Learn About Substance Use and Pregnancy

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Author: Centre for Addictions Research of BC


For references to the studies discussed in this info sheet, see the reference list.

What are substances?

Substances are psychoactive (mind-altering) drugs that affect how we think and feel. They tap into the wiring system of the human brain and influence the way nerve cells send, receive or process information. Some drugs decrease our heart rate, breathing and mental processing (e.g., alcohol, benzodiazepines or heroin). Others increase our heart rate, breathing and mental processing (e.g., caffeine, tobacco or cocaine). Using some of these substances during pregnancy can impact the health and development of the fetus.


Why do we use substances?

People use substances for all sorts of reasons. For some, substances play a role in ceremonies or serve to mark special occasions (e.g., a toast at a wedding). For others, substances are used to cope with life pressures, pain or anxiety. And for still others, substances are used to relax, connect with others or have fun.

While substances can be beneficial, they can also be harmful. In particular, alcohol and other drug use can have serious consequences for a pregnant woman and her unborn fetus. Sexually active girls and women may choose to drink alcohol at low-risk levels or not use alcohol and other drugs in certain situations, such as when pregnant or planning to become pregnant. While using substances may help with temporary stress, using during pregnancy may increase the risk of harm to the fetus.


What happens when we use substances during pregnancy?

When we use a substance during pregnancy, the fetus is exposed to its effects. But it is difficult to predict for certain the impact of substance use in every case, because every mother and every fetus is different. Certain things about the substance—the type, the amount, frequency of use, and method of use—influence the degree of risk. Other factors may also affect a growing fetus. These include a pregnant woman’s physical and mental health, access to nutrition and prenatal care, exposure to violence, and family relationships.

Substance use during pregnancy may also affect the later development of the infant and child. For instance, prenatal exposure to some substances is linked to increased risk of difficulties with learning and behaviour. But researchers point out it is important to consider these links in the context of other factors that affect child development, such as genetics, parenting styles and social environment.

With this backdrop in mind, the following is a brief look at what the research can tell us about the effects of using substances during pregnancy.


Drinking alcohol during pregnancy can be linked to miscarriage, premature birth, low birth weight and a range of life-long physical, mental and behavioural effects under the term Fetal Alcohol Spectrum Disorder (FASD). FASD includes difficulties with language, poor impulse control, and problems in attention or judgment, which can in turn affect success in school and all other areas of life.

Regularly consuming alcohol above the levels recommended by Canada’s Low-Risk Alcohol Drinking Guidelines, meaning having more than two drinks per day or 10 drinks per week, increases the risk of harm to the fetus. Some studies suggest very light consumption during pregnancy is of low risk (i.e., no more than 1.5 drinks on any occasion and less than five drinks per week). But given the potential for misunderstanding drink sizes and the possibility of harm to the unborn child from even light drinking, it is safest to avoid alcohol when pregnant and while breastfeeding, as alcohol passes into breast milk and can affect the infant.


Consuming more than moderate levels of caffeine during pregnancy may increase risk of harm to a developing fetus. While the findings from studies have been inconclusive, some researchers suggest that a pregnant woman who consumes more than 300 mg of caffeine per day (i.e., about two cups of coffee) may give birth to a baby smaller in size than normal and with a low birth weight.


Cannabis use during pregnancy may increase the risk of a woman giving birth to a baby smaller in size than normal and with a low birth weight. Research findings are conflicting on the effects of prenatal exposure to cannabis on learning and behaviour in children. Some evidence suggests regular use during pregnancy may be linked to subtle effects, including difficulties in impulse control, attention, verbal skills and memory. More research is needed to determine whether or not these effects have long-lasting consequences.


A woman who uses cocaine during pregnancy may give birth prematurely or have a baby shorter in length than normal and with a low birth weight. Studies suggest prenatal cocaine exposure may increase the risk of cognitive and behavioural effects in children and adolescents, including difficulties with attention, self-regulation, learning and memory. Some evidence suggests that the impact of these effects on school performance and achievement may be modest.

Heroin and Methadone

Using heroin during pregnancy is linked with increased risk of premature birth, reduced fetal growth and low birth weight. These negative effects are also linked to mothers who experience poor health and repeated withdrawal from heroin. When a mother receives methadone maintenance treatment, withdrawal is reduced and the mother’s health and prenatal care is improved. This in turn reduces problems for the baby.

Babies who are prenatally exposed to heroin or methadone may experience withdrawal symptoms at birth which need medical monitoring. Research findings are conflicting, but some studies suggest children exposed to heroin or methadone during pregnancy may have increased risk of learning difficulties. It is safest to avoid using heroin when breastfeeding as the drug passes into breast milk and can affect the infant. Methadone use when breastfeeding is considered safe for the baby.


Inhalants are products that give off chemical vapours. Many inhalants are volatile solvents—gasoline, paint thinner, glue—used to perform everyday household tasks. They are not intended for inhalation. Inhalant use during pregnancy is linked with increased risk of premature birth, low birth weight and physical effects. Prenatal exposure to highly concentrated inhalants may have impacts on the child’s development, including delayed growth and problems with speech and motor skills. Available research cannot answer whether these effects last into adolescence and adulthood.


Certain over-the-counter and prescription medications may increase risk of harm to a fetus. For example, some analgesic medications include caffeine. Using more than the recommended dosage, or combining the medication with other caffeinated products, may lead to exceeding the suggested daily limits of caffeine for pregnant women.

Some prescription medications are safe for use during pregnancy, but some may increase risk. For example, a woman who uses benzodiazepines (tranquilizers) such as Valium and Ativan during pregnancy may give birth prematurely or have a baby with low birth weight. Taking the time to read the labels on medications or consulting with a healthcare professional can help reduce risks.


Using methamphetamine during pregnancy increases the risk of having a baby smaller in size than normal and with a low birth weight. Very little is known about the effects of prenatal exposure to methamphetamine on children and adolescents. Some research suggests there may be impacts on the child’s development, including difficulties with motor skills, attention and memory. But research cannot answer whether these effects have long-term significance.

MDMA (Ecstasy or Molly)

Few studies have been conducted on the effects of MDMA during pregnancy. However, the available research suggests regular prenatal exposure to MDMA may increase risk of delays in motor skills in infants.


Smoking during pregnancy is connected to miscarriage, decreased fetal growth, premature birth and low birth weight. Exposure to second-hand smoke when pregnant also may harm the fetus. It is linked to increased risk of miscarriage and giving birth to a baby with low birth weight. Some studies suggest prenatal exposure to tobacco smoke may increase risk of learning and behavioural problems in children, including difficulties with attention and aggression.


When is substance use during pregnancy a problem?

Using a psychoactive substance is a problem when it negatively affects our life or the lives of others. Many of us may think this refers only to people who regularly use large amounts. But we know that other patterns of alcohol or other drug use when pregnant or planning to become pregnant can present risk of harm to the fetus. Recognizing the potential for adverse consequences of use allows us to make choices that might reduce the risk.

Women who are pregnant, for example, may have trouble sleeping. While it may be tempting to induce sleep by taking tranquilizers or drinking alcohol, using these drugs during pregnancy may harm the fetus. But the situation is complicated by the fact that social and economic factors also influence the likelihood of adverse consequences. Women living in socially disadvantaged circumstances may not have access to adequate nutrition. Undernourished women who drink during pregnancy may be at increased risk of having a baby affected by FASD. So the choices that reduce risk extend beyond the individual lifestyle choices of an expectant mother to include the actions we all take (or don’t take) that shape our social and cultural communities.

The reasons we use substances influence our pattern of use and the risk of harmful consequences. For instance, if we use alcohol or cannabis to address anxiety or chronic stress, we may develop a pattern of repeated or daily use. But such a pattern during pregnancy exposes the fetus to greater risk.


How to make healthier choices about substances

Whenever we choose to use substances, it is helpful to know what steps we can take to ensure that our use is the least harmful possible.

  • The safest option when pregnant or when planning to become pregnant is to not drink alcohol or use other drugs.

  • If you’ve just found out you’re pregnant and have been using substances up until now, it is best to avoid use from now on.

  • It is important to check with a healthcare professional before taking medications.

  • If you choose to use substances, remember the guideline: not too much, not too often and only in safe contexts.

  • If you choose to drink alcohol while breastfeeding, store breast milk if planning to drink at levels that would result in alcohol still being present at the next feed. (To estimate blood alcohol content, visit this tool at: www.healthyfamiliesbc.ca/alcohol-bac.)

  • It is not all about substance use. Other ways to help reduce risk to the fetus include attending prenatal appointments, eating a healthy diet, exercising regularly and getting enough sleep.

  • Remember to follow Canada’s Low-Risk Alcohol Drinking Guidelines.


What to do if you or someone you know wants to explore change

To better understand how substances play a role in your life, visit the You and Substance Use Workbook. This website also features detailed information on substance use and mental health.

You can also find information about a wide variety of substance use issues on the Centre for Addictions Research of BC website: www.carbc.ca.

For pregnancy and breastfeeding information, call the Motherisk Alcohol and Substance Use Helpline at 1-877-327-4636, Monday to Friday, 9 a.m. to 5 p.m., or visit www.motherisk.org.


For information on treatment options and resources throughout BC, call the Alcohol and Drug Information and Referral Service at 1-800-663-1441. In Greater Vancouver, call 604-660-9382.


About the author

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The Centre for Addictions Research of BC is a member of the BC Partners for Mental Health and Addictions Information. CARBC is an official research centre of the University of Victoria. The Centre collaborates with service providers and other stakeholders to support effective public education, system planning, and service delivery. For more, visit www.carbc.ca.