Most expectant mothers stop ingesting marijuana during their pregnancy, as the risks of cannabis use during pregnancy are well known. But if you live in a home where your partner or another member of the household smokes, especially around you, you could unknowingly be putting your unborn child in danger.

According to the CDC, “Secondhand marijuana smoke contains many of the same toxic and cancer-causing chemicals found in tobacco smoke. THC, the psychoactive or mind-altering compound in marijuana, may also be passed to infants through secondhand smoke.”

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Cannabis smoke might contain substances of heavy metals. These dangerous pathogens come from the plant absorbing it through the soil, cross-contamination during drying or some post-processing alteration to the flower itself.

A 2018 study indicated that cannabis smoke appears to contain endocrine disruptors, which have the ability to interfere with normal fertility function and developmental processes.

Heavy metals such as cadmium and arsenic and some pesticides are highly volatile and become carcinogenic when exposed to fire, the report added.

The dangers of secondhand tobacco smoke are well documented. But while we have reams of evidence regarding the harms of secondhand tobacco smoke, the actual impact of secondhand cannabis smoke is less known. The dearth of information is largely due to cannabis not being legal on the federal level, said Dr. Ken Weinberg of the Cannabis Doctors of New York. 

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“It’s very difficult. We’re not getting a lot of great studies because it’s schedule one substance,” he said. “I keep going back to the point that we need to make it legal so we can do well-designed, placebo-controlled studies.” 

Weinberg advises his pregnant patients not to consume cannabis of any kind while carrying. He also cautions them about the dangers of secondhand smoke, especially if their partner is a smoker.

“I think there’s a risk, and until we have more information I would be mindful of that risk,” he said. “If you’re pregnant, it’s best not to be around someone who is smoking.”

So how far is a safe enough distance?

“Ideally smoking should be outside,” Weinberg said. 

When it comes to talking with your partner about the potential dangers of secondhand smoke, Weinberg said it’s best not to be paternalistic in your approach. 

He goes about advising his patients the same way. 

“Doctors can have a paternalistic attitude. Patient autonomy is very important. Autonomy is an important part of the cannabis medical experience.”

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Although cannabis can be helpful in treating symptoms like morning sickness, physicians still advise against people who are pregnant consuming cannabis.

From a report published by the American Heart Association, “The impact on pregnant women and the developing fetus is also a significant concern. It has been very difficult to study the impact of marijuana smoking on the fetus because even in states where recreational marijuana is legal, there are still laws on the books requiring referral to child protective services for a positive marijuana screen at birth.”

Baby Centre, a UK-based resource for pregnancy and parenting information, says on their website that, “If you inhale cannabis while you’re pregnant, the drug can pass to your baby through the placenta. This may affect your baby’s brain, leading to problems with hyperactivity and learning as it grows.”

Additionally, they say, “If your partner smokes weed with tobacco, this is even more harmful for your baby. Even if your partner smokes in another room or out of an open window or door, you and your baby will still be breathing in the toxins. Breathing in second-hand tobacco and weed smoke may lead to your baby being born earlier and with a lower birth weight than expected,” according to Baby Centre.

So while cannabis can have many health benefits, it appears secondhand cannabis smoke poses a danger to pregnant people. More research needs to be done on the subject before the effects of secondhand cannabis smoke on a growing fetus can be fully understood, but to err on the safe side it may be wise to ask those you live with to consume non-smokable forms of cannabis (such as edibles or tinctures) throughout your pregnancy if you are expecting. 

Jordan Guinn is a published journalist with bylines in the San Francisco Chronicle, the Los Angeles Times, the Stockton Record and more. He’s covered everything from agriculture, to violent crime to water.