Is second-hand cannabis smoking harmful?

In 1998, Ross Rebagliati won the gold medal in the men’s snowboard giant slalom at the Olympic Winter Games in Nagano, Japan. The day after his victory, he was stripped of his medal after testing positive for marijuana. Rebagliati’s urine test showed 17.8 nanograms in his system, while the limit at the time was 15 nanograms.

Rebagliati claimed that the positive test was caused by secondhand smoke he inhaled at a party the night before he left for the Olympics, and in a controversial appeal, Rebagliati was reinstated with his gold. Still, the event left many questions – how strong is second-hand cannabis smoke?

Aside from the problem of getting accidentally high, there are respiratory risks associated with smoking weed second-hand. Let’s look at the effects of second-hand cannabis smoke, how it compares to second-hand tobacco smoke, and whether second-hand cannabis vapor poses any health problems.

Risks associated with passive smoking of cannabis

Research tells us that second-hand cannabis smoking poses two significant risks for non-smokers. For starters, individuals who do not actively smoke but inhale second-hand weed smoke can become easily intoxicated by THC. The other problem is that cannabis smoke contains hundreds of different types of chemicals and particles (tiny particles of matter) that can be toxic to those who inhale it – secondhand or not.

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Back in 2014, a group of Johns Hopkins researchers conducted a study to learn more about the effects of second-hand cannabis on non-smokers.

Researchers placed six cannabis smokers and six non-smokers in a small sealed chamber for three hour-long sessions.

• In the first session, the chamber was unvented and the smokers were given joints containing 5.3% THC to smoke.
• In the second session, the chamber remained unvented and the smokers consumed joints containing 11.3% THC.
• The final session kept fans running in the chamber while smokers resumed smoking joints containing 11.3% THC. The ventilation system is designed to emulate typical residential air conditioning conditions based on building HVAC standards.

The results revealed two critical factors: aeration and THC potency both play a role in determining whether non-smokers returned positive marijuana drug tests.

In the first session, a non-smoker produced a positive drug test with THC levels around the 20 nanogram/mL limit (although this is significantly lower than the state limit for a positive screen, which is 50 nanograms/mL). In the second session, four non-smokers produced positive tests up to 22 hours after exposure.

No participant in the third session (the ventilated session) had positive tests, showing that room ventilation played a role in reducing exposure to secondhand smoke. Further analysis showed that those who inhaled secondhand smoke during the first two sessions experienced mild cognitive impairment.

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However, even the authors of the study acknowledge that the first two sessions of the study were somewhat unrealistic. One researcher described these test conditions as a “worst-case scenario” because these conditions “couldn’t happen to anyone without his or her being aware of it.” In other words, the study tested the likelihood of secondhand smoke poisoning by creating an extreme situation that was unlikely in reality.

The study’s conclusion also acknowledged that positive drug tests in non-smokers would be unlikely under more normal circumstances, limited to the day after immediate exposure, and would only occur if exposure to secondhand smoke was extreme (i.e., in a confined space with no ventilation). ). The results of the third testing session are therefore perhaps most applicable to real life: In a ventilated, air-conditioned space, those exposed to second-hand weed smoke would not test positive for THC.

Particulate matter increases

A more recent 2022 study looked at the effects of bong smoking and found that bong smoke increased the amount of particulate matter — microscopic solids or liquid droplets — in indoor air by up to 1,000 times.

In a session monitored 12 hours after quitting smoking, the concentration of particulate matter in the air remained more than ten times higher than the concentration in the room before smoking. The researchers pointed out that even 15 minutes of bong smoke produced a particle concentration more than twice the Environmental Protection Agency’s air quality threshold. Exposure to particulate matter above the proposed guidelines has been linked to reduced lung function and increased mortality from lung cancer and heart disease.

Although there are conjectures about the health effects of secondhand smoke, no research has yet established a direct causal relationship between secondhand smoke and any disease or disorder.

Cannabis clinician Dr. Benjamin Caplan, MD, The founder and Chief Medical Officer of the IBD Clinic and Foundation emphasizes that available research needs to be contextualized and that assumptions and biases can lead people down the wrong path.

He points out that public health science has repeatedly shown that near-constant exposure to air pollution in urban settings is associated with higher risk of morbidity and mortality.

“It’s hard to argue convincingly that the dangers of second-hand cannabis smoking pose any greater harm than the ubiquitous smoke and smog of modern city life,” he reflected. “Whether or not second-hand cannabis smoke represents a significant decrease in toxicity – and the debate is warranted and ongoing – it’s probably literally a small drop in a big bucket.”

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Second-hand cannabis smoke vs. second-hand tobacco smoke

There is a common notion that weed smoke is not as harmful as tobacco smoke. As many as 27% of young adults believe that exposure to second-hand cannabis is safe. However, there is evidence that both second-hand cannabis and tobacco smoke can trigger asthma attacks, lung irritation and respiratory infections.

Cannabis smoke can also produce more particulate matter than tobacco. In the 2022 bong smoking study mentioned above, researchers discovered that bong smoke generates four times as much particulate matter as cigarettes. They pointed out that this air pollution could potentially contribute to many health problems for those exposed to secondhand smoke, let alone the smokers themselves.

However, research also suggests that tobacco smoke, whether second-hand or otherwise, is significantly more carcinogenic than cannabis smoke. Cannabis smoke has not been causally linked to tobacco-related cancers such as lung, colon, or rectal cancer.

One study speculates that tobacco smoke is more likely to cause lung cancer than cannabis smoke due to the beneficial activity of compounds found in the cannabis plant. The pharmacological properties of cannabinoids in weed can minimize carcinogenic (cancer-causing) activity in several ways: THC, for example, can inhibit the activity of certain enzymes needed to activate the carcinogenic compounds in smoke. However, large-scale clinical trials comparing cannabis and tobacco smokers are needed to learn more and confirm this theory.

Overall, Dr. Caplan that much of the research on the risks of secondhand smoke has been loosely applied to secondhand smoke of cannabis without sufficient evidence.

“In chemical terms, nicotine is a toxic toxin with a plethora of negative effects ranging from promoting cancer and respiratory disease to cardiovascular damage and psychological, oral, reproductive and addictive consequences,” he said . “These effects are rumored to be relevant to cannabis, although the evidence is far less conclusive.”

Is second-hand cannabis vapor harmful?

Given the popularity of vaping, it’s worth diving into the second-hand data on the effects of weed vapor. From the available evidence, second-hand vaping can also pose some risks.

In a recent study conducted in a well-ventilated cannabis dispensary and consumption room where vaping and dabbing were permitted (but smoking was prohibited), researchers found that vaping produced high enough concentrations of particles to adversely affect cardiovascular health. The concentration of particulate matter in the air was about 28 times higher when the lounge was open and active smoking than when the shop was closed. The highest daily particle concentrations corresponded to the busiest hours.

“While vapor has fewer potential irritants than smoke, it can represent a far denser cloud of material,” Caplan said. However, Caplan also points out that cannabis vapor is thought to produce fewer toxic compounds than cannabis smoke.

“Both smoke and vapor contain tar, but they have different compositions,” explains Caplan. “Steam is formed at lower temperatures than smoke, so it has fewer chemical reactions and fewer harmful compounds are often produced.”