(Date: July 2018. Version: 2)

This factsheet has been written for members of the public by the UK Teratology Information Service (UKTIS). UKTIS is a not-for-profit organisation funded by the UK Health Security Agency (UKHSA) on behalf of UK Health Departments. UKTIS has been providing scientific information to health care providers since 1983 on the effects that medicines, recreational drugs and chemicals may have on the developing baby during pregnancy.

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

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General information 

Up to 1 out of every 5 pregnancies ends in a miscarriage, and 1 in 40 babies are born with a birth defect. These are referred to as the background population risks.  They describe the chance of these events happening for any pregnancy before taking factors such as the mother’s health during pregnancy, her lifestyle, medicines she takes and the genetic make up of her and the baby’s father into account.

Medicines use in pregnancy

Most medicines used by the mother will cross the placenta and reach the baby. Sometimes this may have beneficial effects for the baby.  There are, however, some medicines that can harm a baby’s normal development.  How a medicine affects a baby may depend on the stage of pregnancy when the medicine is taken. If you are on regular medication you should discuss these effects with your doctor/health care team before becoming pregnant.

If a new medicine is suggested for you during pregnancy, please ensure the doctor or health care professional treating you is aware of your pregnancy.

When deciding whether or not to use a medicine in pregnancy you need to weigh up how the medicine might improve your and/or your unborn baby’s health against any possible problems that the drug may cause. Our bumps leaflets are written to provide you with a summary of what is known about use of a specific medicine in pregnancy so that you can decide together with your health care provider what is best for you and your baby.   

Every pregnancy is unique. The decision to start, stop, continue or change a prescribed medicine before or during pregnancy should be made in consultation with your health care provider. It is very helpful if you can record all your medication taken in pregnancy in your hand held maternity records.

Disclaimer: This information is not intended to replace the individual care and advice of your health care provider. New information is continually becoming available. Whilst every effort will be made to ensure that this information is accurate and up to date at the time of publication, we cannot cover every eventuality and the information providers cannot be held responsible for any adverse outcomes following decisions made on the basis of this information. We strongly advise that printouts should NOT be kept for any length of time, or for “future reference” as they can rapidly become out of date.

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