Is cannabis safe during preconception, pregnancy and breastfeeding?

Cannabis resource series

Supporting information for health care providers

The Society of Obstetricians and Gynaecologists of Canada recommends that: ^{Footnote 12}

• Pregnant women and women of child-bearing age be asked periodically about substance use, including cannabis.
• Healthcare providers should advise pregnant women to abstain from or reduce cannabis use during pregnancy to prevent negative long-term cognitive and behaviour outcomes for exposed children.

Cannabis use among pregnant individuals

More research is needed to clearly understand all the potential effects of cannabis on fertility, pregnant and breastfeeding women, and their offspring ^{Footnote 1}.
Cannabis is the most frequently used illicit drug during pregnancy ^{Footnote 9}. Although there are no recent Canadian statistics on cannabis use during pregnancy, in a recent (2015) national US survey, approximately 3.5% of pregnant women reported using cannabis during the past month ^{Footnote 13}. Use of cannabis by pregnant women is relatively constant throughout pregnancy: 4.0% of pregnant women use cannabis during their first trimester compared to 3.5% and 2.7% in the second and third trimesters, respectively ^{Footnote 13}.

Effects of cannabis on fertility

Using cannabis may decrease the ability to become pregnant:

• In men, using cannabis may decrease the number and the motility of sperm making it harder to get their partner pregnant ^{Footnote 6}.
• In women, cannabis may harm fertility through different mechanisms such as menstrual cycle disruptions and decreased egg implantation ^{Footnote 14 Footnote 15}. Using cannabis can also decrease the success of an in vitro fertilization procedure ^{Footnote 7}.

Individuals who are trying to get pregnant should be advised to not use cannabis.

Effect of using cannabis while pregnant

Short-term effects on the body:

• damage blood vessels when smoked ^{Footnote 16}
• increase heart rate ^{Footnote 1}
• decrease blood pressure ^{Footnote 17}

The decrease in blood pressure may cause dizziness or fainting which may cause injury to both mother and fetus as a result of a fall. Women who use cannabis during pregnancy may also be at greater risk of anemia ^{Footnote 8}.

Short-term effects on the brain:

• sleepiness and fatigue ^{Footnote 18 Footnote 19}
• confusion and forgetfulness ^{Footnote 18}
• anxiousness and fear of others (paranoia) ^{Footnote 18}
• impaired coordination ^{Footnote 20 Footnote 21}

Effects of cannabis on fetuses and breastfed children

During pregnancy, chemicals found in cannabis, such as THC, the substance that produces the “high” and other effects on the brain and body, are carried through the bloodstream to the fetus ^{Footnote 22}.

Similarly, if cannabis is used while breastfeeding, THC passes from the blood into breastmilk and then on to the baby. There may be up to eight times more THC in breast milk than in a mother’s blood ^{Footnote 23 Footnote 24}.

THC (and other cannabinoids) are stored in fat ^{Footnote 25} and are slowly released from the fat back into the bloodstream ^{Footnote 26}. In heavy users, it can take up to 30 days after stopping cannabis for THC levels to be undetectable in the blood ^{Footnote 27}. This means that even if one has stopped using cannabis, THC and other cannabinoids may still be in the blood and be passed onto the fetus or the breastfeeding baby.

THC that is passed on from mother to baby during pregnancy and breastfeeding can affect a baby’s health in many ways. For example:

• Exposure to cannabis during pregnancy is associated with a low birth weight ^{Footnote 1 Footnote 28}.
• Babies exposed to THC through breastmilk may be drowsy, have reduced muscular tone and have poor suckling ^{Footnote 29}, which could impact breastfeeding success and the baby getting enough breastmilk.

It is possible that the effects may persist depending on the extent and duration of the child’s exposure to cannabis. If cannabis is used during pregnancy or breastfeeding, it may affect a child’s brain development, behaviour and mental health ^{Footnote 30}. The child may have problems remembering things and paying attention in school and experience difficulty thinking through problems. This could affect their behaviour (e.g. make them hyperactive) and even increase the chance they will use cannabis when they are older ^{Footnote 9 Footnote 10}. However, more research is needed to better understand the long-term health effects of cannabis use on fetuses and breastfed babies.

Using cannabis for medical purposes during pregnancy or breastfeeding

The Society of Obstetricians and Gynaecologists of Canada recommends that alternative therapies proven to be safe during preconception, pregnancy and breastfeeding should be recommended over cannabis for medical purposes ^{Footnote 31}.

Using cannabis to treat nausea and vomiting of pregnancy

Some women use cannabis to treat nausea and vomiting during their pregnancy ^{Footnote 32 Footnote 33}. However, this is not a recommended practice ^{Footnote 34}. Women are encouraged to ask their healthcare provider about safer alternatives to treat nausea and vomiting during pregnancy.

Briefs available in this series:

Is cannabis safe to use? Facts for youth aged 13–17 years.
Is cannabis safe to use? Facts for young adults aged 18–25 years.
Does cannabis use increase the risk of developing psychosis or schizophrenia?
Is cannabis addictive?