Medically Reviewed by
Jason Crawford

Article Last Updated on January 10, 2023

Cannabis has been around for ages, but as its legality increases state-wide, as we have witnessed in the last few years, so does its use. With the public perception of weed changing, many people now use weed either as medical marijuana or recreationally, and while we’re at it, we’re still learning about its benefits and drawbacks.

With that being said, many mothers-to-be and nursing mothers use marijuana for various reasons. But seeing how little we know about pregnancy and marijuana, many questions are being asked, such as how long cannabinoids stay in the mother’s milk and whether the use of marijuana during lactation is safe for the baby. 

The benefits of breast milk for the newborn are undisputed, which is why it’s so important to know how long marijuana stays in breast milk and whether there are any health risks, which is what we discuss in today’s article.

How Do Cannabinoids End Up In Breastmilk?

When you consume cannabis through any method, your body starts to metabolize it in order to eliminate it. However, cannabinoids are harder to eliminate at one go because they are lipophilic, meaning they attach themselves to body fat. 

The body metabolizes the cannabinoids slowly. They get turned into byproducts called metabolites and they bind themselves to the fat cells in the body and stay there for a while. Depending on the quantity and frequency of use, they may take a few days to a few weeks to be completely eliminated.

It’s thought that one way cannabinoids end up in breast milk is because the human body uses the fat cells to fuel milk production. Therefore, cannabis that entered the bloodstream days or even weeks before, may still end up in human milk. Another way that cannabinoids can make their way into breast milk is through the blood vessels in the breast that have access to the milk ducts.

How Long Does THC Stay In Mother’s Milk?

THC (tetrahydrocannabinol) is the main psychoactive component in marijuana. Unlike its sibling, CBD (cannabidiol), THC is a compound of concern in this case because of its psychotropic properties. We already said that cannabinoids linger in the body for a while because they’re stored in the body fat, but just how long does THC remain in mother’s milk?

Considering the legality of weed changing and its use increasing, this is a very important question that is only beginning to be explored. From the studies conducted so far, it seems like THC stays in breast milk for longer than just 24 hours. 

THC Is Detectable In Breast Milk

A 2018 study published in the journal Obstetrics and Gynecology examined whether THC is detectable in breast milk. In the study, breast milk samples were collected from nursing mothers who were regular cannabis users. For the purposes of the study, the mothers smoked 0.1g of marijuana with 23.18% THC. The results of the study showed that low levels of THC were detected in the milk and that the infants “ingested an estimated mean of 2.5% of the maternal dose”.

THC Can Stay In Breastmilk for a Few Days to a Few Weeks

A similar study from the same year, conducted by the University of California, San Diego, and published in the journal Pediatrics, focused on how long THC stays in human milk after smoking marijuana. It was a longitudinal study that lasted from 2014 to 2017 during which 50 nursing mothers (most of which smoked weed daily and the rest ingested weed) donated samples from their breast milk to be tested for the presence of THC. It was discovered that traces of THC could be found up to six days after marijuana use.

However, a new study seems to show that THC can linger in breastmilk for longer than just six days as it was previously discovered. A 2021 study published in JAMA Pediatrics was designed taking into account the previous studies done on breast milk and cannabis. The mothers were all regular cannabis users during their pregnancies, who agreed to abstain from cannabis use for six weeks postpartum while the study lasted. 

The final results revealed that all of the women had detectable amounts of THC in their breast milk for up to six weeks. The concentration of THC varied from woman to woman because of their different cannabis usage habits, but it was detectable nonetheless.

Does THC Have Negative Effects on Newborn’s Development?

Even though these studies on cannabis and its presence in breast milk have been conducted, the effects of cannabis on a newborn’s development remain unclear. 

While the estimated THC percentage found in breast milk is low, meaning that the infant will also ingest small amounts of THC, it should still be noted that THC has powerful psychotropic properties and infants are highly vulnerable, so even a small amount of THC may have an irreversible negative impact. THC affects the prefrontal cortex, the part of the brain responsible for key cognitive functions, so exposing the infant to these changes so early on seems risky.

In fact, a 2018 article on marijuana use during pregnancy and nursing, published in the journal Obstetrics and Gynecology, discusses previous literature and findings from both human and animal studies. The researchers suggest that cannabis use during lactation and pregnancy may lead to different kinds of negative outcomes for the infants, such as neurobehavioral problems, growth restriction, congenital anomalies, and spontaneous preterm birth, to name a few.

Should Breastfeeding Mothers Stop Using Cannabis During Lactation Period?

Do the benefits of mother’s milk outweigh the possible risks of THC? We don’t know yet. However, the American Academy of Pediatrics has published a clinical report in order to provide some guidance given the lack of research. They discourage all pregnant women and mothers who breastfeed from using marijuana during this period due to concerns about fetal and brain development, and potential neurodevelopmental and behavioral problems. 

However, they still note that mothers should still be informed about the lack of research, and also be counseled about the potential adverse effects of marijuana on their babies if they decide to breastfeed.

Finally, experts also note that smoking weed may impair a mother’s ability to take care of her child and meet their needs.

Can Pregnant Women Continue Smoking Marijuana?

Given the findings at present, it is not advisable for pregnant women to smoke weed due to the potential negative effects of cannabis on fetal development. Simply said, we don’t have enough information to take that risk. Additionally, in some states, like Colorado, it’s illegal to use marijuana while you’re pregnant or breastfeeding. If your healthcare provider discovers that you’re a cannabis user, even if you live in a state where marijuana is legal in any form, they’re obliged to report it to Child Protective Services.


Marijuana use has become increasingly prevalent with the changing state laws, but it also urges the need to address and research important questions, such as the presence of cannabinoids in weed. Several studies have already shown that THC can be detected in breast milk for up to six weeks after consumption, but it’s still unknown what effect this can have on the development of newborns. Due to the lack of research, mothers-to-be and breastfeeding mothers are both advised to abstain from cannabis use during this crucial period of their infants’ lives.

A passionate advocate for the benefits of cannabis. Fraser Horton, who has a background in botany and a strong love of nature, has spent years researching how cannabis affects the body and mind. He established Leaf Nation in 2020, where he has devoted himself to educating people about the legalisation of marijuana and its safe and responsible use. Fraser is committed to highlighting cannabis’ potential for improving wellness and working to dispel the stigma associated with its use.


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