Many people have questioned whether secondhand marijuana smoke in non-smokers can result in positive drug screens.
There are difficulties in evaluating potential hazards of secondhand marijuana smoke; not the least of which is that it is illegal in many areas, making studies difficult. Another is that the potency of marijuana has changed over time; the joints smoked by hippies in the 60’s aren’t the same as those smoked today. That said, several risks and potential risks have been identified.
Of course, this study evaluated only a subset of people, but the take away message is that many people are likely exposed to secondhand marijuana smoke.
We know that personal use of marijuana carries some health risks but what about non-users who are exposed to secondhand marijuana smoke? Do adults or children who are exposed need to worry?
Sanja Jelic, MD, is board-certified in sleep medicine, critical care medicine, pulmonary disease, and internal medicine.
While often we look at studies like this thinking that a lot of smoke over an extended period of time is to be most feared, a 2016 study made this approach questionable. It was found that even one minute of secondhand marijuana smoke could impair vascular endothelial function in rats. Even though we don’t know whether these results on rats reflect what happens in humans, knowing that vascular endothelial dysfunction underlies a leading killer in the U.S. (endothelial dysfunction leading to heart attacks), this information is worth investigating further.
While accidental ingestion of marijuana is a separate issue from secondhand smoke, we would be remiss to not mention it here. A 2017 systematic review published in the Journal of Pediatrics concluded that accidental ingestion of marijuana by children is a serious public health concern, and that physicians and the public should be aware of this concern in children who develop the sudden onset of lethargy or loss of coordination.
Again, it must be noted that studies looking at the potential impact of secondhand marijuana smoke are limited. A 2019 evaluation looked at the effect of secondhand marijuana smoke on the health of police officers working at open-air stadium events. Findings included detectable levels of THC in personal and area air samples, the presence of THC in the urine of 34 percent (but negative blood tests), and symptoms potentially attributable to the exposure including dry, red eyes, dry mouth, headache, and coughing. The officers, however, did not experience a “high” related to the exposure.
Of course, the next step is determining the significance of reduced blood vessel function, something which has been linked to atherosclerosis and heart attacks.
How does secondhand marijuana smoke exposure affect the health of nearby non-pot smokers, and what impact does this have on drug testing?
Under the unventilated, “hot box” condition, the nonsmokers showed slight impairments on cognitive tests, reported feeling high, and had detectable levels of THC in their blood and urine for up to 22 hours post-exposure. Those in the ventilated condition had much lower levels of THC in their blood, did not feel impaired or high, and did not test positive for THC in their urine.
Studies in the 1980s showed that such “social exposure” to pot smoke could trigger positive drug tests for cannabis’ main psychoactive ingredient, tetrahydrocannabinol (THC). But such studies had several limitations. They used marijuana that had much lower potency than the pot available today and they failed to account for normal levels of ventilation in rooms. They also did not examine how people may feel or behave after such exposures.
In the first study of its kind, Herrmann’s team recruited about 20 healthy people between the ages of 18 and 45, including some who smoked marijuana and some who didn’t use the drug. The researchers tested the participants’ blood, saliva, urine and hair samples for cannabis biomarkers, and then asked six smokers and six nonsmokers to relax in a Plexiglas and aluminum smoke chamber about the size of a dorm room. Participants underwent two separate sessions, each an hour long.
But the unventilated room is not representative of most real-life situations, the researchers said. “We modeled the worst-case scenario,” Herrmann said. “You are in an enclosed room for an hour with 15 grams of cannabis being smoked.”
People who are exposed to secondhand marijuana smoke may feel a bit of the “high” that comes with using the drug, a new study finds. They may also feel unable to think clearly, and they may even have detectable levels of the drug in their urine or blood. But all of this happens only if they are exposed to marijuana smoke under severely unventilated conditions, the study found.
The researchers gave each of the six smokers 10 marijuana cigarettes, each containing 1 gram of high-potency weed, and instructed them to smoke at their leisure for the hour while the six non-smokers sat by their side in the chamber.
“Our results are pretty consistent with what we expected,” Herrmann said. The new findings confirm “it’s really hard to get a positive [drug test result] from passive smoke unless you’re in an extreme scenario,” he said.
Cannabis is the world’s most commonly used illicit drug. It is often smoked in small, enclosed spaces with poor ventilation, according to the study.
“If you’re going to breathe in enough passive cannabis smoke to feel high and potentially be slightly impaired, you could fail a drug test,” said Evan S. Herrmann, the study’s lead author and postdoctoral fellow in psychiatry and behavioral sciences at Johns Hopkins School of Medicine. “But this only happens under a very extreme situation.”
People who breathe in a lot of secondhand marijuana smoke could test positive on a drug test, a new study finds.