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Can Second-hand Marijuana Smoke Show up on a Drug Test?

Awareness on the effects of marijuana has often been convoluted in the past, being the subject of many myths and misconceptions.

These myths get tossed around among scientifically literate groups and “dude/bro” college fraternities alike – a crowd favourite being that second-hand marijuana smoke can be detected in a drug test.

What Research Has Concluded so Far

Many people are quick to assume that simply by hanging around pot-smokers or places where marijuana smoke can be easily inhaled, leads to a failed drug test.

Well, in a way, this is justified because, for one, weed has gotten ever more potent over the years.

One way to detect marijuana is through urine tests, which looks for the active metabolite or ingredient in marijuana, THC, to determine if the subject has been exposed to the drug either actively or passively. The fact that this chemical is directly responsible for many of marijuana’s psychoactive properties doesn’t help, especially given that most strains of the drug in recent years have been deliberately bred to contain higher amounts of THC.

One study, conducted by the University of Calgary in 2017 revealed that THC was detectable in the body after just 15 minutes of exposure to passive marijuana smoke. The study concluded that anyone exposed to the smoke in a poorly ventilated environment with windows sealed tight would test positive after just 15 minutes of exposure.

Furthermore, it was revealed that it could take up to 48 hours for the active metabolite in marijuana, THC, to clear up from the subject’s system.

However, another study spearheaded by researchers at the John Hopkins University School of Medicine, which was published in the Journal of Analytical Toxicology three years earlier, concluded results that would have non-smokers with weed-smoking friends believe that they have little to worry about.

After pairing up several pot smokers and non-smokers in a sealed compartment for an hour, scientists discovered that subjects’ urine samples easily surpassed detectable levels of THC, i.e. 50 nanogram per millilitre (ng/mL) – this was 4-6 hours after the test had transpired.

They took it a step further by using a more advanced test which is typically not available at offices, in order to detect THC levels below the 50 nanogram per millilitre threshold. After 24 hours, THC concentrations dipped even further below the detectable level.

Researchers were quick to point out that failed drug tests due to second-hand marijuana smoke is rare because results typically turn up positive in the hours immediately following exposure, especially if subjects have been exposed to the smoke in more concentrated environments – a bathroom or closed kitchen with poor ventilation or a small room with inadequate airflow and again, very little to no ventilation.

To prove their point, researchers ventilated the smoke test site, making the marijuana fumes less concentrated. Urine levels of test subjects showed even lower levels of THC – in fact they did not even come close to the 50 nanogram per millilitre detectable threshold.

From this, we can deduce that the chances of failing a drug test are somewhat high, only if you were to inhale second-hand pot smoke in an enclosed environment with fairly poor ventilation – and then asked to take a drug test a few hours later.

So, just to be safe, why risk it? If you feel that you may fail a drug test, then you need to change the crowd you hang out with or if you can’t avoid it, just see to it that you’re not inhaling any second-hand pot smoke 24 hours prior to the test.

But is it really all that simple? Let’s look at a few more findings, shall we?

Is There Too Much THC in Your System?

A 2010 study observed cannabis concentrations in blood and urine samples of test subjects after they inhaled second-hand pot smoke in an Amsterdam coffee shop for three straight hours. Results revealed an interesting conclusion: even though subjects absorbed the main psychoactive compound, THC, it was absorbed in trace quantities – certainly not enough to get them high.

Furthermore, in the blood sample, traces of THC could be found, but only for about 6 hours immediately following exposure.

A research paper from six years earlier shared similar results – concluding that fluid tests for passive marijuana inhalation can only return positive if subjects are tested within 30 minutes of exposure.

A 2015 study declared that non-consumers of pot actually need to be “hot boxed” in a room with virtually no ventilation for a good 60 minutes before they will test positive for THC metabolites; that is, if the test is taken no later than 24 hours after exposure.

Let’s piece up the facts here: the only real way you are failing that drug test is if you take in a fairly large quantity of second-hand cannabis smoke, and even then, in the moments leading up to the drug test. So in short, it would be quite the challenge to inhale massive quantities of passive pot smoke which could register a failed drug test.

However, all this is in the context of blood and urine tests. Even though hair DNA tests are rare, some employers may have taken the liberty to incorporate those. Hair testing can actually detect traces of second-hand pot smoke easily.

If you are concerned about failing an upcoming drug test, then play it safe: stay away from pot-smoking crowds entirely or stay clear of all such environments for at least 24 hours.

Have You Been Exposed to High Enough Levels to Fail a Drug Test?

The researchers have spoken and the consensus is clear: you may fail a drug test after inhaling passive pot smoke, but only under a specific set of circumstances, which have been highlighted above.

However, let’s give the research done at the University of Calgary a revisit – the findings which were published in Canadian Medical Association Journal Open state that depending on just two factors such as the intensity of the smoke and ventilation level in a room, it may take as little as 15 minutes for THC to register in the bloodstream of a non-pot smoker.

And, it may take up to 48 hours for this traceable amount to disappear completely.

To put it very bluntly, if your future career prospects depend on remaining drug free, then is it really worth the risk? How hard could it be to ensure that marijuana is nowhere near you a day or two before the drug test?

Summing it all up, there is a lot of research that still needs to be done on the effects of marijuana smoke in non-smokers, and what kind of impact it can have on drug tests in future.

Different offices may have different THC benchmarking limits in order to clear a subject of marijuana use, even if it was non-deliberate through second-hand inhalation.

Be smart – if you know for certain that a drug test is coming up or that it is your employer’s requirement to stay drug-free in order to not only gain professional progression but stay employed – stay away from all sources of marijuana smoke.

You definitely don’t want to purposefully volunteer to sit in a confined room where recreational smokers are huffing and puffing away – save it until you are free of any drug-test danger at work!

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