Is Weed Safe When You're Breastfeeding?

There are two important factors: how long THC stays in the bloodstream, and whether it has a negative effect on babies.
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Asking for A Friend has the answers to health and wellness questions that you personally don’t need to know, but someone might.

Once you've been pregnant for nine months, the whole worshiping your body as a temple thing can start to wear a bit thin. You may become a bit resentful of having to pass over beer yet again, and what if you want something a little stronger still?

The increasing legalization of cannabis has led to a great “thirst for information” on this subject said Heather Thompson, Deputy Director at Elephant Circle, a birth rights organization based in Denver.


“Almost everybody asks me, ‘Is it safe? Give me the lowdown,’” she said. “I don’t ever use the terminology that cannabis is ‘safe,’ as I can’t define safe for somebody else, and really everything you do during pregnancy or breastfeeding is a risk benefit analysis. I mean, driving is not a safe activity.”

Thomas Hale, associate dean of research at Texas Tech University Health Sciences Center and author of Hale's Medications and Mother’s Milk said that we don’t really know if cannabis is safe at all—for breastfed babies or even for adults. “We are just at the beginning of our learning about what marijuana is all about and how it works and where it goes, and we just don’t have enough good science on it yet,” he said.

Hale said that there are currently two main questions that need answering: 1) Does cannabis get transferred into the breast milk?, and 2) Does cannabis exposure have a negative effect on babies? So far, he said, only a handful of studies have looked at the impact of cannabis use on breastfeeding.

To answer the first question, Hale and Thompson both worked on a pharmacokinetic study published in Obstetrics & Gynecology in May 2018 to find out whether tetrahydrocannabinol (THC) was detectable in the breast milk of women who had used a known amount of it.

The results showed that while THC is definitely detectable in breast milk, it was at a concentration of about 2.5 percent of what the mother had taken. “The baby has to absorb [the THC] orally from breast milk and it is very poorly absorbed, maybe 1-5 percent,” Hale said. “So if the mother… transfers 2.5 percent to her milk, only 1-5 percent [of that] is going to be absorbed by the baby. You can see how the dose is actually getting lower.”


Thompson said the research showed that THC is metabolized out of the breast milk at a rate similar to that of alcohol. “For the majority of subjects in that study, after 24 hours of abstaining from cannabis, they had undetectable amounts of THC in their breast milk, which came back down to nearly the baseline at four hours after consumption.

“So in the same way we talk about alcohol—you know, if you want to drink a beer while you are chestfeeding your baby, then you drink that beer and then wait two hours until you feed that baby again—I think we can have a similar conversation about cannabis” she said.

Chronic users, however, took much longer to achieve a THC level that was undetectable, and the paper warned that complete elimination could take up to four days.

As for the second question, according to Crume, if breast milk that has traces of THC is consumed by a baby, it could have an impact on babies’ development. She said that cannabinoids (of which THC is one) go into the bloodstream, and can therefore affect the brain. Additionally, cannabis is known to impact the prefrontal cortex, a part of the brain that isn’t fully developed until a person is 25.

There are a lot of benefits to breastfeeding—so many in fact, that experts don’t tell smokers to stop breastfeeding despite the risks of tobacco being clear and myriad. “What is unclear is if the potential risk of cannabinoids outweigh the benefits of breastfeeding,” Crume said.

While experts say there needs to be more research done on the effects of all drugs on breastfeeding mothers and their babies, there is one drug-related breastfeeding myth that Thompson wants to put to rest: that cannabis accumulates in breast milk because it is fatty.

“One of the questions I get a lot is that ‘breast milk is full of fat, and babies are full of fat, and THC ‘loves’ fat [meaning THC is lipophilic, or can be stored in body fat], so it is going to accumulate or concentrate in breast milk,’” she said. “And that is patently untrue, that is just a false statement.” In fact, she added, it is physiologically impossible. THC is also only stored in adipose tissues—not fat cells—and these tissues are separate from the milk ducts where milk is made.

Evidence shows that the best way to minimize exposure to cannabis via breastfeeding is for the person using weed to do so infrequently, and to wait for at least 24 hours (and maybe as long as four days) for the body to metabolize the THC before breastfeeding. But it is still unclear whether the risks of using cannabis while breastfeeding actually outweigh the undeniable benefits of breastmilk for infants.

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