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Is it safe to consume cannabis during and after pregnancy?

Many pregnancy-related symptoms, such as increased stress levels, repeated bouts of nausea, and a limited appetite, are often effectively combated by cannabis in non-pregnant individuals. But is consuming cannabis a reasonable therapeutic strategy for expecting mothers who experience challenges during and after pregnancy?

Additionally, pregnancy-related complications don’t just disappear once the baby enters the world. Many postpartum mothers experience profound anxiety and depression, they’re left in pain, and sleep goes to hell.

Is there harm in consuming cannabis through the pregnancy and postpartum periods, and if so, what strategies exist to mitigate risks?

What’s the risk of cannabis use to the developing fetus?

In a 2020 study done in California, around 11% of women reported using cannabis while pregnant, a near doubling of pre-legalization levels: 6% vs. 11%. But one major limitation of this epidemiological study is that it doesn’t control for cannabis composition—it’s not strain-specific or controlled for THC levels.

This is just one study of many that are limited because they don’t capture CBD use, nor do they reliably consider the use of additional drugs such as nicotine and caffeine. Consequently, it’s difficult to parse out the effect of cannabis alone on birth outcomes and child development.

The effects of cannabis usage during pregnancy on the developing fetus and the child’s behavior later in life are inconsistent. In part, the timing of cannabis use during pregnancy may be associated with unique impacts. The cannabinoid type I (CB1) receptors that THC activates to make you feel high aren’t found in substantial numbers in the fetus until 19 weeks of gestation.

In rhesus monkeys, THC readily crosses the placenta and can be detected in fetal blood within 15 minutes of the mother’s use. That’s not to suggest the fetus can get stoned; it’s not until the third trimester that the fetus’ brain has the requisite structures for this effect, and even so, it would be a highly different experience.

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Still, CB1 receptors and the rest of the endocannabinoid system have a substantial role in brain development. For instance, they can influence how brain cells develop, tell them where to go, which ones to connect to, and what to look like. The activation of CB1 receptors plays an important role in brain development that could be substantially disrupted by THC if the mother consumes cannabis while pregnant. Or so the theory goes.

One alarming study of nearly 25,000 mothers found that 500 children born to cannabis-using mothers were lighter in weight, were more likely to arrive early (i.e., pre-term), and more likely to be admitted to the neonatal intensive care unit. Interestingly, these effects were present even when controlling for factors such as socioeconomic status.

Additionally, if the mother had traditionally been a cannabis consumer and stopped during pregnancy, these negative effects disappeared, suggesting that cannabis directly impacts fetal development.

Notably, these findings haven’t been consistently replicated. A recent 2020 study of California mothers found no clear impacts of cannabis use on these neonatal outcomes. Together, these findings highlight the immense variability in cannabis’ effects on the fetus and developing child.

Does diet have an effect?

For one, these are merely observational studies and therefore don’t control for things like frequency of use, dosing, or lifestyle differences, such as diet. While there’s little research on how diet interacts with cannabis and affects the developing fetus, one study identified a potential protective effect of dietary choline against harm caused by gestational THC exposure.

Choline is an essential nutrient found in many foods such as eggs, meat, and potatoes. The body can produce its own choline but it’s normally not enough, especially for the developing brain which requires choline synthesis for an important developmental brain chemical, acetylcholine.

A team led by Dr. Camille Hoffman, an OBGYN practitioner in Denver, Colorado, tracked maternal choline levels in over 130 women since 2013 and assessed their newborns after birth. Although they observed that cannabis use during the first trimester was associated with behavioral abnormalities, the children of cannabis-consuming mothers with the highest choline levels had better self-regulation, improved attention span, cuddled more, and bonded better with their parents.

In an interview with Dr. Hoffman, she’s quick to point out that increasing choline in one’s diet is not a sure path to safety. However, based on her research, Dr. Hoffman recommends that expecting mothers should consume around 900mg of choline daily through either diet or supplement to mitigate the potentially harmful effects of gestational THC exposure.

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Cannabis and other substances

When considering the research of moderate cannabis use among pregnant mothers, Dr. Hoffman stated that the effects observed on fetal brains are still subtle. “People make all kinds of good or bad decisions and [cannabis] doesn’t seem to be as bad as [other drugs of abuse],” she said. “Yes, there are emerging data that we should be using caution … but it’s probably not as bad as the things that we know are detrimental, such as alcohol.”

Yet, there are some factors that exacerbate cannabis’ effect on the developing fetus. Dr. Hoffman highlighted that using several substances may be substantially worse than one alone. For instance, in one study, the co-use of tobacco and cannabis had double the impairing effect on the infant’s ability to self-soothe compared to infants from tobacco-only users.

While this effect was more pronounced in girls, another study found that tobacco and cannabis co-use led to a more substantial dysregulation of the infant stress response in boys—males from cannabis + tobacco-using mothers had 35% lower cortisol responsivity and 22% lower responsivity from tobacco-only-using mothers compared to non-users. Why co-use of tobacco worsens outcomes in a sex-specific manner remains unknown, but it highlights the potential problems with using multiple substances to treat symptoms.

So while many mothers may use several medications to treat pregnancy-related symptoms—e.g., anxiety, nausea, sleep—Dr. Hoffman suggests that the interactions between all these medications may carry their own risks.

The effects of cannabis on brain development and mental health

Many lab animal studies have demonstrated that THC has harmful effects on brain development. In many instances, however, the studies only model extreme usage of high levels of THC and don’t accurately model more common usage patterns of traditional whole-plant cannabis.

Nonetheless, studies highlight the vulnerability to THC of brain regions involved in impulse control, executive functioning, emotional development, and reward processing. Consistent with THC impacting these brain regions, several of the more comprehensive assessments of gestational cannabis use have found that children of cannabis-using mothers are more likely to be impulsive, hyperactive, have poorer abstract reasoning, and worse executive functioning.

A child’s mental health may also be affected by maternal cannabis use. Ten-year-old children in one cohort self-reported higher levels of depression if their mothers engaged in heavy cannabis use during the first trimester. This is notable because approximately 70% of Colorado dispensaries recommend cannabis during the first trimester to help combat nausea.

Many parents are justifiably concerned about the long-term behavioral consequences of cannabis use, but controlled human experiments aren’t in the future. Correlation does not equal causation, so one must be careful placing causal blame on any one factor in complex behavioral outcomes.

Although some may attempt to limit risk by transitioning to products higher in CBD, scientists still have little understanding of the long-term consequences that CBD has on the more than 65 targets in the brain and body of the fetus. While the harm of maternal cannabis use is far from consistent, there is no clear evidence of safety either.

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What’s the exposure risk to a child from secondhand marijuana smoke?

Once the baby arrives, the newborn can still be exposed to cannabis through breastmilk and secondhand smoke. In one study, THC and its metabolites were detected in adults in trace amounts from secondhand cannabis smoke. While these low levels aren’t likely to be impactful to a child, repeated exposure to secondhand cannabis smoke can build up over time due to the fat-soluble nature of THC and other cannabinoids.

Another study demonstrated that despite the low level of THC transfer by secondhand smoke with a potency of 11.3% THC, it was sufficient to cause mild subjective effects in adults. However, these effects were minimized by improving room ventilation.

What’s the exposure risk from breast milk?

Breast milk is another source of cannabinoid transfer to the infant. THC can be detected in breast milk for up to 6 days after smoking. However, in some cases, there’s no transfer of THC at all. It’s unclear at this point what factors lead to the transfer of THC in some cases but not others.

Variability is also observed in the proportion of THC that gets transferred. One study found that the breast milk of regular cannabis-using mothers contained 2.5% of the 0.1 grams of about 23.2% THC-rich cannabis they inhaled. THC was detected within the first 20 minutes of inhaling and peaked around 1 hour after using. Importantly, the variability of THC transfer across mothers was immense, ranging from 0.4% (a little) to 8.7% (a lot).

There are no clear predictors at this time for where people will fall along this spectrum, but it is estimated that the infant exposure dose would be about 1,000 times lower than the mother’s. Whether that’s a significant amount to impact the child’s brain development remains unknown.

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Can cannabis help?

Despite the risk of transferring cannabinoids to the infant, there’s not always a simple right or wrong answer when considering whether to consume. Maternal bonding and infant care can be influenced by a number of factors, including the mother’s mental health and well-being.

Up to 85% of new mothers experience the “baby blues” within a couple weeks after giving birth, and around 15% develop clinical postpartum depression within the first year. Anxiety, poor sleep, and postpartum pain only add to challenges post-birth.

The most effective and safest strategies must be considered by balancing risk with benefit. Although there’s increasing evidence that these symptoms may be managed with CBD, that cannabinoid’s developmental effects remain considerably understudied relative to the known effects of THC.

Like many health and safety aspects of cannabis, there aren’t any definitive findings that guarantee its safety or harm. Instead, the true impacts likely fall somewhere between alarmist views perpetuated by medically conservative sources and the very vocal “cannabis is completely safe” contingent. Despite decades of tracking children and studying cannabis’ effects in lab animals, our understanding of cannabis’ effect on the developing human brain is in its infancy.

Josh Kaplan and Hanna Webster's Bio Image
Josh Kaplan and Hanna Webster

Josh Kaplan, Ph.D., is an Assistant Professor of Behavioral Neuroscience at Western Washington University. He is a passionate science writer, educator, and runs a laboratory that researches cannabis' developmental and therapeutic effects.

Hanna Webster is a Western Washington University graduate in behavioral neuroscience and creative writing. She currently works in Dr. Kaplan’s lab as well as on Northwest Laboratory’s COVID-19 PCR team. She is a published author and a freelance science writer.

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