Cannabis use sending more pregnant Canadians to hospital, new study finds

Researchers behind a new study suggesting an increase in hospital visits by pregnant people related to cannabis use say they’re concerned about the potential risks, including premature births and low birth weights.

Severe morning sickness the biggest risk factor, researcher says

Doctors worried as more people using cannabis during pregnancy

4 months ago
Duration 2:36
A new study suggests nearly twice as many pregnant women are being hospitalized due to cannabis use since pot was legalized in Canada. Though numbers are low, it's still raising concerns.

Researchers behind a new study suggesting an increase in hospital visits by pregnant people related to cannabis use say they're concerned about the potential risks, including premature births and low birth weights.

The research paper, published Monday in the Canadian Medical Association Journal, tracked data from close to one million pregnancies in Ontario between January 2015 and July 2021. 

Someone in a lab coat gives a pregnant person an ultrasound.
A new study shows a small increase in emergency room visits and hospitalizations related to cannabis use by pregnant people. (Serhii Bobyk/Shutterstock)

Of those, a small fraction — 540 pregnant people — visited an emergency room or were hospitalized for cannabis use, according to health administrative data compiled by the researchers. Most of those cases, 390, were emergency room visits.

But the rate of acute care hospital visits rose after cannabis was legalized for recreational use in October 2018, from 11 out of every 100,000 pregnancies to 20 per 100,000, the study says.

The lead author, family physician and public health researcher Dr. Daniel Myran, said that while these incidents are rare, they are also serious, and the rising rate is particularly worrying.

"The concern that I have is, these are very severe presentations, and does the increase in these severe presentations represent a much larger increase in general cannabis use during pregnancy?" he told CBC News.

The study notes the most common reason for needing emergency care related to cannabis was harmful substance use, according to the codes used by hospital staff. That was followed by cannabis dependence or withdrawal, and acute intoxication.

Myran, a fellow at the Bruyère Research Institute and The Ottawa Hospital, said the babies born to these patients were more likely to have lower birth weights, premature births or require admission to a neonatal intensive care unit.

"Given the unknown risks of cannabis at this time, the safest course of action is to not use cannabis during pregnancy," he said.

'We don't have the answers yet'

But other researchers caution that more evidence is needed before making any broad recommendations.

The study suggests the biggest risk factor for cannabis use during pregnancy was severe morning sickness, and Myran said women might be self-medicating to relieve their nausea.

Marlena Fejzo, a researcher at the University of Southern California, pointed out that severe forms of nausea and vomiting can also lead to low birth weights and premature births, making it unclear whether cannabis use or an underlying health condition is responsible for the negative outcomes in the Ontario study.

Fejzo is also the science advisor of the Hyperemesis Education and Research Foundation, a non-profit that focuses on a condition of extreme nausea and persistent vomiting called hyperemesis gravidarum, experienced in about one per cent of pregnancies.

"We don't have the answers yet as to whether it's safer to take cannabis than to leave your hyperemesis untreated in pregnancy," she said.

An extreme closeup shows a person's pink lips holding a smoking cannabis joint.
The most common risk factor for pregnant people who used cannabis was severe morning sickness, according to a new study. (David Donnelly/CBC)

She experienced the debilitating condition during pregnancy, and said she was so sick she was unable to eat or drink.

Her research, conducted in the U.S., shows that many pregnant people have reported using cannabis because other treatments aren't effective for their nausea and vomiting. They say cannabis is the only thing that allows them to eat.

"People are taking cannabis, so you can't just ignore that fact," Fejzo said. "They deserve answers as to the safety of cannabis use in pregnancy."

'Left in the lurch'

Dr. Dominique Morisano, an adjunct professor in public health at the University of Toronto, added that people dealing with mental health concerns during pregnancy may also turn to cannabis to self-medicate.

"A lot of women are left in the lurch during and after pregnancy in terms of their mental health care," she said.

Hormonal swings and the major life changes that can come with a baby can bring new psychological challenges, meanwhile some — but not all — pharmaceutical drugs are off limits during pregnancy and therapy is expensive, Morisano pointed out. 

"We should be doing better for pregnant women and postpartum care in our society," she said.

"If we don't, people are going to look for their own ways to take care of themselves."

According to Health Canada, the safest option is to stop using cannabis during pregnancy. The federal agency recommends that medicinal cannabis users speak to their doctors about safer alternatives.

The Society of Obstetricians and Gynaecologists of Canada says there is strong evidence that cannabis use during pregnancy poses risk of lifelong harm to a developing fetus related to memory function, hyperactive behaviour, anxiety and depression.


Bethany Lindsay


Bethany Lindsay is a Vancouver-based journalist for CBC News. Questions or news tips? Get in touch at or on Twitter through @bethanylindsay.

With files from The Canadian Press