Cannabis use in pregnancy and breastfeeding has become more common in Canada despite research suggesting a negative impact on fetal health outcomes. Still, very little is known about why pregnant and lactating people use cannabis, how they decide to use it, and how prenatal and postpartum health care providers can better support and advise patients around this topic.
The cannabis use during pregnancy and lactation project will be done in three phases and will look at:
Funding: Canadian Institutes of Health Research, McMaster University Department of Family Medicine
Pregnancy:
There are not a lot of high quality scientific studies to tell us exactly what will happen when cannabis is consumed during human pregnancy. The available evidence suggests cannabis use during pregnancy may cause complications such as low birth weight, babies being born too early (pre-term birth) and have some impact on development during childhood (1-3). Kids who were exposed to cannabis before birth had issues with things like paying attention, being hyperactive, and acting impulsively during their early childhood (4, 5).
While there is not a lot of good quality clinical evidence in humans, there is a lot of research about how some parts of cannabis affect human cells or pregnancy in mice or other animals. Typically these studies haven’t researched the whole cannabis flower, but instead study different components of cannabis. These studies suggest that cannabis can impact fetal growth or cause low birth weight (6, 7). They also suggest that cannabis can impair the development and functioning of the placenta, which is a very important organ for fetal development and growth (6, 8, 9).
If you can stop using cannabis when pregnant, that is the safest thing for your baby.
Maternal risks of using cannabis during pregnancy are not well-studied. Mostly, what we know is that the risks of consuming cannabis are the same whether you are pregnant or not. These risks include changes in thinking and memory, addiction, problems with your breathing and heart, as well as mental health issues like schizophrenia and mood disorders (10-14). There is one study showing an additional risk of consuming cannabis while you are pregnant – you are more likely to experience anemia, which means low levels of iron in your blood (1). There is some evidence that if you are anemic when pregnant, the baby’s brain development is affected. This may increase the risk that child will have autism, attention deficit/hyperactivity disorder (ADHD) or intellectual disability.(15, 16)
The short answer is no, CBD is likely to be a part of cannabis which causes health problems, even though it doesn’t make you feel high.
Cannabis is comprised of many different chemicals called cannabinoids, but two commonly known ones are THC and CBD. THC is the part of cannabis that can make you feel high, while CBD doesn’t have this effect and is considered “non-psychoactive”- that means that your mind and consciousness feel the same as usual after you consume it.
There have been no clinical studies in humans looking at the safety of CBD during pregnancy. Limited research suggests that CBD may potentially pass through the placental barrier if used during pregnancy. (17) Research on placental cells in humans and on mice shows us that CBD can have negative effects on fetal and placental development (18, 19). This helps us know that even though it doesn’t make you feel high, CBD is still disrupting normal pregnancy development.
Although cannabis is derived from a natural plant, there is not enough evidence to suggest that it is safe to use during pregnancy, and actually quite a bit of evidence to suggest it is not safe (see question 1 and 2). Opium and arsenic are also plant-based substances, and they are not safe to consume in pregnancy.
While pharmaceutical drugs may feel more risky to some people because they are made in laboratories, many drugs prescribed during pregnancy are known to be safe. They are tested through rigorous studies that carefully measure what happens to people who are using these substances. This level of evidence doesn’t exist about cannabis, and so it is not possible to make clear conclusions about the safety of cannabis in the way that it is for other drugs frequently prescribed in pregnancy, like pyridoxine or doxylamine drugs (e.g. Diclectin), which we know to be safe from decades of well-designed scientific studies. (20, 21)
There is currently no evidence to suggest the safety of changing the amount, form, or strain of cannabis for use during pregnancy or breastfeeding. Hopefully in the future, evidence to support these kinds of harm reduction strategies will be available, but right now it is just not possible to say what is safer or riskier.
Because we know that cannabis affects developing brains and other parts of the body, it is safest to minimize your exposure to cannabis during pregnancy and lactation.
Public Safety Canada recommends that if you are using cannabis seek it from an authorized retailer/dispensary to avoid contamination of pesticides, lead, or other substances. (22) Some public health units in Canada have released warnings that they have found cannabis laced with fentanyl, a very strong opioid which can cause a lot of harm and even death in a very small amount (23). These accounts have not been verified, but getting your cannabis from a regulated store/dispensary could reduce the chance that it might be contaminated with any substance.
Health care providers are used to these kinds of questions and their role is to help you have a healthy pregnancy. You might be afraid that they will judge you, and these are valid feelings, but many healthcare providers are used to these kinds of questions and will be glad that you are seeking information to make a decision for the health of your pregnancy.
If you are nervous about bringing this question up with your health care provider, you could use a hypothetical example. For instance, you could say, “I’m thinking about using cannabis during pregnancy to help with my feelings of nausea and vomiting (or whatever reason you want to use it). What do you know about cannabis use during pregnancy that could help me make this decision?” This type of question will help them understand why you are interested in cannabis use, and they can explore that topic with you, including the safety of cannabis for that purpose and other alternatives known to be safe.
Alternatively, you can ask about the potential consequences of using cannabis during pregnancy in a hypothetical scenario to gauge your healthcare provider’s response. You could use wording like “I’ve heard that some people use cannabis when pregnant to help with their anxiety. What would you recommend for someone who is feeling anxious while pregnant?”
We cannot say for sure what your healthcare provider will do, but research and review of guidelines and regulations suggest that clinicians will not call children’s aid society for cannabis use during pregnancy, if that is the only concern that they have.
In a recent study where healthcare providers were interviewed about calling Children’s Aid Society (CAS) or child protective services if a pregnant patient was consuming cannabis, the health care providers described that they would only call CAS if the patient’s cannabis use posed a direct risk to the safety of the child. For example, if the patient was neglecting her children in order to buy and consume cannabis. One doctor in the study compared smoking cannabis during pregnancy to smoking cigarettes. The evidence suggests that both substances have negative health effects, but he wouldn’t call CAS for either one.
There are no Canadian guidelines which suggest that clinicians should report people who use cannabis while pregnant or breastfeeding.
Breastfeeding:
There have been very few studies that have looked at the risks of cannabis exposure through breastfeeding- even fewer than in pregnancy! We do know that cannabis (THC and CBD) passes through the breastmilk to the baby, and that cannabis can stay active in the breastmilk from 6 days to 6 weeks (24, 25). Limited evidence has conflicting results on the impact of cannabis on infant motor development, with some showing that babies exposed to cannabis through breastmilk have slower development of physical motor skills and another study showing no effect (26, 27). Other research shows that cannabis could potentially alter the content of breastmilk by decreasing immunoglobulins and increasing lactose, which means that the baby gets less of the good stuff from the breastmilk. (28)
Cannabis reaches its highest level of effect for the user within the first hour after consuming. However, it takes roughly 25 to 36 hours for half of its activity and potency to diminish, meaning that half of the cannabis will remain in your body during this time. (29) As cannabis will still remain in your body, it may impact the baby if you breastfeed even a few days after consuming cannabis. That said, the concentration of THC in breastmilk does diminish as time passes, so if you are going to breastfeed after consuming cannabis, the longer you can wait the less will be transferred to your baby.
This is a question only you can answer. There are many benefits of breastfeeding for both you and your infant, particularly during the first 6 months of life. It improves the baby’s brain development, reduces risks of obesity for both mom and baby, and also reduces risk of diabetes, high blood pressure, and even some kinds of cancer (30). There is also evidence that breastfeeding can help protect against stress and postpartum depression (31). For babies, it can enhance lifetime immunity (32-34).
As described above, while we know that cannabis is transferred through breastmilk for as long as 6 weeks after the mother consumes cannabis, there is not a lot of clear evidence on what that means for the baby. It is reasonable to conclude that there are negative effects on the baby’s developing brain, but there are so many positive effects of breastfeeding that it is difficult to decide to stop breastfeeding in order to resume cannabis consumption. Some have advised that while it is best to not consume cannabis while breastfeeding, the next best thing to do is reduce your cannabis use while continuing breastfeeding and wait as long as possible after consuming cannabis to feed (27).
We cannot say for sure what your healthcare provider will do, but research and review of guidelines and regulations suggest that clinicians will not call children’s aid society for cannabis use while breastfeeding, if that is the only concern that they have.
In a recent study where healthcare providers were interviewed about calling Children’s Aid Society (CAS) or child protective services if a pregnant patient was consuming cannabis, the health care providers described that they would only call CAS if the patient’s cannabis use posed a direct risk to the safety of the child. For example, if children or infants experienced neglect as a result of their parent consuming cannabis.
Access references for this FAQ here: Vanstone – CanPreg- FAQ Patients -References
There is limited clinical evidence that discusses the outcomes of contemporary cannabis use during pregnancy and while breastfeeding.
In our recent study, pregnant and lactating patients who considered using cannabis sought information from many sources. However, they were relatively unlikely to talk with their clinician about their cannabis use because they are worried about stigma, and/or increasing the likelihood of being reported to child protective services.
Here are some of the most frequent questions we heard from patients about cannabis use during pregnancy or lactation, with brief responses. You may also wish to refer patients to our patient-facing knowledge resource, Cannabis during pregnancy or breastfeeding: Frequently Asked Questions, in the tab above.
As a clinician, you could raise this question with your patients to remove some of that stigma, perhaps using language like “many people wonder if it is ok to keep using cannabis now that they are pregnant. Some people find it very helpful to manage certain conditions or symptoms. Is this something you would like to discuss?”
Making clear to your patients what your reporting obligations are may help them feel more comfortable discussing this topic, or asking questions about their own circumstances or concerns. You could use language like: “Some patients are thinking about consuming cannabis while they are pregnant, but they don’t want to talk about it with their doctor in case that person decides to report them to Children’s Aid Society. I want you to know that I am open to talking about this with you, and that simply knowing you are thinking about using cannabis would not make me consider calling CAS unless there were other factors at play, such as the child being neglected as a result of their parent consuming cannabis”
Additionally, below are some resources that can be used to guide your harm reduction information and may be used to guide your patients.
Access references for this FAQ here: CanPreg – FAQ – Clinicians – V2.0 – References
In this phase, we conducted two systematic reviews. The first describes the perspectives, experiences and information needs of pregnant and lactating people in how they make decisions about using cannabis during pregnancy and lactation. The second describes the perspectives, attitudes and beliefs of prenatal or postpartum health care providers on cannabis use during pregnancy or lactation and their experiences providing counselling to patients around this topic.
Panday, J., Taneja, S., Popoola, A., Pack, R., Greyson, D., McDonald, S. D., Black, M., Darling, E., & Vanstone, M. (2022). Family Practice, 39(3), 504-514.
This article received the 2022 Family Practice/North American Primary Care Research Group Best Paper award.
Vanstone, M., Panday, J., Popoola, A., Taneja, S., Greyson, D., McDonald, S. D., Pack, R., Black, M., & Darling, E. (2022). Journal of Midwifery & Women’s Health, 67(3), 354-372.
For this phase we explored how people make decisions about cannabis use during pregnancy and breastfeeding. This included their information needs, preferred sources of information, perceived risks, strategies to lower risks and desired clinical counselling approaches.
We recruited participants with the following characteristics:
We interviewed participants to better understand their experience navigating this decision-making process.
Taneja, S., Panday, J., Popoola, A., Greyson, D., McDonald, S. D., Patel, T., & Vanstone, M. (2023). Birth, 50(3), 504-512.
Vanstone, M., Taneja, S., Popoola, A., Panday, J., Greyson, D., Lennox, R., & McDonald, S. D. (2021). CMAJ: Canadian Medical Association Journal, 193(50), E1906.
Popoola, A., Panday, J., Taneja, S., Greyson, D., McDonald, S. D., Patel, T., Darling, E., & Vanstone, M. (2023). Women’s Health.
Cernat A, Carruthers A, Taneja S, Popoola A, Greyson D, Panday J, Darling E, Mcdonald SD, Black M, Murray, Davis B, Vanstone M. Birth. 2024;51(4):867–77.
For this phase, we explored what prenatal and postpartum care providers think helps or hinders them in supporting informed decisions when counselling people about cannabis use during pregnancy and breastfeeding. We recruited participants with the following characteristics:
We interviewed participants such as family physicians, midwives, and obstetricians.