Using cannabis while pregnant can affect placenta, stress, anxiety, development in children: study

Cannabis use during pregnancy to relieve nausea, stress, and anxiety has climbed over the past two decades, but a new study suggests children who were exposed while in utero showed higher levels of a stress hormone, anxiety, aggression, and hyperactivity. In addition, tests on the placenta indicated genetic changes linked to immune function.

The peer-reviewed study, published in Proceedings of the National Academy of Science (PNAS), is the latest study to suggest a negative growth and health impact on children from cannabis use during pregnancy. Researchers say the developing brain is sensitive and vulnerable and the drug — which contains more than 700 chemical compounds — can hijack that development.

“I’m just worried that in our society today, when we say that cannabis is completely fine for everybody, it’s not,” Yasmin Hurd, Director of the Addiction Institute at Mount Sinai in New York, and senior author of the paper, told CTV News. 

The study notes that along with the softening public view towards marijuana, it has become the most consumed recreational drug during pregnancy, with those saying they have used cannabis in the past month ranging from three to 16 per cent.

“We need to at least educate people and educate women and their doctors so that they can make the decision and so that also we can be able to help children early, not to wait so very long … that to me is also very critical.”

One 2020 study found that children with prenatal exposure were more likely to have psychotic-like behaviours, weaker cognitive abnormalities, and greater social, sleep, and attention problems.

Another large study last year, led by researchers at The Ottawa Hospital, found evidence suggesting children with exposure during pregnancy had an increased risk of being diagnosed with autism. The same research team had previously reported that it also heightened the risk of early labour. It has also been linked to low birth weight.

Health Canada recommends avoiding using cannabis when pregnant and breastfeeding, or to treat morning sickness or for other medical purposes.

“The more cannabis is taken during pregnancy, the more it affects the baby’s developing brain,” the agency says on its website, which also outlines some of the different developmental risks for children at different ages.

“There is no known safe amount of cannabis use during pregnancy…although cannabis is a natural plant, it doesn’t make it safe during pregnancy.”

The latest paper, led by researchers with the Icahn School of Medicine at Mount Sinai and City University of New York, tracked 322 individuals, 71 of whom reported using marijuana during their pregnancy and/or while breastfeeding. Scientists collected the placenta after birth and followed up with their children when they were around three to six years old.

Hair samples from the children found higher levels of the cortisol stress hormone, and a heart rate variability (HRV) test found a decrease in normalized HRV. This normally happens during stress and is viewed as a marker of the autonomic nervous system function and sensitivity to stress. Elevated levels of anxiety, aggression and hyperactivity were also recorded in the young children, the study found.

The placenta of some of the children with behavioural assessments were processed for RNA sequencing, with scientists finding that cannabis use while pregnant lowered the expression of immune-activating genes, including immune system markers that would normally help protect the body against pathogens.

“Using gene coexpression analysis, we revealed immune-related gene networks in placenta significantly correlated with anxiety problems and hyperactivity,” the authors wrote.

“In line with previous investigations reporting greater risk for psychiatric illness in … children with prenatal cannabis exposure, the current study showed that [maternal cannabis use] is associated with increased anxiety, aggression, and hyperactivity in young children. Moreover, along with several altered psychobehavioral traits, [these] children exhibited endocrine and physiological phenotypes consistent with aberrant stress and anxiety regulation.


For Jordana Zabitsky, a mother of two young children, aged four and almost six, cannabis helped relieve many of her mental health issues during her pregnancy.

“I did use cannabis during my pregnancies with both because I suffered severely from mental health issues like depression, chronic anxiety, PTSD, panic disorder and [premenstrual dysphoric disorder],” she told CTV News.

The cannabis helped her come off more than 350 milligrams of pharmaceuticals prior to becoming pregnant, she said, saying she felt a lot safer using it during her pregnancies than continuing with medication like Seroquel, an antipsychotic drug used to treat illnesses like bipolar disorder and major depressive disorder.

During her first pregnancy with her son, Zabitsky was reluctant to use too much and consumed only a “very, very small amount,” she said.

But when she was pregnant with her daughter, she used cannabis more regularly, which made the pregnancy a lot easier, she said.

“I also had on top of my mental health, my pre-existing mental health conditions. With my pregnancy, I also had … prenatal anxiety, prenatal depression, prenatal rage, which was caused by my general mental health issues prior to becoming pregnant.”

Zabitsky also experienced pubis dysfunction with both her pregnancies, a condition where the pelvic joints become either stiff or move unevenly, and can be debilitatingly painful.

“Mine happened at 16 weeks with my son and then 18 weeks with my daughter, so I couldn’t stand up without pain, walk, sit down, roll over in bed without excruciating pain. If I went out I had a pillow with me. if I went to the mall I had a wheelchair. It was brutal,” she said.

“Cannabis has helped with my mental health in many different aspects. It allowed me to feel a lot less anxious. It cleared most symptoms of depression, and it definitely helps ease the pain.”

Her children, she says, have “developed beautifully and hit every single milestone and then some.”

Zabitsky, who operates an online business called Mothers Mary that offers maternal mental health care services and support during and after pregnancy, says it is important to note that consuming cannabis during pregnancy is not done lightly or to “get high.” And with other medication being unsafe or not working, many parents wonder, what are their options when they are pregnant?

“They’re using it with the intention to decrease their pharmaceutical use, to have pain free options, to not use pharmaceuticals … antipsychotic medications, or even any sort of mental health pharmaceutical,” Zabitsky said.


With the growing evidence that marijuana use during pregnancy can be potentially detrimental to the child’s health, however, health organizations are looking to spread the word about the risks, and putting out public service announcements including educational videos.

“With alcohol, there’s quite prominent warnings on packaging to avoid use while pregnant, and I think something similar for cannabis is needed now just given the number of studies that have shown potential risks for pregnancy outcomes and for later child development outcomes,” says Daniel Corsi, a scientist with the Children’s Hospital of Eastern Ontario (CHEO) Research Institute.

The latest study noted that gestational development is highly vulnerable to environmental factors introduced through the placenta. THC (tetrahydrocannabinol), the main psychoactive compound in marijuana, passes easily from maternal blood to the fetus via the placenta. At the same time, the study noted that the concentration of THC has increased over the last 10 years, heightening its potential harm.

“I’m concerned because women are being targeted to increase their cannabis use,” says study co-author Hurd.

“And we need to have early interventions and be able to help children. And women shouldn’t be stigmatized. Women shouldn’t be targeted.”