Monday Myth Buster #1
Secondhand High: Can Non-Users Absorb THC Through Passive Exposure?
As cannabis legalization spreads across the world, a new question has emerged: Can non-users get high from secondhand exposure to cannabis smoke? Stories of people claiming to feel “stoned” just from being around smokers are common, but is there scientific truth behind these claims, or is it simply placebo? This essay explores the science behind secondhand THC exposure, the real-world scenarios that might increase or minimize its effects, and the legal and workplace implications of passive cannabis exposure.
The Science of Secondhand Cannabis Smoke: Can You Really Get High?
Research has long established that secondhand tobacco smoke can have harmful health effects, but secondhand cannabis smoke is a newer area of study. The main psychoactive compound in cannabis, tetrahydrocannabinol (THC), is released into the air when cannabis is smoked or vaporized. This raises the question of whether non-users can passively inhale enough THC to experience psychoactive effects.
A controlled study published in The Journal of Analytical Toxicology exposed non-users to secondhand cannabis smoke in a confined, unventilated space. The results showed that under extreme conditions—such as a small, enclosed space with multiple smokers—THC levels in non-users’ blood and urine were detectable, and some participants reported mild subjective effects like dizziness or slight intoxication. However, when the same experiment was conducted in a well-ventilated room, THC absorption was minimal, and participants did not report any noticeable effects (Cone et al., 2015).
A similar study published in Drug Testing and Analysis examined whether non-users could test positive on a drug test after passive exposure. In extreme cases, non-users did test positive for THC on urine tests taken shortly after exposure, but these levels were generally below the threshold for standard workplace drug testing (Herrmann et al., 2015). This suggests that while passive cannabis exposure can result in some THC absorption, the chances of experiencing significant psychoactive effects or failing a drug test are low unless exposure is prolonged and in a confined environment.
Real-World Scenarios: Enclosed vs. Open Spaces
While laboratory studies provide useful insights, real-world cannabis exposure scenarios vary widely. The setting plays a major role in determining the extent of THC absorption for non-users.
Enclosed Spaces (e.g., cars, small rooms, nightclubs): Studies indicate that poorly ventilated, enclosed spaces increase the concentration of THC in the air, making it more likely for non-users to inhale enough to experience mild psychoactive effects. In one real-world study, researchers found that THC levels in the air of a parked car with the windows rolled up reached levels similar to those in the controlled laboratory studies (Watson et al., 2016).
Well-Ventilated Areas (e.g., outdoor concerts, open-air patios): Outdoor or well-ventilated environments significantly reduce THC exposure. A study conducted at a cannabis consumption event found that THC concentrations in the air decreased rapidly in outdoor conditions, making passive intoxication highly unlikely (Moore et al., 2018).
Vaporized Cannabis vs. Smoked Cannabis: Vaporizing cannabis instead of smoking it may further reduce secondhand exposure risks. Unlike smoking, vaporization releases fewer combustion byproducts and less sidestream smoke, meaning less airborne THC for non-users to inhale (Spindle et al., 2017).
Legal and Workplace Implications of Passive Exposure
The question of secondhand cannabis exposure isn’t just scientific—it also has important legal and workplace consequences.
Workplace Drug Testing: Many workplaces still conduct drug tests, particularly for employees in safety-sensitive positions. While studies show that extreme secondhand exposure can lead to low but detectable THC levels in urine, the likelihood of failing a drug test remains low under normal conditions. However, legal disputes have emerged where employees claimed secondhand exposure led to positive drug test results, highlighting a potential gray area in workplace policies (Huestis, 2016).
Public and Legal Considerations: Some jurisdictions have extended public smoking bans to include cannabis, treating it similarly to tobacco in terms of secondhand exposure concerns. For instance, states like Colorado and California have laws prohibiting cannabis smoking in public spaces, partly to prevent unintended secondhand exposure (Pacula et al., 2017).
Child Welfare and Custody Cases: Courts have begun addressing whether parental cannabis use could impact custody arrangements due to concerns over secondhand exposure. While no studies conclusively show harm to children from passive cannabis exposure, legal systems err on the side of caution, particularly when cannabis is smoked indoors (Wang et al., 2018).
So, can you get high from secondhand cannabis smoke? The science suggests that while passive THC absorption is possible, non-users are unlikely to experience significant psychoactive effects unless exposed in enclosed, unventilated spaces with heavy cannabis smoke. The risk of failing a drug test due to secondhand exposure is also minimal but not impossible under extreme conditions. As cannabis use becomes more socially accepted and legally complex, understanding these nuances will be essential for individuals, employers, and lawmakers alike.
