How Much THC Ends Up In Breast Milk?

The breast milk study, published in Obstetrics & Gynecology, found that about 2.5 percent of the mother’s cannabis dose ended up in her breast milk. For example, if a mom consumes 10mg of THC from smoking a joint, roughly a quarter of a milligram will end up in the milk. That may not seem like child’s play to the typical stoner, but it could affect an infant’s neurological development says Dr. Teresa Baker, an OBGYN and the study’s primary author.

“We have no idea what that means for the offspring,” told Baker, regarding the 2.5 percent value. “If there’s chronic exposure [to the infant], how high can that [THC level] be” to ensure the child’s safety?

To obtain milk samples, Baker’s team at Texas Tech University collected breast milk samples from eight nursing mothers that “regularly” smoked weed. A baseline milk sample was taken 24 hours before smoking. Afterward, the mothers smoked 0.1g (about a small bowl’s worth) of a 23-percent THC strain. Four more milk samples were taken at timed intervals after inhalation: at 20 minutes, 1 hour, 2 hours and 4 hours. THC levels were detected with a high-performance liquid chromatography system (HPLC), the same instrument cannabis testing labs use to measure THC in samples of dry bud.

Although doctors have known that cannabinoids can transfer from mother to infant for decades, investigations into how much THC ends up in the infant and how quickly it clears out of the mother’s body have been lacking. The Obstetrics & Gynecology study also comes at a time when 70 percent of Colorado’s pot shops are recommending cannabis to pregnant mothers. (Note, the Colorado study didn’t survey dispensary recommendations to nursing mothers.)

Dr. Allen Frankel, an internal medicine specialist, agreed that more studies need to be done. “There is just not adequate data on this to know,” he wrote in an email.

Previous studies assessing how cannabis affects child development are inconclusive. For example, a 1991 Jamaican study followed 59 kids from birth to five years of age and discovered no developmental differences between kids raised by cannabis-consuming mothers and mothers who abstained. (Interestingly, at the age of 30 days, the “user” group of infants showed “more favourable scores” on “autonomic stability and reflexes.”)

Yet other studies, such as this Austrian one from 2014, found evidence that THC could interrupt the formation of neural connections in the fetal brain. Phytocannabinoids like THC mimic human endocannabinoids that are critical for hormone signaling during the early stages of human development. Conversely, human breast milk naturally contains endocannabinoids, an evolutionary adaptation that stimulates hunger and facilitates social bonding between mother and infant. But whether the addition of phytocannabinoids could alter a fetus or an infant’s neurological development requires more investigation.

“My advice to a patient is to do their best to avoid [cannabis while nursing], but if needed for the mother’s medical reasons, I personally doubt it is a really big deal,” added Frankel, who is also the founder of GreenBridge Medical, a medical cannabis consulting firm based in Santa Monica, California.

Among the top reasons pregnant and nursing mothers consume cannabis is to prevent nausea and vomiting caused by maternal hyperemesis syndrome, a severe form of morning sickness. Many “obstetricians are actually OK with [mothers] using cannabis,” Frankel wrote, “as it is most likely much safer than pharma meds.”

The reality is, most moms who spark up will likely keep toking until conclusive science determines that minute quantities of THC are, without a doubt, dangerous for infants. Given this, Baker recommends taking a safe approach. According to her study and others, THC levels in the mother’s bodily fluids “reach a peak at about one hour” after consumption, she said.

“How mothers use that information to avoid infant exposure is up to them, but I’d say don’t do it. Ever. I’d say abstain from cannabis products for 24 hours [before pumping or feeding],” Baker explained. “The longer they can wait, the better.”