(Date: January 2009. Version: 1)

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 Public Health England 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 are toxic and will 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 risk of having a low birth weight baby and could affect a child’s long term learning and behaviour. Cannabis is often smoked mixed with tobacco, and tobacco smoking during pregnancy has been strongly linked to certain pregnancy problems.

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 risks 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?

Although there is currently no scientific evidence that use of cannabis during pregnancy is linked to an increased risk of birth defects in the baby, only a small number of pregnant women using cannabis have been studied so far. Therefore, until more scientific information is collected we cannot say for sure that cannabis use in pregnancy does not cause birth defects.

Smoking tobacco in pregnancy is linked to an increased risk of cleft lip and/or palate (a split in the lip and/or the roof of the mouth) in the baby. It is not known whether smoking cannabis mixed with tobacco during pregnancy may further increase the risk of this birth defect in the baby.

Can using cannabis in pregnancy cause miscarriage?

No scientific studies have been carried out that have specifically investigated miscarriage risk in women using cannabis. Tobacco smoking in pregnancy has however been linked to an increased risk of miscarriage. It is not known whether smoking cannabis mixed with tobacco during pregnancy may increase this risk.

Can using cannabis in pregnancy cause stillbirth?

A single study showed a possible link between cannabis use in pregnancy and stillbirth, but because most of the cannabis users in the study had also smoked tobacco (which is itself known to increase the risk of stillbirth), it was not possible to say whether the increased risk was actually due to cannabis.

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

Studies that have investigated whether women who use cannabis during pregnancy are more likely to have a premature and/or low birth weight baby have produced mixed findings. When all of the scientific evidence is considered together, use of cannabis from mid-pregnancy onwards appears to carry the greatest risk of possibly causing a baby to be small at birth.

Tobacco smoking during pregnancy has been strongly linked to premature birth and low birth weight. It is not known whether smoking cannabis mixed with tobacco during pregnancy might increase the risk of these pregnancy outcomes further.

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.

Studies have shown that babies exposed to cannabis while in the womb are 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 and damaging effects on an unborn baby’s developing brain.

Several studies have now 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 look for the same problems and so the results can be difficult to compare. Additionally, some only investigate 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. 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 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 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

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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