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You may have thought it was a cannabis urban legend, but there actually is scientific evidence that you could fail a drug test because of secondhand weed smoke.
Don’t panic, but it is actually possible to fail a drug test because of secondhand marijuana smoke, according to the evidence from more than a dozen research papers. That doesn’t mean if you walk through a cloud of marijuana smoke at a concert or stroll through a backyard BBQ that you’ll fail a urine test, but it’s probably a good idea to be wary.
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And considering that smoking is the most common method of consuming cannabis, it’s worth asking: What are the effects of cannabis smoke on those who aren’t actually smoking?
The answer isn’t as clear-cut as one might hope.
How can secondhand marijuana smoke show up in a urine test?
So how does secondhand pot smoke show up in a urine test?
According to a 2017 review of 15 existing research papers, exposure to secondhand cannabis smoke resulted in the presence of cannabinoid metabolites in bodily fluids, specifically in the saliva, blood, and urine. The authors of the review also suggested that higher THC content of the smoked marijuana is correlated with higher the THC metabolite content in the urine.
So yes, is it possible to fail a drug test without smoking — just from secondhand exposure to cannabis smoke.
“Using levels of cannabinoid or THC metabolites found in blood or urine samples to determine marijuana use or intoxication is challenging,” the researchers wrote. “There is no universal threshold that can differentiate between those who have actively smoked marijuana and are intoxicated, those who have actively smoked marijuana in the past and those who have been exposed to second-hand smoke.”
In other words, you could potentially fail a drug test due to secondhand smoke and the technicians performing the test would be unable to tell whether or not your exposure to THC was due to secondhand smoke or actively smoking marijuana.
And secondhand smoke doesn’t necessarily cause only small or trace amounts of exposure. According to the researchers, some of the people who were exposed to secondhand marijuana smoke in some of the research had THC metabolite levels higher than those legally allowed for motor vehicle drivers in a number of jurisdictions.
“This raises questions about whether there should be tolerance for people who claim that their positive urine test result is due to second-hand exposure,” the researchers wrote.
Drug testing, of course, is also impacted by how long THC stays in your system.
The 3 main types of cannabis drug testing include:
- Urine testing
- Hair follicle testing
- Saliva testing
What does a urine test indicate?
Urine tests for marijuana are designed to find tetrahydrocannabinol, or THC, the main intoxicating ingredient in cannabis, as well as the metabolite THC-COOH, which is produced when the body breaks down THC.
A positive result typically entails more than 50 nanograms of THC per milliliter, though this isn’t always the case. In 2019, the National Collegiate Athletics Association (NCAA) increased the THC testing threshold for student athletes from 15 to 35 nanograms per milliliter, from the previous threshold of 5 to 15 nanograms. And in 2020, the National Football League increased the allowed amount of THC in urine tests from 35 to 150 nanograms per milliliter.
How long is THC detectable in urine?
It’s commonly-known that you can fail a urine test for THC even weeks after smoking. This is because THC is fat soluble, which makes cannabis great for infusing oil or butter, but also means that it can stay detectable in your urine for as much as around a month because it is stored in fat cells. And if you’re taking a hair follicle test THC can be detectable for up to 90 days.
But the good news for those who just got exposed to a little secondhand weed smoke? It depends a great deal on how much THC you are exposed to or consume and how often it happens.
According to the Mayo Clinic, THC can be detectable in the urine of chronic users for more than 30 days, while “single exposure to marijuana in nonusers typically can be detected in the urine only up to 72 hours,” the Mayo Clinic states.
In other words, even if you were exposed to a thick cloud of secondhand marijuana smoke, you probably don’t need to worry about a drug test next week.
Hair follicle testing for marijuana
Hair follicle testing involves taking a 100-milligram sample of hair (around 90 to 120 strands) which is removed at the scalp. In addition to THC, hair follicle testing can detect a wide variety of drugs including cocaine, opiates, and amphetamines among others.
The main difference between hair follicle and urine testing is that drugs can be detected in hair follicles for up to 90 days after use and samples are less likely to be adulterated or contaminated during collection.
The good news is that you’re significantly less likely to be given a hair follicle test for a job interview or as a condition of deferred adjudication. The tests also were found to have a high potential for “under-identification of low-frequency use,” according to a 2014 study.
Saliva testing for marijuana
Saliva tests are used to detect the presence of THC, not its metabolites, and are administered by way of a mouth swab. They are much less invasive and easier to administer than urine or hair follicle tests, and can be a popular method of testing in the workplace.
The good news is that for the casual smoker — and potentially even more so for the secondhand smoker — saliva tests can only detect the presence of THC for a few days. Chronic smokers, though, can fail saliva tests for around a month after smoking.
Is exposure to secondhand smoke worse indoors or outdoors?
In a poorly ventilated room, marijuana smoke can linger in the air longer, increasing the level of exposure. This is actually true for any type of smoke. Indoors, the concentration of the chemicals, compounds, and particles in any type of smoke is higher, and it doesn’t clear out nearly as quickly as it does outdoors.
The bottom line, if you’re in an environment where people are smoking, you’ll be less exposed for less time if you’re outside.
Can you get high from secondhand smoke?
The “contact high” is a staple of cannabis lore. It typically entails someone who finds themself in a room where joints are being passed at a rapid clip, and feels a secondhand high even though they didn’t partake.
While in some cases this may be something of a placebo effect, there is some scientific evidence to back up the cannabis urban legend of a contact high.
In the 2017 review, researchers found that the psychoactive effects they observed were also present in those exposed to secondhand cannabis smoke, although weaker than for those actually smoking it. The researchers also stated that there was a correlation between the intoxicating effects of THC from secondhand exposure and the strength of the cannabis strain involved.
However, the researchers stressed that many of the scenarios that were observed took place in closed areas with limited ventilation and they probably don’t apply as much to more common scenarios like smoking outside.
Is secondhand cannabis smoke or vapor dangerous?
A 2019 study published in Preventive Medicine Reports was the first of its kind to examine the effect of indoor secondhand cannabis smoke on child health. Researchers placed air particle monitors in 298 family homes across San Diego County, CA and examined how particulate material data impacted children’s health.
The study found an association between indoor cannabis smoking and adverse health outcomes in children, including ear infections, asthma, other respiratory dysfunction, and skin conditions, but the association was not statistically significant.
The research also suggests that the act of combustion and smoke produced, rather than what material is being smoked, poses the greatest health threat.
Very little research on the topic has been done, however.
Vaporizing, on the other hand, does not involve combustion. So is it safer?
Non-combustible forms of cannabis “may be associated with lower relative harm both for users and for those who are exposed to the aerosol vapor” compared to those exposed to secondhand tobacco smoke, wrote the authors of a 2018 study published in the International Journal of Environmental Research and Public Health.
“While there is currently less evidence on the health effects of exposure to secondhand cannabis smoke, cannabis smoke is similar in chemical composition to tobacco smoke (although in varying concentrations),” they wrote.
There are currently no scientific studies on the long-term health effects of exposure to secondhand cannabis smoke, vapor, or other products. With more cannabis products on the market, that gap needs to be filled in order to properly assess and address the public health concerns involved.
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