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Secondhand Marijuana Smoke Exposure

Secondhand Pot Smoke Risks and Drug Testing Implications

Doru Paul, MD, is triple board-certified in medical oncology, hematology, and internal medicine. He is an associate professor of clinical medicine at Weill Cornell Medical College and attending physician in the Department of Hematology Oncology at the New York Presbyterian Weill Cornell Medical Center.

Secondhand marijuana smoke can negatively affect the health of exposed non-pot smokers

We have heard about secondhand tobacco smoke exposure for many years, but with the legalization of marijuana in some states, concerns have been raised about secondhand marijuana smoke exposure as well. These concerns come from two angles. One concerns health. Could secondhand marijuana smoke exposure have a negative effect on the health of exposed non-users? And, for those who do not smoke marijuana but hang out with marijuana smokers, could this exposure affect drug testing? Is secondhand marijuana smoke dangerous or could secondhand pot smoke mess up your drug testing at work? These are important questions to be asking.

Possible Health Risks

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?  

Limitations in Studying Health Risks

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.

In a study of 43 children, age 1 month to 2 years, who were admitted to hospitals in Colorado from 2013 to 2015 for bronchiolitis, urine samples tested for marijuana metabolites revealed that 16% of the children had a detectable level of exposure to secondhand marijuana smoke.   Another study that provided a preliminary look at health outcomes of children living in homes where marijuana is used showed a “relatively strong. association. between indoor cannabis smoking and adverse health outcomes in children” indicating a significant need for further study.  

Effect on Blood Vessels

Tobacco smoke (either in smokers or inhaled as secondhand smoke) can clearly damage blood vessels, with the risk of heart attacks and peripheral vascular disease in people who smoke or are exposed to secondhand smoke only a few examples. Research shared at the American Heart Associations (AHA) Scientific Meetings in 2014 suggested that secondhand marijuana smoke should likely be considered a public health problem.

A Significant Cause for Concern

Breathing secondhand marijuana smoke may cause as much damage to blood vessels as secondhand tobacco smoke.

This research looked at the effect of secondhand marijuana smoke on blood vessels, albeit in rodents. Rats that were exposed to secondhand marijuana smoke had a 70 percent reduction in blood vessel function. (These results were the same for rats exposed to marijuana smoke containing THC as those not, so it was considered likely that THC alone wasn’t the culprit.)  

Of even more concern was that whereas blood vessel function returned to normal after 40 minutes for rats exposed to secondhand tobacco smoke, this wasn’t the case for the marijuana smoke group; in the rats exposed to secondhand marijuana smoke, blood vessel function remained affected after this interval.

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.

Of course, the next step is determining the significance of reduced blood vessel function, something which has been linked to atherosclerosis and heart attacks.

Harmful Chemicals

Another concern surrounds the harmful chemicals in cigarette smoke. Tobacco smoke and marijuana are chemically alike, and therefore many of the harmful chemicals in cigarette smoke are likely to be found in marijuana smoke. We could make assumptions based on this evidence—that the cancer-causing chemicals in secondhand tobacco smoke which result in 34,000 deaths per year in the United States are also released in marijuana smoke—but until we have further studies, no one can say for sure.

In one study, levels of ammonia were 20 times higher in secondhand marijuana smoke than secondhand tobacco smoke. Levels of hydrogen cyanide and aromatic amines were three times to five times higher in secondhand marijuana smoke than secondhand tobacco smoke. And like tobacco smoke, marijuana contains a number of carcinogens (compounds known to cause cancer) such as benzene, cadmium, nickel, and more.  

Accidental Ingestion

A final concern is not a risk related to marijuana smoke per se, but is a secondhand risk to those who are around those who smoke marijuana. Children and even dogs have suffered from the accidental ingestion of marijuana. From broken bongs that can cut, to the financial complications imposed on nearby nonusers (for example if a child has a parent who faces legal problems due to use), are all things that need to be considered by those who choose to smoke marijuana.

Effects of Secondhand Marijuana Smoke on Urine Drug Screens

Many people have questioned whether secondhand marijuana smoke in non-smokers can result in positive drug screens.

Though older studies seemed to say no, a 2015 study suggests that the answer is yes, in rare cases anyway.   That said, the yes deserves an explanation. It’s wasn’t easy for a non-user to have a positive test. In the study that said “yes,” non-users were subjected to what was called “extreme exposure”—heavy exposure in poorly ventilated rooms—something that an individual would clearly be aware of. Even in this type of situation, the chance of a “false positive” result rapidly decreased with time; drug screens would be normal in a matter of minutes or hours.  

The conclusion of one older study is that it would be improbable that people would unknowingly tolerate the nasty smoke conditions that would result in a positive test. What does this mean? If you are at risk of having a positive test, you’re probably hanging with the wrong crowd.

Public Health Impact

Certainly, the findings of changes in blood vessels with secondhand marijuana smoke raises concern about the public health impact of exposure, but a thorough understanding of risks, as well as preventive measures that should be taken, is lacking at the current time.

Scope of the Problem

It’s difficult to know how common secondhand marijuana smoke exposure is, most notably because it is illegal in many places. A 2015 study set out to examine this question by questioning people at two southeastern universities. Researchers found that:

  • 14.5 percent of participants allowed cigarette smoking in the home
  • 17 percent allowed marijuana smoking in the home
  • 35.9 percent allowed cigarette smoking in cars
  • 27.3 percent allowed marijuana smoking in cars

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.  

Exposure in Open-Air Stadiums

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.  

Accidental Ingestion in Children

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.  

Next Steps

As more states legalize marijuana, issues regarding secondhand exposure are likely to be examined in more depth.

For Non-Users: Avoid secondhand marijuana smoke. If your loved ones use, ask them to use away from you, and certainly not in a poorly ventilated space.

For Users: Remember that legal doesn’t mean harmless. Consider the risk of secondhand smoke to non-smokers nearby, as well as the risk to children. Driving while under the influence of marijuana has the potential to result in injuries to both self, and other passengers in the car, as marijuana users are roughly 25 percent more likely to crash.   And, keep in mind that long-term use of marijuana can result in addiction in some people.

A Word From Verywell

While many people use marijuana recreationally, we can’t dismiss its possible benefit to people suffering from medical conditions such as cancer. Hopefully, now that marijuana is legal in many places, studies can further define its possible benefit in comparison with potential risks. That said, priority should be given to protect non-smokers from the effects of exposure. Edibles may eliminate the concern over secondhand marijuana smoke exposure, but accidental ingestion remains a concern, and those who choose this route and are around children should take precautions recommended for any substance that could cause poisoning.

How does secondhand marijuana smoke exposure affect the health of nearby non-pot smokers, and what impact does this have on drug testing?

What are the side effects of secondhand marijuana smoke?

Marijuana, the dried leaves and flowers of the cannabis plant, is known for its psychoactive properties. When a person smokes or ingests it, they experience a high. But what about secondhand smoke?

When a person does not smoke marijuana themselves but instead inhales the smoke that someone else breathes out, this is called secondhand marijuana smoking. Some people may be concerned about the risks of breathing this secondhand smoke.

Keep reading to learn more about the effects that secondhand marijuana smoke can have on a person and the possible risks.

Share on Pinterest A person is unlikely to get high from breathing in secondhand marijuana smoke.

Studies have shown that although possible, it is unlikely that a person who breathes in secondhand marijuana smoke will get high. A high that an otherwise sober person experiences when they are near someone under the influence of recreational drugs is known as a contact high.

The chance of a person becoming high after inhaling secondhand marijuana smoke can increase if they are very close to someone who is smoking. The risk also increases if the person smoking is using marijuana with a higher tetrahydrocannabinol (THC) level.

THC is one of several chemical compounds in the cannabis plant, which are called cannabinoids. It is THC that causes the mind-altering, or psychoactive, effects of weed. Naturally, a higher level of THC means a more potent effect.

If there is poor or no ventilation, the likelihood of a person becoming high from the surrounding smoke drastically increases, too.

In short, for a contact high to be possible, a person would need to be in close contact with highly concentrated marijuana smoke for an extended period in a poorly ventilated area.

People who inhale secondhand marijuana smoke may feel the following side effects:

  • burning, itchy, or red eyes
  • dry mouth
  • headache
  • coughing
  • increased appetite
  • rapid heartbeat
  • anxiety
  • euphoria
  • lightheadedness
  • a sensation of time slowing
  • restlessness
  • paranoia
  • tiredness
  • nausea

It is also possible that a person who has had exposure to high levels of marijuana smoke in a nonventilated area may experience slight impairments in their memory and motor skills. This effect can be dangerous if a person is driving or operating machinery.

Exposure to secondhand marijuana smoke carries some other risks, including:

Drug tests

Some workplaces require employees to undergo regular drug tests to make sure that they are drug-free and fit to work. Depending on the sensitivity of the drug test, a positive result may be possible in people who have not directly consumed marijuana but have inhaled secondhand smoke.

In one study, researchers tested urine samples from nonsmokers after they spent an hour in proximity to people smoking marijuana. The researchers found that people who were near to marijuana smokers in poorly ventilated areas did test positive for THC in their urine, based on “commonly utilized cutoff concentrations.”

However, the lack of ventilation and strength of the marijuana had a significant effect on the results. Also, the drug tests took place over the period straight after the participants had inhaled the smoke.

Heart health

Although the effects of secondhand cigarette smoke are well-known, experts know little about the associated health risks of secondhand marijuana smoke.

A 2016 study looked into the effects of secondhand marijuana smoke in rats. The researchers found that after a minute of exposure, the femoral artery’s response to increased blood flow became impaired for 90 minutes. In comparison, with cigarette smoke, this effect lasted only 30 minutes.

It is possible to conclude from these findings that secondhand marijuana smoke could have negative effects on the heart. However, researchers must continue to study this before making any firm conclusions.

In children

A study into the effect of secondhand marijuana smoke on 83 children with parents who smoke found that almost half of the children had biological evidence of exposure to marijuana.

Although there was no evidence to link secondhand marijuana smoke to health issues in these children, the results are concerning, given the presence of potentially harmful chemicals in marijuana smoke.

Marijuana cigarettes contain various toxins and tars that are also present in tobacco cigarettes, leading researchers to believe that secondhand marijuana smoke possibly carries some of the same health risks as secondhand cigarette smoke. More research is necessary to confirm this, though.

Some people may worry about the side effects of secondhand marijuana smoke. Learn more about the potential risks of inhaling secondhand marijuana smoke here.