Experts are still learning more about secondhand cannabis (or marijuana) smoke, but the risks of toxic smoke are already evident. And these risks appear greater for children, pregnant people, or those with chronic disease. Secondhand smoke from cannabis can also make you high or fail a drug test. Let’s take a closer look at how your exposure to other people’s cannabis use can affect you.
Can you get a secondhand high from marijuana smoke?
Yes, it’s possible to get high from secondhand cannabis smoke. But it depends on the amount of your exposure to THC, or tetrahydrocannabinol, the active part of cannabis that causes the high. A secondhand high also depends on the amount of ventilation in the room. For example, spending an hour in an unventilated room with cannabis smoke could be enough to get a contact high. And it could also affect a drug test.
Will secondhand marijuana smoke make me fail a drug test?
Possibly. It is possible for secondhand cannabis smoke to cause high enough drug levels to lead to a positive drug test. It depends on the amount of exposure and ventilation in the space you are in. And it may be more likely if you’re in a small, unventilated room with a heavy amount of cannabis smoke.
One study found that half of children exposed to cannabis smoke at home had positive levels of THC in their urine. So, it’s possible for you to have a positive drug test from secondhand smoke.
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What are the adverse effects of secondhand marijuana smoke?
Research is limited on this, but secondhand cannabis smoke contains many of the same toxic chemicals as smoking it yourself. And exposure to it likely carries a similar risk.
We know a lot about the harms of secondhand smoke from tobacco products like cigarettes. Secondhand smoke increases the risk of:
- Lung damage
- Heart disease
- Lung cancer
- Pregnancy complications
Understanding this helps to know the less-studied risks of secondhand cannabis smoke.
This is especially worrisome for at-risk populations such as children or those with other chronic medical conditions.
Lung damage
Any kind of smoke can damage your lungs, including cannabis smoke. When cannabis, or tobacco, or anything else is burned, it releases toxic chemicals. This may increase your risk of chronic bronchitis symptoms.
Studies suggest that when compared to tobacco smoke, smoking cannabis may not have as high risk for lung damage. But this may also depend on how much someone uses cannabis. For example, mild cannabis smokers may have less risk than heavy smokers.
Cancer
Heavy cannabis use through smoking can increase risk of cancer. Smoked cannabis, just like smoked tobacco, contains cancer-causing chemicals. And your risk will depend on how much and how often you smoke.
A study looking at risk over 40 years showed that heavy cannabis use was associated with more than twice the risk of developing lung cancer. The long-term effects of light or occasional cannabis use are still unclear.
Heart disease
There is limited research on the cardiovascular risks of cannabis. But some early data shows that there are adverse heart risks. Exposure to cannabis smoke may put you at greater risk of:
- A higher heart rate
- Elevated blood pressure
- Arrhythmia (irregular heart rhythm or extra heart beats)
- Increased risk of blood clot, heart attack, or stroke
The research on long-term effects of cannabis is ongoing.
Brain effects
There is also limited data on the long-term effects that cannabis has on the brain. Early research has shown mixed results. Some studies have shown that cannabis can decrease the size of your brain and affect various functions. Those most at risk seemed to be adolescents. And the areas of the brain most affected were responsible for:
- Memory
- Learning
- Impulse control
- IQ
Other studies show no effects on the size of the brain at all. More research is needed to determine the impact cannabis smoke has on the brain.
Pregnancy risks
Cannabis smoke can also affect a growing baby in pregnancy. Risks can include:
- Stillbirth
- Preterm birth
- Developmental delays
- Growth problems (low birth weight)
The bottom line
Experts are still learning about the effects of secondhand cannabis smoke. Known toxins and heavy exposure may increase the risk of cancer, heart, and lung disease — especially for young children or other at-risk groups. Brain and pregnancy effects are possible, too. In a poorly ventilated room with heavy exposure, secondhand cannabis smoke can be absorbed as if you are smoking it yourself. This could lead to making you feel high or failing a drug test.
If you or someone you know struggles with substance use, help is available. Call SAMHSA’s National Helpline at 1-800-662-HELP (4357) to learn about resources in your area.
References
American Lung Association. (2022). Marijuana smoke.
Callaghan, R. C., et al. (2013). Marijuana use and risk of lung cancer: A 40-year cohort study. Cancer Causes & Control.
