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Experts say the science still isn’t clear about the health effects of cannabis in breast milk. Vera Livchak/Getty Images
  • Researchers say a new study did not find any harmful effects to infants from THC in breast milk from mothers who use cannabis.
  • Experts, however, say there hasn’t been enough research done on the topic to say if using cannabis during breastfeeding is safe.
  • Most medical professionals still recommend breastfeeding mothers abstain from using cannabis until more studies are done.

Is it safe for some THC to be passed along to a baby in breast milk?

OB/GYNs say that question is coming up more often with the legalization of cannabis sales and the push for using the drug as a natural alternative over other medications and easier access to those products.

It’s time, they say, to dig deeper on the topic.

A study presented on Oct. 8 at the virtual American Academy of Pediatrics National Conference & Exhibition could be a start.

The research, which hasn’t been published or peer-reviewed yet, analyzed the medical records of 763 early preterm infants from 2014 to 2020.

Researchers found that 17 percent of their mothers tested positive at the time of delivery for tetrahydrocannabinol (THC), one of the active ingredients in marijuana, an indication that some women are using cannabis during and after pregnancy.

Overall, the study found, early preterm babies born to mothers who tested positive for marijuana were similarly healthy by the time of their discharge when fed their mother’s breast milk compared to those who did not receive their mother’s breast milk.

Dr. Natalie L. Davis, MMSc, a lead author of the study and an associate professor of pediatrics at the University of Maryland School of Medicine and a neonatologist at the University of Maryland Children’s Hospital, told Healthline that more research is needed before saying THC passed to babies in breast milk is safe.

“It is really challenging to draw firm conclusions from my study because a lot more research needs to be performed to fully understand the risks,” she said. “This study is just the beginning.”

Davis said she was motivated to do the study after hearing about a hospital that did not support a mother in breastfeeding her premature baby because she tested positive for THC.

“This new mother really wanted to breastfeed her baby because she knew breast milk was extremely beneficial, and she wanted that bonding experience,” Davis said.

But when she tested positive, Davis said, “they wouldn’t help order her a breast pump, provide any lactation consultation help, or assist in her feeding her baby breast milk because of her THC status. She was really devastated, and her family wanted to know more about the health risks this situation would pose to babies.”

That, Davis said, “inspired me to explore the issue more, to help better inform new mothers and their doctors about how the benefits of breast milk compared to any possible health risks from THC.”

Dr. Kathryn Gray, an attending physician at Maternal-Fetal Medicine at Brigham and Women’s Hospital and an assistant professor at Harvard Medical School in Massachusetts, told Healthline she has seen a possible increase in the use of cannabis by pregnant and nursing people.

With that in mind, she hopes to see more data on what that could mean.

“I think there is a lot more use, and perhaps it is even underestimated by us,” Gray said. “It highlights how important (more study) is for us because clearly, [cannabis use] is more and more common.”

Gray said the current lack of detailed information leaves medical professionals like her only one option: to counsel pregnant and nursing mothers not to use cannabis products at that time.

She pointed to two studies that have given some glimpses of information. One published in 2018 found that only about 2 percent of the maternal dose of THC passes along via breast milk to the baby.

The research did not, however, look at whether that amount was a danger.

Other studies, Gray said, have found that THC lingers in the mother’s body and is passed along via breast milk for at least 8 days and possibly longer.

Davis said that means the “pump and dump” method adopted by nursing mothers who want to, say, enjoy a glass of wine is not an option.

These research findings, Davis said, have not been enough to form a concise recommendation.

“It’s a shame we don’t have any evidence-based science” to help form a solid platform to counsel patients from, she said.

Davis said that’s exactly why she took on this first study.

“Because we know that THC does accumulate in the breast milk and can be passed to the baby via breast milk, we do still suggest mothers avoid THC use,” she said.

“Especially with premature babies, whose brains and other important organs are still developing, we just don’t know what the long-term effects will be on brain development and growth,” Davis said.

She hopes more studies will dig deeper, follow children longer, and look at school performance and behavior.

“It would be amazing to be able to follow these babies longer term, to know more about their health after they leave the hospital. Are they similar or behind in their developmental milestones? How often are they taken to the urgent care or the emergency department? Do they have other illnesses or medical problems when compared to kids who were not THC exposed?” she said.

“Key factors like that would help us evaluate if early THC exposure impacts their long-term health into childhood and eventually into adulthood,” she added.

Gray noted that cannabis, in general, has been a moving target of information in recent years.

“We’ve osculated over time in how we look at it,” she said. “It’s been tricky.”

For now, though, Davis and Gray agree that the current practice of suggesting nursing mothers cease using cannabis for the nursing time needs to stand.

“We still don’t have data on longer-term impacts, which would be really important to know when making decisions on this issue,” Davis said.

“That is why we still recommend women who plan to become pregnant and breastfeed, or those who are pregnant or who are breastfeeding, avoid all marijuana use, including exposure to THC products,” she said.