For some pregnant women, morning sickness isn't just an annoyance; it's severe and unrelenting and can't be relieved even with medications.

Concerned they could become under nourished during this critical time of their baby's development, some pregnant women are turning to an alternative treatment: marijuana.

Used by many cancer patients and those with nausea, marijuana has long been known to increase appetite and reduce vomiting. But is it safe in pregnancy?

Katie, who is 30 weeks pregnant with twins, often stirred a tiny spoonful of marijuana oil into her morning coffee during her first trimester, and says it has helped to stop her relentless morning sickness.

"I can eat. I don't throw up and I can hold down food. So in those very important stages when the babies need to get nutrients, the babies get nutrients," she says.

Katie asked us not to show her face or use her real name. That's because most doctors are adamant that marijuana in any form shouldn't be used during pregnancy. They say it has been linked to premature birth and behavioural issues in children. But Katie says she doesn't smoke the drug, and she drinks only small amounts.

"I am not hurting my babies. I am helping my babies," she told CTV News, adding that it's a growing trend. She said she knows lots of women who used marijuana during their pregnancies, and all their children are fine.

But some researchers aren’t so sure, like Andra Smith, an associate professor at the University of Ottawa's School of Psychology, who did her MRI research at The Royal’s Brain Imaging Centre.

She recently completed a study that shows that brain function is changed in young adults whose mothers smoked marijuana during pregnancy. It didn't affect their IQ, but their brains had to work a bit harder to function, with unknown long-term effects.

"I think this is really important information to get out there, that even if you can have this short-term relief of morning sickness, you might be impacting the future success of your offspring," Smith told CTV News.

Virginia Vidal also used marijuana during her pregnancy. She said she had morning sickness so severe, she contemplated ending her pregnancy with triplets. She tried the standard medications for morning sickness but said they didn't work for her. So she started putting marijuana oil in her tea.

"I just remembered, I had tried it and I felt really good and I was able to eat and I was able to keep the food down," Vidal said, "and that was the only thing that was beneficial to me."

Nine years later, she said her children Marissa, Maya and Miguel don't show any ill effects.

"I say the proof is in their health, in their intelligence. They definitely do not have any behavioural issues," she said.

With many women looking for options to treat nausea in pregnancy, and with marijuana about to become even more widely available in Canada, it's possible that the drug's use during pregnancy will grow.

But until more is known about the drug and its effects on growing babies, doctors urge pregnant women to try more conventional morning sickness treatments first, such as vitamin B6 and ginger, and approved prescription medications.

With a report from CTV medical specialist Avis Favaro and producer Elizabeth St. Philip