Is Cannabis Safe During Pregnancy & Breastfeeding?

Some new and expecting moms perceive cannabis and CBD as safe and natural remedies for pregnancy and postpartum ailments. But science doesn’t back that up.

Since the 2014 legalization of recreational cannabis in Oregon, pot has become a commonplace part of Portland’s landscape (on sunny days, it can feel like its’ scent permeates the entire city’s air). Yelp lists more marijuana dispensaries than brewpubs in the metro area, and that’s not counting the coffee shops offering shots of CBD in your chai latte.

So yes, those cannabis products are everywhere, accompanied by claims that they’ll alleviate many of the maladies familiar to pregnant and postpartum women, like nausea, anxiety and insomnia. But is it safe to use when you’re growing a new person in your uterus, or breastfeeding one?


The American College of Obstetricians and Gynecologists, American Academy of Pediatrics, and the Academy of Breastfeeding Medicine all strongly discourage cannabis use in pregnant and breastfeeding mothers, citing worrisome data about effects on fetal growth and brain development.

Yet, local mothers are surrounded with conflicting information about this topic. Blogs and social media groups promote the benefits of cannabis in pregnancy, even advertising meetups for Portland mothers who want to learn more. Dispensaries may also be encouraging its use; a 2018 study from Colorado found 69 percent of contacted dispensaries recommended cannabis products to treat morning sickness. Nationally, studies show that more women are using cannabis in pregnancy as more states legalize it.

Shauna O’Neal, certified nurse midwife and family nurse practitioner at Women’s Healthcare Associates in Tualatin, said that people may perceive cannabis as safe for a variety of reasons. “The fact that it’s legal and the fact that it’s a plant contribute to this perception of safety, because it’s natural.” But, she points out, “tobacco is also natural, is also legal, and it’s also definitely not recommended in pregnancy.”

Cannabis Safety in Pregnancy

To judge the safety of any substance, natural or otherwise, it helps to understand the chemical molecules within it and how they react in the body. Cannabis contains at least 500 different chemical compounds, more than 100 of them considered cannabinoids.


The main psychoactive molecule is delta-9-tetrahydrocannabinol, otherwise known as THC and the focus of most cannabis research. THC is a small, fat-soluble molecule that easily crosses the placenta and enters breast milk, and once in the bloodstream of a fetus or baby, likely accumulates in fat-rich tissues like the brain and adipose tissue. (While there’s a lot of hype and hope about the medicinal properties of cannabidiol, or CBD, there’s virtually no research on its effects in pregnancy or breastfeeding.)

Research on how THC affects developing humans is challenging, and results have sometimes been conflicting. Most studies are observational, tracking outcomes in babies and kids whose mothers reported using marijuana in pregnancy, but their lives are often complicated by other factors, like alcohol and tobacco use, abuse and trauma.

Researchers try to sort out these confounding factors, but there is uncertainty about whether observed effects are directly caused by cannabis. Still, some concerning and consistent themes emerge in these studies. “We don’t have great safety data on it,” O’Neal said, but “what we do know is not reassuring.”

Fetal development is an intricate, complex process, and many people don’t realize that it’s in part orchestrated by natural cannabinoid molecules made in the body. When THC and other molecules from cannabis cross the placenta, they can potentially hijack normal development. While cannabis use in pregnancy doesn’t seem to cause any obvious birth defects, there is evidence that it might interfere with fetal growth and development of brain circuitry, with possible long-term implications.

For example, an analysis published in the medical journal BMJ Open in 2016 combined 24 studies and concluded that babies exposed to marijuana during pregnancy are more likely to have low birthweight or need NICU care. Importantly, much of this research is several decades old, and plant breeding has increased THC concentrations from 1 to 5 percent in the 1960s to 15 to 25 percent and higher in modern cannabis. In other words, yesterday’s research may underestimate the effects of today’s cannabis.

Other research has looked at more long-term effects on brain function. Studies from Canada, the United States and the Netherlands have tracked thousands of children exposed to cannabis in pregnancy. Together, they found little difference in toddlers or preschoolers, but by school age, cannabis-exposed kids were more likely to have problems with attention, impulse control and hyperactivity. In adolescence and early adulthood, they had higher rates of depression and psychosis and were more likely to be using marijuana and tobacco, with greater rates of addiction. Again, separating correlation from causation is tricky in this research,  and these effects haven’t been seen in all studies. For example, a study conducted in Jamaica in the 1980s found no adverse effects of cannabis use in pregnancy in a group of 24 babies assessed through age 4 or 5, so it’s often held up as reassuring evidence of cannabis safety. However, the Jamaica study was small and didn’t assess children beyond preschool, and considering the many studies that have found worrisome effects, most researchers agree that there is a serious risk that cannabis use in pregnancy could affect children in both the short- and long-term.

“You’re not just considering ‘what does this mean for my baby?’ but ‘what does this mean for my teen, in like a decade and a half?’” said O’Neal. And while we need more studies, the existing research suggests cannabis use in pregnancy could have long-term ramifications to our kids.

Cannabis in Breastfeeding

If there’s uncertainty about effects of cannabis in pregnancy, even less is known about its use during breastfeeding. One of the few studies was published in 1990 by Susan J. Astley Hemmingway, Ph.D., now a professor of epidemiology and pediatrics at the University of Washington. She compared 68 1-year-olds who had been breastfed by cannabis users to a control group whose mothers hadn’t used cannabis, but were similar in other factors, including tobacco and alcohol use. At one year, those exposed to cannabis at least 15 days out of the month had significantly delayed motor skills — they were behind in things like stacking blocks, crawling and walking.

Astley Hemmingway said the difference in motor development may not be obvious to a parent, but it was significant enough to be noticeable to a pediatrician, and it would qualify a baby for early intervention services. In addition, most of the participating babies were breastfed for just three months, so they would have had a much lower cumulative THC dose than a baby breastfed for a year or more with today’s potent cannabis. “For a single study, it’s incredibly concerning and compelling that we found statistically significant impacts on motor development,” she said. “It absolutely begs for follow-up studies.” But Astley Hemmingway has since focused her career on fetal alcohol syndrome, and unfortunately, there haven’t been more studies of how cannabis use in breastfeeding mothers affects their babies.

However, studies do show that THC passes into breast milk and remains detectable for somewhere between six days and six weeks after cannabis use. There’s no research on how babies metabolize cannabinoids or how long they stay in a baby’s body. We also don’t know how breast milk cannabinoid levels are affected by different routes of use (inhaled, edible, topical, etc.) or type of product (high-THC or high-CBD). We do know that CBD passes into breast milk, but it will take time for researchers to catch up with all of these relatively new cannabis products.

While we wait for better science, we know enough to assume that exposure to THC — both in pregnancy and through breast milk — “is likely not good for the developing human brain,” said Ilse Larson, M.D., associate professor of pediatrics at OHSU Doernbecher, medical director of the OHSU Mother Baby Unit, and a certified lactation consultant. She firmly recommends that breastfeeding mothers avoid cannabis use.

Weighing Risks, Benefits and Uncertainty

Portland mothers told PDX Parent that the decision to use cannabis while pregnant or breastfeeding wasn’t taken lightly. Irene of Sherwood (she asked that her real name not be used), age 32 and mother of two, was hospitalized because of dehydration from severe nausea and vomiting in her last pregnancy. In her current pregnancy, she’s finding cannabis helps her keep food down. Lindsey Webb, age 40 and mother of two kids, now living in Florida but formerly of Beaverton, used cannabis while breastfeeding her daughter to wean herself off opioid pain medications, which were prescribed after a back injury sustained during childbirth. To her, cannabis felt like the safer choice. In general, medication use during pregnancy and breastfeeding has been under-researched, and women like Lindsey and Irene are making decisions with limited information and imperfect choices.

How women weigh these risks and benefits is a focus of the research of Celestina Barbosa-Leiker, Ph.D., associate dean for research in the College of Nursing at Washington State University. In one yet-to-be-published study, she and colleagues interviewed 20 pregnant women reporting daily cannabis use. All said they were using it for medicinal purposes, to help alleviate symptoms like nausea, pain, or anxiety, or to help them sleep. “They probably don’t want to be using anything, but they’re trying to make that decision,” said Barbosa-Leiker. And the women they interviewed said they wanted to know more about the safety of cannabis. “They’re concerned and they want scientific information,” said Barbosa-Leiker. “They want to make the best decisions possible for themselves and for their baby.”

But both Dr. Larson and nurse-midwife O’Neal emphasized that there are safer alternatives for treating pregnancy and postpartum symptoms, with more evidence and better safety data, compared with the concerning research and unknowns about cannabis.

To Astley Hemmingway, the confusion about cannabis use feels familiar. When she started her career in the 1980s, most people, even many doctors, didn’t know alcohol should be avoided in pregnancy. Only after decades of public health campaigns is it now common knowledge. “It took a long time, but we’re there, and here we go again with marijuana now,” she said. “I know there’s a lot of well-meaning women out there that aren’t drug addicts or anything, but do use legal marijuana, and they’re going to be, I presume, most upset to find out after the fact that they probably shouldn’t be smoking while breastfeeding. Were they appropriately informed so they could make that decision? I think we’re really playing catch-up here.”

Using Cannabis Responsibly

The risks of cannabis to kids go beyond exposure in pregnancy or through breast milk. If you choose to use it, follow these tips to keep kids safe:

» Be sure there’s an unimpaired adult to care for the kids. “Parental intoxication from any substance affects parenting and can compromise the safety of infants and children in their care,” said OHSU pediatrician Dr. Ilse Larson.

» Don’t smoke inside or in the presence of babies or children. Just like tobacco, marijuana smoke contains toxins and carcinogens. Second- or even third-hand smoke (lingering in homes or on clothing) of any kind increases the risk of SIDS.

» Store cannabis products locked and out-of-reach of kids. “Edibles in particular are often appealing in appearance and taste to toddlers and children, but are extremely dangerous; toxic doses can be fatal,” Dr. Larson said

Managing Pregnancy Nausea

Nausea and vomiting are common pregnancy symptoms, but cannabis isn’t recommended as a treatment. Try these tips instead:

» Eat frequent, small meals containing protein and avoiding spicy and fatty foods

» Stay hydrated

» Try ginger candy, tea, or supplements

» If a prenatal vitamin worsens your symptoms, talk to your healthcare provider about switching to a simple folic acid supplement

» If symptoms persist, talk with your provider about medications that can help. There are safe and effective options, with far more research behind them and a better safety profile than cannabis.

Source: American College of Obstetricians and Gynecologists

Further Reading

1. ACOG Committee Opinion: Marijuana Use During Pregnancy and Lactation. Obstetrics and Gynecology, (2017).

2. Astley, S. J. & Little, R. E. Maternal marijuana use during lactation and infant development at one year. Neurotoxicology and Teratology, (1990)

3. Baker, T. et al. Transfer of Inhaled Cannabis Into Human Breast Milk: Obstetrics & Gynecology, (2018).

4. Bertrand, K. A., et al. Marijuana Use by Breastfeeding Mothers and Cannabinoid Concentrations in Breast Milk., (2018).

5. Dickson, B. et al. Recommendations From Cannabis Dispensaries About First-Trimester Cannabis Use: Obstetrics & Gynecology, (2018).

6. Gunn, J. K. L. et al. Prenatal exposure to cannabis and maternal and child health outcomes: a systematic review and meta-analysis. BMJ Open, (2016).

Alice Callahan, Ph.D., is the author of The Science of Mom: A Research-Based Guide to Your Baby’s First Year, and her writing on health and science has been published in the New York Times, the Washington Post and elsewhere. She lives with her husband and two kids in Eugene, where cannabis dispensaries are also everywhere.

Alice Callahan, PhD
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