Is Secondhand Cannabis Smoke Harmful? – All You Need To Know

by | Jun 5, 2023 | Health | 0 comments

Can You Get High Even If You Don’t Smoke?

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A study conducted by Johns Hopkins researchers in 2014 aimed to investigate the effects of secondhand cannabis smoke on non-smokers. The study involved placing six cannabis smokers and six non-smokers in a small sealed chamber for three one-hour sessions. During the first session, the chamber was unventilated, and the smokers consumed joints containing 5.3% THC. In the second session, the unventilated chamber again housed smokers who consumed joints with 11.3% THC. In the final session, ventilation fans were activated, simulating typical home air-conditioning conditions. Smokers consumed joints with 11.3% THC during this ventilated session.

The results indicated that two factors, ventilation and THC potency, influence whether non-smokers test positive for marijuana. In the first session, one non-smoker tested positive with THC levels near the 20 nanograms/mL cutoff (though significantly lower than the federal cutoff of 50 nanograms/mL for a positive screen). In the second session, four non-smokers produced positive tests up to 22 hours after exposure.

In contrast, no participants in the ventilated session (session three) showed positive test results, highlighting the role of room ventilation in reducing secondhand smoke exposure. Further analysis revealed that individuals exposed to secondhand smoke during the first two sessions experienced mild cognitive impairment.

However, the authors of the study themselves acknowledge that the first two sessions of the research were somewhat unrealistic. One researcher described those test conditions as a “worst-case scenario” since they would be unlikely to occur without the individual being aware of it. Essentially, the study aimed to assess the possibility of secondhand smoke intoxication by creating an extreme situation that is improbable in real life.

The study’s conclusion also admits that under more normal circumstances, positive drug tests among non-smokers would be unlikely and limited to the day immediately following exposure, only occurring when exposed to extremely high levels of secondhand smoke (e.g., in a closed room without ventilation). As a result, the findings from the third testing session are likely the most relevant to real-life situations: In a room with proper ventilation and air conditioning, individuals exposed to secondhand cannabis smoke would not test positive for THC.

Risks From Secondhand Cannabis Smoke

The dangers related to secondhand cannabis smoke Studies indicate that secondhand exposure to cannabis smoke poses two notable risks for non-smokers. Firstly, individuals who are not directly smoking but inhale secondhand marijuana smoke may experience mild THC intoxication. Additionally, cannabis smoke comprises numerous chemicals and particulates, which can be toxic to those who breathe it in, regardless of whether they are exposed to it secondhand or directly.

Impact of Increased Particulate Matter From Bong Smoking

A more recent study conducted in 2022 investigated the effects of bong smoking and revealed a significant rise in the presence of particulate matter, which consists of microscopic solids or liquid droplets, by up to 1,000 times in the surrounding air.

Even after a 12-hour period following smoking cessation, the concentration of particulate matter remained over ten times higher than the pre-smoking levels in the room. The researchers emphasized that just 15 minutes of bong smoke produced a particulate concentration exceeding twice the hazardous air quality threshold set by the Environmental Protection Agency. Exposure to particulate matter above recommended guidelines has been associated with decreased lung function and increased risks of lung cancer and heart disease.

However, while there is speculation about the impact of secondhand cannabis smoke on health, no research has established a direct causal link between secondhand smoke and any specific illness or disorder.

Dr. Benjamin Caplan, a cannabis clinician and founder of CED Clinic and CED Foundation, emphasizes the need to contextualize available research and cautions against assumptions and biases that may mislead people. He points out that public health science consistently shows that continuous exposure to air pollution in urban environments is associated with higher morbidity and mortality risks.

Reflecting on the topic, Dr. Caplan suggests, “It is difficult for anyone to convincingly argue that the dangers of secondhand cannabis smoke pose greater harm than the constant presence of smoke and smog in modern city life. While the debate continues regarding the meaningful toxicity of secondhand cannabis smoke, it is likely, in literal terms, a minor issue compared to the larger problem at hand.”

Impact of Secondhand Cannabis Vape Smoke:

With the increasing popularity of cannabis vaping, it is important to examine the potential harm of secondhand weed vapor. Available evidence suggests that secondhand vapor may carry certain risks.

A recent study conducted in a well-ventilated cannabis dispensary and consumption space, where vaping and dabbing were allowed but smoking was prohibited, revealed that vaping produced high concentrations of particulates that could impact cardiovascular health. The concentration of particulates in the air was approximately 28 times higher during operational hours when people were actively vaping compared to when the business was closed. Peak levels of particles coincided with the busiest periods.

Dr. Benjamin Caplan, a cannabis clinician, acknowledges that while vapor contains fewer potential irritants than smoke, it may create a denser cloud of material. However, he also highlights that cannabis vapor is believed to generate fewer toxic compounds compared to cannabis smoke.

Caplan explains that both smoke and vapor contain tar but have different compositions. Vapor is produced at lower temperatures, resulting in fewer chemical reactions and often fewer harmful compounds.

In summary, while secondhand weed vapor may pose certain risks, it is generally considered to have fewer irritants and potentially harmful compounds than cannabis smoke. However, further research is needed to fully understand the effects and potential long-term consequences of secondhand weed vapor exposure.

Is Secondhand Cannabis Smoke Better Than Secondhand Tobacco Smoke?

The perception that weed smoke is less harmful than tobacco smoke is prevalent. Surprisingly, as many as 27% of young adults believe that exposure to secondhand cannabis smoke is safe. However, evidence indicates that both secondhand cannabis and tobacco smoke can trigger asthma attacks, lung irritation, and respiratory infections.

Interestingly, cannabis smoke may produce a higher amount of particulate matter compared to tobacco smoke. In a recent study on bong smoking in 2022, researchers discovered that bong smoke generated four times more particulate matter than cigarettes. This level of air pollution can potentially contribute to various health issues among individuals exposed to secondhand smoke, including the smokers themselves.

Contrarily, research suggests that tobacco smoke, whether firsthand or secondhand, is considerably more carcinogenic than cannabis smoke. Notably, cannabis smoke has not been directly associated with tobacco-related cancers such as lung, colon, or rectal cancer.

One intriguing study speculates that tobacco smoke is more likely to cause lung cancer than weed smoke due to the beneficial properties of compounds found in the cannabis plant. Cannabinoids in cannabis, such as THC, may inhibit the activity of enzymes necessary for activating cancer-causing components of smoke. However, extensive clinical studies comparing cannabis and tobacco smokers are required to gain further insights and verify this theory.

Dr. Caplan emphasizes that much of the research on the risks of secondhand tobacco smoke has been loosely applied to secondhand cannabis smoke without sufficient evidence. He highlights the toxic nature of nicotine, which is laden with adverse effects, including the promotion of cancer, respiratory disease, cardiovascular damage, and negative impacts on mental, oral, reproductive, and addictive health. While these effects are rumored to be relevant to cannabis, the evidence remains considerably less conclusive.

In summary, a comprehensive understanding of the risks associated with secondhand cannabis smoke compared to secondhand tobacco smoke requires further research and large-scale clinical studies. The chemical constituents of nicotine, a poisonous toxin, have been extensively studied, whereas the evidence regarding the potential harms of cannabis smoke is still inconclusive.

IMPORTANT: The information on this blog is for general informational purposes only and should not be considered as medical advice. Always consult a qualified healthcare professional for personalised medical advice. The authors of this blog are not medical professionals and disclaim any liability for the use of the information provide.

Enrico Bratta

Enrico Bratta

Medical cannabis professional based in Phuket, Thailand.


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Enrico Bratta

Medical cannabis professional based in Phuket, Thailand.