Date: July 2018, Version 2

What is cannabis?

Cannabis (dope, ganja, hash, marijuana, pot, weed) is a recreational drug that is most often smoked with tobacco. Cannabis contains over 100 chemicals, many of which can cross the placenta and reach the baby in the womb.

Is it safe to use cannabis in pregnancy?

There is evidence to suggest that using cannabis during pregnancy may increase the chance of having a preterm and/or low birth weight baby and could affect a child’s long-term learning and behaviour. Cannabis is often mixed with tobacco for smoking, and smoking tobacco during pregnancy has been strongly linked to certain pregnancy problems (please see the smoking bump for further details).

Pregnant women should therefore avoid the use of cannabis. Speak to your doctor or midwife if you need help to do this.

What if I have already used cannabis during pregnancy?

Because of the possible problems described above, once you know that you are pregnant, the best thing that you can do to support your baby’s well-being is to avoid any further use of cannabis.

Can using cannabis during pregnancy cause birth defects?

Until more scientific information is collected we cannot say for sure whether cannabis use in pregnancy might cause birth defects in the baby. Studies have identified possible links between cannabis use in pregnancy and a specific type of heart defect called ventricular septal defect, and also gastroschisis (where some of the baby’s internal organs protrude through a gap in the abdomen). However, only a small number of pregnant women using cannabis have given birth to infants with these birth defects, so more research is required to confirm these findings and to rule out links with other types of birth defect that have not yet been studied.

Tobacco smoking in pregnancy has been linked to a number of different types of birth defect and so smoking cannabis mixed with tobacco is likely to increase the chance of these birth defects in the baby.

Can using cannabis in pregnancy cause miscarriage?

The small number of studies carried out so far do not suggest a link between cannabis use in pregnancy and miscarriage. Tobacco smoking in pregnancy has however been linked to an increased chance of miscarriage. Women smoking cannabis mixed with tobacco may therefore more likely to have a miscarriage than non-smoking women.

Can using cannabis in pregnancy cause stillbirth?

Three studies have all shown a possible link between cannabis use in pregnancy and stillbirth. However, in at least one of these studies most of the cannabis users had also smoked tobacco (which is itself increases the risk of stillbirth). It was therefore not possible to say whether the increased chance of stillbirth was due to cannabis itself.

Can using cannabis in pregnancy cause premature delivery and low birth weight?

There is some evidence that women who use cannabis in pregnancy may have a higher chance of having a premature birth and a low birth weight baby. However, it is unclear whether these effects are caused directly by cannabis, or may be due to smoking cannabis mixed with tobacco, as tobacco smoking during pregnancy has been strongly linked to these pregnancy outcomes.

Can using cannabis in pregnancy cause other health problems in the child?

Withdrawal symptoms at birth (neonatal withdrawal)

Withdrawal symptoms are thought to occur as the newborn baby’s body has to adapt to no longer getting certain substances through the placenta. Neonatal withdrawal can be dangerous for the baby if left untreated.

There is some evidence that that babies exposed to cannabis while in the womb may be at increased risk of withdrawal symptoms at birth. If you have used cannabis in the weeks before delivery it is therefore important that your doctor and midwife are aware of this as your baby may require close monitoring and/or supportive treatment for a few days after birth. 

Learning or behavioural problems

A baby’s brain continues to develop right up until the end of pregnancy. It is therefore possible that exposure to certain substances at any stage of pregnancy could have a lasting effect on a child’s learning or behaviour.

The effects of cannabis on mood and emotion are due to the fact that it affects the brain. There are therefore concerns that using cannabis during pregnancy could have lasting effects on an unborn baby’s developing brain.

Several studies have shown that children whose mothers used cannabis during pregnancy are more likely to have problems with thinking, learning and behaviour, than children whose mothers did not use cannabis.

Studying whether children who have been exposed to a particular substance in the womb are more likely to have problems with their learning or behaviour can be difficult. The studies often do not investigate the same problems and so the results can be difficult to compare. Additionally, some only test children when they are young, and so we do not know whether they ‘grow out’ of any problems that are observed, or show more problems with their learning or behaviour as they get older. Finally, it is often not possible to separate the effects of cannabis exposure in the womb from exposures and other factors in the home environment after birth that can also affect learning and behaviour. More research into the potential effects of cannabis use during pregnancy on the long-term learning and development of the child is therefore required.

Will my baby need extra monitoring during pregnancy?

As part of their routine antenatal care most women will be offered a scan at around 20 weeks of pregnancy to look for birth defects and to check the baby’s growth.

Using cannabis during pregnancy would not normally require extra monitoring of your baby, although if you are a heavy user your baby’s growth and wellbeing may need to be monitored more closely.

Are there any risks to my baby if the father smokes?

No studies have specifically investigated whether cannabis used by the father can harm the baby through effects on the sperm, however most experts agree that this is very unlikely. More research on the effects of drug and medicine use in men around the time of conception is needed.

If the baby’s father (or any member of a pregnant woman’s household) smokes cannabis, second-hand smoke from the air can potentially be a source of exposure. Ideally, a pregnant woman should avoid breathing in cannabis and/or tobacco smoke from others, as well as not use cannabis herself.

Who can I talk to if I have questions?

If you have any questions regarding the information in this leaflet please discuss them with your health care provider. They can access more detailed medical and scientific information from

How can I help to improve drug safety information for pregnant women in the future?

Our online reporting system (MyBump Portal) allows women who are currently pregnant to create a secure record of their pregnancy, collected through a series of questionnaires. You will be asked to enter information about your health, whether or not you take any medicines, your pregnancy outcome and your child's development. You can update your details at any time during pregnancy or afterwards. This information will help us better understand how medicines affect the health of pregnant women and their babies. Please visit the MyBump Portal to register.

General information
Sadly, miscarriage and birth defects can occur in any pregnancy.

Miscarriage occurs in about 1 in every 5 pregnancies, and 1 in every 40 babies are born with a birth defect. This is called the ‘background risk’ and happens whether medication is taken or not.

Most medicines cross the placenta and reach the baby. For many medications this is not a problem. However, some medicines can affect a baby’s growth and development.

If you take regular medication and are planning to conceive, you should discuss whether your medicine is safe to continue with your doctor/health care team before becoming pregnant. If you have an unplanned pregnancy while taking a medicine, you should tell your doctor as soon as possible.

If a new medicine is suggested for you during pregnancy, please make sure that the person prescribing it knows that you are pregnant. If you have any concerns about a medicine, you can check with your doctor, midwife or pharmacist.

Our Bumps information leaflets provide information about the effects of medicines in pregnancy so that you can decide, together with your healthcare provider, what is best for you and your baby.