hours or up to two days after a single use.

For heavy marijuana users, blood tests detect THC in the bloodstream for as long as one week.

Saliva Test 

THC appears in saliva about an hour after use and remains detectable for approximately one to two days. 

What you eat, how much you drink, brushing your teeth, or using mouthwash might speed the removal of THC from saliva. This is why these types of tests are considered unreliable for marijuana testing.

Urine Test

This is the most common type of drug test for marijuana. THC is detectable for a longer period in urine (several weeks after use). The time it’s detectable in urine depends on how often you use the drug. 

Additionally, frequency of use plays a role. Frequent/daily users can test positive for up to 65 days after the last use.

Hair Test

THC metabolites remain in the hair for longer than any other system in the body. 

On average, evidence remains is present in your hair for about three months. People with longer hair test positive for THC longer than those with short hair.

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  1. Holitzki, Hannah, et al. “Health Effects of Exposure to Second- and Third-Hand Marijuana Smoke: A Systematic Review.” CMAJ Open, 2017.
  2. Hopkins Medicine “Secondhand Marijuana Smoke Can Cause Range of Detectable Effects, Study Finds.” The Hub, 2015.
  3. Wang, Xiaoyin, et al. “One Minute of Marijuana Secondhand Smoke Exposure Substantially Impairs Vascular Endothelial Function.” Journal of the American Heart Association, 2016.
  4. Cone, Edward J., et al. “Non-Smoker Exposure to Secondhand Cannabis Smoke. I. Urine Screening and Confirmation Results.” Journal of Analytical Toxicology, 2014.
  5. “Secondhand Smoke and Cancer.” National Cancer Institute, 2009.
  6. National Institute on Drug Abuse. “What Are the Effects of Secondhand Exposure to Marijuana Smoke?”, 2018.

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