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.

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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.

Learn more about what it feels like to be high on marijuana here.

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.

Learn more about cannabis and drug testing here.

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.

Learn more about cannabis and pregnancy here.

Current studies indicate that secondhand marijuana smoke is unlikely to affect people who experience limited exposure in a well-ventilated environment. However, researchers need to carry out more studies to determine the effects that secondhand marijuana smoke can have on a person.

It is also possible that people with asthma or other breathing issues could be more prone to negative side effects from inhaling secondhand marijuana smoke. However, there is currently no research to support this theory.

In general, contact with secondhand marijuana smoke is unlikely to cause any harmful effects. However, a person who is around people smoking marijuana should be cautious, as there may be unknown risks.