Cannabis and Breastfeeding: What’s the Harm?

“We see that people perceive edibles as less harmful than smoking,” he says. “That means someone may be more inclined to take an edible while breastfeeding.” 

The medical guidance during pregnancy is clear: Don’t use cannabis. It gets more complicated in the postpartum period, however. The American Academy of Breastfeeding, for example, advises weighing the documented benefits of human milk and breastfeeding against the still-uncertain long-term developmental effects for infants who are exposed only during lactation.  

That’s a key period of time, though. People who abstained from cannabis during pregnancy may resume use as they encounter new parent stressors, points out Skelton. Plus, postpartum mental health concerns such as depression and anxiety might prompt new mothers to consume cannabis—even though the science doesn’t support that use, she adds.  

Unlike alcohol, which typically leaves breastmilk in several hours, THC can be found for at least six days after consumption. That’s because the compound is attracted to the body’s fatty tissues. The more someone consumes, the more THC accumulates in breastmilk’s high fat content.  

“Everyone understands that if you’re drunk, you shouldn’t breastfeed your baby, but people don’t understand the science here,” Skelton says.  

In the short term, using cannabis while breastfeeding can lead to drowsier babies, some observational evidence has shown. Lethargic babies may eat less often, which could result in poor weight gain and a need to supplement with formula. Animal studies have shown that THC can inhibit the production of prolactin, a hormone responsible for lactation.  

The long-term consequences on brain development pose a bigger question. Some studies looking at cannabis use during pregnancy have shown that maternal marijuana consumption is associated with a higher risk for executive function deficits later in life, such as impulse control and attention skills.  

“It’s hard to differentiate out the neurodevelopmental consequences, and the evidence is still growing,” Skelton says. “But it’s something that’s being discussed more and more.” 

Complicating the discussion are the disparities in breastfeeding rates, says Stacey Iobst, PhD, RNC-OB, who studies maternal health at Towson University in Maryland. Some of the same groups that have lower breastfeeding rates are the ones using more cannabis, such as low-income women.   

“Those disparities are potentially going to widen if people completely avoid breastfeeding,” she says. “We can’t just say don’t use cannabis and send them out the door. That’s not a winning strategy from a public health perspective.” 

She’d like to have better clarity on the harmful effects, information that can help patients make informed decisions. In the future, researchers like Skelton are also interested in exploring provider communications as well as the role of household exposure, such as from a dad who smokes outside but then holds an infant. 

On Maryland’s Eastern Shore, perinatal nurse Jaimi Hall, MSN, RNC-OB, says those questions are pressing, especially with so many patients—and household members—using the substance. As she walks through the hospital, she often inhales the skunky odor still clinging to people’s clothing. New moms tell her they use cannabis to ease chronic pain, nausea, depression, and anxiety.  

When they discuss breastfeeding, Hall shares that THC accumulates in breastmilk. For people with mental health disorders, Hall suggests alternatives such as antidepressants that are safe during breastfeeding. But convincing patients to curtail cannabis is a hard sell when there’s a lack of strong evidence, she says. Without that, Hall faces the same quandary as Fenner, the lactation group leader across the country. 

“We know there are all those wonderful benefits of breastfeeding, but we don’t know what happens when you’re breastfeeding with marijuana,” she says. “I’m hoping that changes.”