Is it safe to use weed during pregnancy?

It’s worth a try, Mallory Pollock* thought as she sat on her couch, lit a joint and tentatively took a few puffs. At eight weeks pregnant, she had already endured three weeks of relentless morning sickness and was desperate for relief. She couldn’t get a good night’s sleep because she was constantly waking up to get sick. Earlier that day, a smell in the grocery store had sent her rushing to the washroom to throw up, and on her way home, she had to pull over to puke again. Her stress level was skyrocketing as she worried that her lack of nutrition and rest may be harming her baby. “It was escalating and every little thing was setting me off,” she says. “It was out of control.”

Pollock had already tried the morning sickness drug, Diclectin, but it didn’t work for her (and research suggests it doesn’t work, period). A daily marijuana smoker before pregnancy, she had quit cold turkey the day she found out she was expecting because she didn’t want to do anything that might be bad for her baby. But smoking pot had helped her manage nausea and digestive problems in the past, and she wondered if it could ease her symptoms this time, too. She had her answer within minutes of inhaling. “It was like instant relief,” she says. “I sat down to a smorgasbord of food. I was like, this is heaven. I’ll never forget that moment.” 

Estimates of how many women use cannabis during pregnancy vary from three to 30 percent, and women of childbearing age are the fastest-growing group of recreational users. It’s hard to know exactly how many women take the drug during pregnancy because many are afraid to report it. When Pollock started smoking a few puffs three times a day, she hardly told anyone, most certainly not her doctor who she feared would report her to child protection services. But many women who smoke weed—about half according to some studies—quit for the duration of their pregnancy.

And with good reason. Some research suggests that using cannabis can lead to poor pregnancy outcomes and have long-term neurodevelopmental effects on the child. Experts are worried that when marijuana is legalized in Canada on October 17, expectant mothers might think it gives them the green light to use.

“We’re really concerned that pregnant women are going to think that just because cannabis is legal, it’s safe,” says Jocelynn Cook, chief scientific officer with the Society of Obstetricians and Gynaecologists of Canada (SOGC). “The science isn’t conclusive, but it does show that there is potential for cannabis to cause harm that could last for a lifetime.”

Why pregnant women use weed

According to one study, more than half of women who used marijuana during pregnancy were, like Pollock, doing so to treat morning sickness—and 92 percent said it worked. While your doctor or midwife is highly unlikely to prescribe cannabis for this purpose—the SOGC strongly discourages any use during pregnancy—the budtender at your local dispensary might. A recent survey of dispensaries in Colorado found that 69 percent recommended using cannabis to treat morning sickness and 36 percent said it was safe during pregnancy despite evidence to the contrary.

Women may also use pot to relieve other pregnancy symptoms, such as sleep disturbances, lack of appetite and aches and pains. Some women will have been using cannabis prior to pregnancy to treat medical conditions—fibromyalgia, depression or anorexia, for example—and keep using out of fear that their symptoms will return if they quit, which can be harmful for them and their babies.

Recreational users could be addicted and think that their habit is harmless. A study published in 2015 found that 70 percent of pregnant women in the United States who used pot in the previous year believed that there was a slight or no risk of harm from using the drug once or twice a week. “Women really want to think that it’s safe to use,” Cooks says. But some research suggests they’re wrong.

What are the risks of using weed during pregnancy?

There are more than 400 active chemicals in cannabis, some of which cross the placenta and enter the baby’s brain and tissue. Most research has focused on tetrahydrocannabinol (THC), the primary psychoactive component of marijuana, and cannabidiol (CBD), the primary non-psychoactive component. After a pregnant woman uses weed, the amount of THC in her baby’s blood is about a third to a tenth of the level in her own blood. And CBD has been found to increase the placenta’s permeability, allowing for THC and other foreign substances to pass into the baby’s blood more easily.

Marijuana affects the functioning of the placenta in other ways, too, such as reducing the flow of blood and oxygen, which may affect infant growth and development. The endocannabinoid system, which mediates the effects of cannabis, is detectible when the baby is just an embryo and plays a key role in early brain development.  Experts say exposure to cannabis at this early stage could affect neurodevelopment. “We know that cannabis isn’t good for the developing teenage brain—the evidence is very strong there—so it can’t be good for the developing fetal brain,” Cook says.

Studying the effects of marijuana exposure on pregnant women and their children is complicated by the fact that women who use cannabis often use tobacco and other drugs, which makes it challenging to tease out the effects of the different substances and results in findings that are often conflicting and inconclusive.

A 2017 report by the Canadian Agency for Drugs and Technologies in Health, a Canadian not-for-profit that provides objective medical evidence, reveals that one systemic review and five studies found an increased risk for adverse outcomes such as preterm birth, stillbirth and admission to the neonatal intensive care unit, while another systematic review and three other studies contradicted these results. The strongest evidence appears to be for low birth weight, which is a key indicator of overall health. A recent meta-analysis found that infants exposed to marijuana weighed about four ounces less, and a study of more than 26,000 births in Ontario found that pregnant women who used marijuana were almost three times more likely to have an infant with low birth weight.

“The evidence is continuing to grow,” says Jamie Seabrook, an associate professor in the School of Food and Nutritional Sciences at Brescia University College and one of the authors of the Ontario study. “Marijuana is being consumed during pregnancy across all levels of education and income, and regardless of socioeconomic status it’s having a huge effect on low birth weight, even after adjusting for tobacco smoking.”

When marijuana-exposed babies are born, they’ve been found to have increased tremors, exaggerated startle reflexes, high-pitched cries, abnormal sleep patterns and other behaviours that researchers have likened to opioid withdrawal.

Maternal marijuana use also appears to have subtle effects on neurodevelopment. Two longitudinal studies found that by age three to four, children exposed to heavy cannabis use (one or more joints per day) have deficits in memory, verbal skills and visual and verbal reasoning, and are hyperactive and have difficulty paying attention. A third longitudinal study, however, did not find evidence of these effects, but it did note increased aggression and attention problems as early as 18 months.

By age nine to 10, two of these same studies found that exposed children have deficits in reading, spelling and executive functioning (the set of skills responsible for attention and self-regulation). One found that by age 14, the kids did significantly worse in school and were nearly twice as likely to display delinquent behaviour. There is also growing evidence that prenatal exposure to cannabis leads to higher rates of mental illness in childhood and substance abuse in adolescence.

“The effects probably aren’t huge from what we can see now, but it doesn’t mean that they’re not going to impact somebody’s life in a negative way,” Cook says.

Using marijuana during pregnancy can also negatively affect the mother, raising the risk for anemia, and increasing heart rate and decreasing blood pressure, which may cause dizziness and fainting. When women are high, they may have impaired coordination, adding to the clumsiness that comes with pregnancy, and become confused and forgetful, exacerbating baby brain. Pregnancy is a high-risk time for mental illness, and using pot can lead to paranoia and bring other psychological issues to the surface.

Are edibles and vaping safer during pregnancy?

Many women try to mitigate harm by changing how they use weed and cutting back on how much they consume. Pollock, for instance, smoked less than she did before she was pregnant—one joint would last her a few days—and tried a vape but went back to smoking because it didn’t have the same effect. Vaping reduces exposure to the byproducts of combustion and the carcinogens in marijuana smoke but, like with smoking, the THC still transfers almost immediately into the bloodstream. Edibles, tinctures and lotions don’t have the harmful effects of smoking, and they lead to lower levels of THC in the mother’s blood. Still, no method of delivery—vaping, smoking or ingesting—has been proven to be safe. “No matter what way it’s ingested, the active ingredients in cannabis are still getting into mom’s bloodstream and still being passed on to the fetus,” Cook says.

Studies have shown that the more cannabis a woman consumes, the greater the risk to her baby, but “we don’t know how much is absolutely safe and we don’t know how much is absolutely harmful,” Cook says, adding that we probably never will, since four decades of research into alcohol use during pregnancy have yet to determine a safe limit. Pot is also getting more potent. A study of more than 38,000 samples found that THC levels tripled in two decades, from four percent in 1995 to 12 percent in 2014.

How to stop using weed during pregnancy

Cook advises women who are using cannabis to talk to their healthcare providers about alternatives that have been proven safe during pregnancy. Women who are using the drug for a medical reason can explore other treatments, such as cognitive behavioural therapy or antidepressants for anxiety and depression. Those hit by morning sickness can try vitamin B6, an antihistamine or an anti-nausea medication such as Gravol.

Women who decide to stop using marijuana may have to wait several weeks for the drug to clear their system. THC and other cannabinoids are stored in fat and slowly released into the bloodstream, and it can take up to 30 days for THC to leave the blood of a heavy user.

And for those who remain unconvinced based on the limited existing evidence, there’s good news: In January, the federal government announced $1.4 million in funding for marijuana research, and exploring the effects of use during pregnancy is a priority area. “Women deserve to know the evidence,” Cook says. “It’s not enough to say, ‘Don’t do it.’”

Whether women will one day be popping pot pills for morning sickness or seeing warning labels against use during pregnancy remains to be seen. But for now, it’s safest to avoid the drug.

*Name has been changed.

Listen to Today's Parent editor-in-chief Kim Shiffman talk about pot on The Big Story podcast.

The Big Story, October 16

Learn more at The Big Story Podcast.

Read more: How to tell your kids you smoke weed The real dangers of drinking while pregnant