Scientists say they know why pregnant women may reach for a THC gummy or joint.

It can help alleviate symptoms such as body pain, anxiety and morning sickness during pregnancy.

“There are medications that you can be prescribed, obviously, for morning sickness,” John Howland, a professor of pharmacology at the University of Saskatchewan, told CBC. “But some people might choose to use cannabis as an alternative.”

Howland said that he hasn’t conducted an official survey, but that he did have conversations with women about their choices in cannabis usage. 

With cannabis legalized less than a decade ago, there’s a lack of research on how it affects people. That includes use during pregnancy, and how it can affect the child.

That’s what Howland is trying to find out, by exposing pregnant mice to THC smoke. THC is the compound of cannabis that creates the high.

Testing effects on rodents

The prenatal cannabis exposure project is run out of the University of Saskatchewan’s THC lab, using grants from the federal government. The five-year project is currently in its second year.

It involves pregnant mice inhaling THC smoke every day during their month-long pregnancy cycle.

“It’s like a hotbox system,” Howland said. “The animals inhale the air that contains that smoke for 15 minutes and we take them out.”

Once the pregnant mice exposed to THC give birth, Howland and his students study the effects on the offspring. They also compare their behaviours to baby mice whose mothers were not exposed to the smoke.

“Sometimes we test offspring as early as a couple of days after birth and sometimes it’s a couple months,” Howland said. “So a cycle of that would take four to six months to complete the experiment.”

The experiment has revealed that baby mice whose mothers have been exposed to THC smoke have problems.

“I mean, it affects the whole body,” Howland said.

He found the main differences in the offspring were increased anxiety levels, altered decision-making skills and a below-average birth weight.

Howland’s team said anxiety levels are measured through the lab’s maze system. Offspring from the mice exposed to THC sit stagnant in their cage, while the non-exposed offspring freely explore their tunnels as usual.

“They’re going to spend more time in the closed part or hiding in a corner versus exploring an open area,” said Kaelyn Young, a pharmacology masters student helping lead the project. 

“And then in tests that are more of like a conditioned response to fear, they’re going to have more of a freezing reaction than an animal that isn’t displaying those anxiety-like behaviours.”

Decision-making skills are measured through a chamber in the lab with a touch screen, which mice can poke with their noses.

“They learn how to receive a food reward based on touching those images,” Young said. “When we test the animals in that way, they actually are able to switch more quickly and seem to learn the rules more quickly, which we’re not entirely sure why that is.”

Howland has experimented with other types of cannabis, but said THC has the most profound impact.

“It seems that the CBD smoke is less of a factor than the high THC,” Howland said. “We do have a study where we injected higher doses of CBD and saw changes in the offspring, but they were quite subtle.”

Studies from other universities have revealed similar results.

“The size and the rate of development of the brain doesn’t really track,” Mallar Chakravarty, a professor of psychiatry at McGill University, told CBC. “What we see in these mice is that they’re more anxious as they get older, and specifically the female.”

Chakravarty was involved in a rodent study out of the Douglas Research Centre in Montreal. His experiment involved injecting a measured amount of THC into the bloodstream of pregnant rodents and studying the effects on their offspring.

Risks to a child’s brain development

Anick Berard is a professor of pharmacoepidemiology (which blends pharmacology and epidemiology to study the effects of drugs in defined populations) at the University of Montreal. She researches prenatal health by studying how different drugs affect pregnancy. 

She said in her research, about four per cent of women reported using cannabis during the first trimester of pregnancy.

“So if you continue in the second and third trimester, there’s a possibility that it will affect your child’s brain development,” Berard said. “This is where research has shown a link with later anxiety, cognitive problems and children’s hyperactivity.”

Health Canada declined an interview, but provided CBC with information which confirms that cannabis use during pregnancy could result in a newborn being born with lower birth weight and alertness.

Other risks Health Canada points to include:

Age 0-3 years:

• Difficulty calming down.
• Exaggerated startles.
• Sleep problems.

Age 3-6 years:

• Poor memory.
• More impulsive.
• Less attentive.

Age 6-10 years:

• Difficulty learning.
• Symptoms of depression and anxiety.
• Difficulty making decisions.

Age 14-18 years:

• Poorer school performance.
• Delinquency problems.
• May try/use cannabis earlier.

“There’s some data showing an association with hyperactivity,” Berard said. “Less achievements at school, aggressivity, so cognitive function in the bigger sense.”

“There’s some research showing that they are more likely to be addicted to substances. So that could be cannabis, but could also be alcohol and smoking.”

Unlike a condition like fetal alcohol syndrome, there aren’t any exact physical attributes for a child whose mother smoked during the pregnancy.

Health Canada also discourages the use of cannabis while breastfeeding, as these risks could still apply if cannabis is passed to the baby through breast milk.

“The caveat is that we still don’t have enough data,” Berard said. “But the data that we have is not reassuring.”

More addictions resources needed

James MacKillop, who holds a chair in addictions research at McMaster University, told CBC that cannabis is a very addictive substance. He said that a lack of resources for those struggling with cannabis usage makes regulating the addiction difficult.

“It may be individuals who were already struggling with cannabis use disorder before they became pregnant,” Mackillop said.

“One of the challenges in treating cannabis use disorder is [that] we actually don’t have any approved medications or other medical interventions.”

Howland plans on continuing his cannabis research on rodents and has already begun publishing the findings of his experiments online.

Although Howland said he still has more ground to cover in his experiments, he has a clear message to spread about the usage of cannabis products, especially during pregnancy.

“The dosing [of THC products] has gone up dramatically,” Howland said. “And I think people really need to be aware of that.”

“Less is better. That would definitely be one of the key messages.”