News, Culture & Society

New mothers who smoke cannabis could pass on chemicals while feeding and damage their baby’s brain

New mothers who smoke cannabis and breastfeed could be getting their babies high and affecting their brain development.

A study has revealed the chemical in marijuana which gives smokers a high can stay in women’s breast milk for up to six days.

THC, which is the psychoactive part of cannabis, can stick to fat molecules in a woman’s milk meaning it passes into the baby during breastfeeding.

And the experts who did the research say it is possible the drug could have an impact on an infant’s brain development.

They recommend women quit using marijuana while breastfeeding to make sure their babies are not harmed. 

Smoking cannabis could cause the psychoactive chemical THC to pass into breast milk and stay there for up to six days, suggesting babies might consume it, researchers say

The study by scientists at the University of California in San Diego tested breast milk samples of 50 women who smoked marijuana.

Of 54 samples taken, 34 of them – 63 per cent – still contained THC up to six days after the milk was produced.

THC, scientifically named tetrahydrocannibinol, is the psychoactive ingredient of cannabis and is what makes the drug illegal in the UK.

And while it can make people feel relaxed or happy, the drug has also been linked to worse memory and learning abilities, and an increased risk of mental health problems like depression.

Cannabis in breast milk ‘could influence normal brain development’ 

The authors of the said it is ‘reasonable to speculate’ that exposing infants to THC or another chemical called cannabidiol ‘could influence normal brain development’.

‘We still support women breastfeeding even if using marijuana but would encourage them to cut down and quit,’ Dr Seth Ammerman in a recent report by the American Academy of Pediatrics.


Pregnant women who smoke cannabis risk causing damage to their unborn baby’s brain, experts warned in 2016.

The drug is linked to abnormal brain structure in children, a study by the Erasmus University Medical Center in Holland revealed.

Children exposed to marijuana in the womb were found to have a thicker prefrontal cortex region of the brain, when compared to children not exposed to the drug.

The prefrontal cortex is a region of the brain that is linked to decision-making, memory and personality, and changes to the tissue could affect how the brain works.

Scientists examined brain scans of 54 children exposed to cannabis in the womb, 96 children exposed to just tobacco, and 113 children with no exposure to either drug.  

They noted differences in the thickness of the prefrontal cortex – it was thicker in children exposed to cannabis, suggesting their memory and personality could be affected.

The researchers said their findings, published in the journal Biological Psychiatry, suggest cannabis exposure has different effects than tobacco. 

The researchers explained THC can pass to breast milk because marijuana’s active compounds like to bind to fat molecules, of which there are a lot in breast milk.

This stickiness suggests the compounds can end up in breast milk, raising concerns about the potential effects on nursing babies.

It’s not known if the amounts of THC detected in the study pose any risk but researchers are studying children whose mothers’ were involved to try to find out.

‘We don’t know if there are safe levels for infants’ 

Dr Christina Chambers, the lead researcher in the study, said: ‘We found the amount of THC that the infant could potentially ingest from breast milk was relatively low.

‘But we still don’t know enough about the drug to say whether or not there is a concern for the infant at any dose, or if there is a safe dosing level.

‘The ingredients in marijuana products that are available today are thought to be much more potent than products available 20 or 30 years ago.’

Past research suggested developmental delays 

Two small studies from the 1980s had conflicting results on whether pot use affects breastfed infants.

One found no evidence of growth delays, as the other found slight developmental delays in breastfed infants, but their mothers had used pot during pregnancy too.

And while cannabis use is likely to be lower in the UK and Australia where it is outlawed, the drug is legal in nine US states and available on prescription in 31 states.

According to US government data, about one in 20 women report using marijuana during pregnancy.

Estimates for use among breastfeeding mothers vary, but a study in Colorado, where recreational marijuana is legal, put the number at almost 20 per cent among women in a government supplemental food program.

‘If women feel they have to choose they may stop breastfeeding’ 

Experts said it is important to not risk women choosing marijuana instead of breast feeding.

Dr Chambers added: ‘We don’t have strong, published data to support advising against use of marijuana while breastfeeding.

‘If women feel they have to choose, we run the risk of them deciding to stop breastfeeding – something we know is hugely beneficial for both mum and baby.’ 

The University of California’s findings were published in the journal Pediatrics.