The idea that you can get high just from being around someone smoking cannabis is one of the most persistent myths in weed culture. It’s the classic “contact high” theory—where people believe that simply inhaling secondhand cannabis smoke in a closed environment can leave them stoned. But how much truth is there to this? Let’s break it down.
The Science of Secondhand Smoke and THC Exposure
First, let’s talk about what’s actually in secondhand cannabis smoke. When a person smokes a joint, blunt, or bowl, they inhale a mix of cannabinoids, including THC (the psychoactive compound responsible for the “high”), along with other plant compounds. As they exhale, some THC is released into the air, but it’s in a much lower concentration than what they initially inhaled.
Studies have shown that passive exposure to cannabis smoke can lead to trace amounts of THC in the bloodstream, but it requires very specific conditions. In a 2015 study published in Drug Testing and Analysis, researchers found that being in an unventilated, enclosed space with heavy cannabis smoke for an extended period could result in a mild presence of THC in the system. However, the levels detected were nowhere near high enough to cause actual intoxication.
In other words, unless you’re sitting in a hotboxed car or a completely sealed room filled with thick cannabis smoke for hours, the chances of getting high from secondhand exposure are extremely low.
The Hotbox Effect: Is It Real?
If you’ve ever been in a hotboxed car or a tiny, unventilated room where people are lighting up, you might have felt something—maybe a little lightheaded or relaxed. But was that an actual high? The answer is complicated.
Hotboxing can increase the concentration of THC in the air, but even in extreme cases, the amount you’d passively inhale is much lower than what a smoker is directly consuming. A study from The Journal of Analytical Toxicology tested this by placing non-smokers in a hotboxed environment with heavy cannabis use. The results? Some participants had slight traces of THC in their urine afterward, but none reported feeling high.
What’s more likely happening in these scenarios is a placebo effect combined with mild oxygen deprivation. The body’s response to a smoky, low-oxygen environment can sometimes mimic feelings of being high—like dizziness or lightheadedness—but it’s not the same as actually consuming THC.
The Legal and Practical Implications
A lingering concern for non-smokers, especially in places where cannabis is legal, is whether passive exposure could cause them to fail a drug test. The good news? Most drug tests look for THC metabolites, which only appear in significant amounts after direct cannabis consumption. The trace exposure from secondhand smoke is so minimal that it’s highly unlikely to trigger a positive result.
For parents, landlords, and those who prefer to avoid cannabis, the bigger issue with secondhand smoke is irritation from combustion byproducts rather than any intoxicating effects. Smoke of any kind—whether from cigarettes, cannabis, or even incense—can be an irritant to the lungs, especially in enclosed spaces.
Final Verdict: Myth Busted (Mostly)
So, can you get high from secondhand cannabis smoke? The short answer: not really. While extreme conditions (like a tightly sealed hotbox) might result in a minuscule THC presence in your system, it’s nowhere near enough to produce a true high. The classic contact high story? Mostly a myth.
That said, if you’re in a smoke-heavy environment and feel a little off, it’s more likely due to lack of oxygen or mild sensory effects rather than actual THC intoxication. And if you’re worried about drug tests or secondhand exposure, rest easy—it takes direct consumption to have a real impact.