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Marijuana Use in Pregnancy
Kelsey McLaughlin, PhD

Marijuana is formally legal in Canada, as of October 2018. Statistics Canada has reported that 8% of Canadian females over the age of 15 used marijuana in the last year. Importantly, almost half ot female marijuana users continue to use marijuana while pregnant. 

There has been some discussion whether cannabis therapies could be used by pregnant women who suffer from nausea and vomiting in pregnancy, also known as 'morning sickness'. Could marijuana be a novel therapy available to pregnant women?

Let's talk about nausea and vomiting of pregnancy


Approximately 50-90% of pregnant women experience morning sickness. Most pregnant women with morning sickness experience symptoms during the first month of pregnancy, typically with the worst symptoms at 9 weeks' gestation. 90% of pregnant women with morning sickness start to feel better by 20 weeks of gestation. 

Hyperemesis gravidarum is the clinical term for severe nausea and vomiting; women with hyperemesis gravidarum have intense vomiting, weight loss and dehydration that can require hospitalization.

Scientists think that nausea and vomiting in pregnancy may be caused by the developing placenta. Increased levels of the hormones released by the placenta, including human chorionic gonadatropin (hCG), estrogen, progesterone and prostaglandin E2, have been associated with morning sickness.  Low levels of vitamin B may also contribute to nausea and vomiting in pregnancy.


Interested in learning more about morning sickness? The New York Times has a recent article that discusses recent research into the causes and treatments of nausea and vomiting in pregnancy.

Pregnant women with morning sickness are recommended to avoid specific foods, smells and supplements that may trigger symptoms. 'Alternative' therapies (ie. not medication) may help to control nausea and vomiting for pregnant women, including ginger supplements, acupuncture and acupressure.


Approximately 10% of pregnant women with nausea and vomiting in pregnancy require medication to control symptoms. The first line therapy typically recommended is pyridoxine monotherapy or doxylamine/pyridoxine combination (under the brand name Diclectin® in Canada). 

Ginger, Lemon & Honey Tea

Marijuana as a therapy to prevent morning sickness

Marijuana contains the compound cannabinoids, which are known to prevent nausea and vomiting at certain doses. The American Cancer Society states that a few small studies have shown marijuana to be helpful for treating nausea and vomiting in patients undergoing chemotherapy.


A recent study found that approximately 5% of pregnant women smoked marijuana. Pregnant women with morning sickness used marijuana more frequently compared to pregnant women without nausea. This suggests that pregnant women suffering from morning sickness may using marijuana as a therapy for symptom relief.

Is marijuana safe for use during pregnancy?


70% of pregnant women believe that there is 'slight or no risk of harm from using marijuana once or twice a week'.

Tetrahydrocannabinol (THC) is the main psychoactive component of cannabis. THC can cross the placenta into the fetal blood stream. Animal models have shown that fetal blood levels of THC were 10% the levels of THC in the mother's blood; the levels of THC in the fetal blood were even higher after repeated exposure. This is a high level of THC exposure for their little circulation systems.

THC can also accumulate in breast milk. A recent study reported that THC was detectable in most breast milk samples, even 6 days following the mother's marijuana use. 

Marijuana has significant negative effects on pregnancy outcomeneonatal and long-term neurobehavioural effects. It can lead to lower birthweight of the baby, lower reading comprehension and underachievement, and poor attention span

A Toddler and a Baby

It doesn't sound like marijuana has a promising future for pregnant women...


There is currently no evidence showing that cannabis is effective to prevent symptoms of morning sickness in pregnant women.

The Society of Obstetricians and Gynaecologists of Canada and The American College of Obstetricians and Gynaecologists recommend against cannabis use during pregnancy and while breastfeeding. 


As stated by The Society of Obstetricians and Gynaecologists of Canada, 'Legal Doesn’t Mean Safe'.



Despite marijuana being legal in Canada, pregnant women are recommended to discontinue marijuana use while pregnant. Marijuana use can have negative effects on the baby during pregnancy, as well as the child's long-term learning ability and attention span.


Every woman and every pregnancy is unique. Pregnant women should speak to their healthcare provider to ensure maternal and fetal safety. This article is meant to provide readers with current information and opinions. All medical and treatment decisions should be discussed with your healthcare provider.

This article was written by Dr. Kelsey McLaughlin and edited by Dr. Melanie Audette.

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