Low levels of delta-9-tetrahydrocannabinol (THC), the main psychoactive component of cannabis, transfers to breast milk in mothers who smoke it, a small pilot study suggests.
Although the long-term neurobehavioral effect of exposure to THC on the developing brain is unclear, mothers should be “cautious using cannabis during pregnancy and breastfeeding,” the investigators warn.
“We thought it was important to do this study, and from this study, we can tell women that it transfers in low amounts, and any amount is concerning,” Teresa Baker, MD, from Texas Tech University Health Sciences Center, in Amarillo, told Medscape Medical News.
The study was published online April 9 in Obstetrics and Gynecology.
The secretion of small to moderate amounts of THC into breast milk has been reported in some older studies. However, such studies may not adequately represent the levels of THC found in breast milk today, given the amounts of THC present in newer commercialized cannabis products.
To investigate, Baker and colleagues conducted a pilot pharmacokinetic study involving eight women who smoked cannabis and were exclusively breastfeeding their 2- to 5-month-old infants. Seven of the women were occasional cannabis users, and one was a long-term user.
The women were instructed to refrain from using cannabis for 24 hours and to then collect a baseline breast milk sample, after which they were to smoke a preweighed, standardized strain of cannabis from one preselected dispensary in Denver, Colorado (0.1 g, containing 23.18% THC, inhaled in three to four hits during a period of 10 to 20 min) and to then collect additional breast milk samples 20 min, 1 hr, 2 hr, and 4 hr after inhalation.
The investigators detected low levels of THC in the breast milk samples at all time points beyond baseline.
The average concentration of delta-9-THC in breast milk was 53.5 ng/mL. The mean maximum concentration in breast milk was 94 ng/mL, which occurred 1 hr after smoking.
The daily absolute infant dose was estimated as average consumption multiplied by an average breast milk intake of 150 mL/kg/day. The estimated infant dose, relative to the maternal dose, was 2.5% (range, 0.4% to 8.7%), and the average absolute infant dose was estimated to be 8 μg/kg/day.
THC “definitely transfers” to breast milk, “and the kinetics match what we anticipated,” said Baker.
“Does it stack or go back to baseline every time? That’s what people really need to know,” said Baker. “And, of course, the most important question is how much the baby is absorbing, but that’s a pretty tough study to do.”
Studies are also needed to assess the transfer of THC in oral cannabis preparations to breast milk, “because the pharmacokinetics when you take the drug orally is much different,” Baker said.
Many Questions Remain
In a podcast discussing the reasons the study was selected for publication, Nancy Chescheir, MD, editor-in-chief of Obstetrics and Gynecology, said this study is very small and may be an “outlier” for the journal.
On the flip side, this kind of data is “really hard to get for lots of different reasons,” and the researchers had to go to “great lengths to even get these eight women to participate,” said Chescheir, a clinical professor of obstetrics and gynecology and a maternal fetal medicine specialist at the University of North Carolina at Chapel Hill School of Medicine.
Many questions remain, including what effect repeated and continuous marijuana smoking has on breast milk concentrations, and much more study on this topic is clearly needed, but “having some data to start with is better than no data and making assumptions,” said Chescheir.
The topic is an important one, given the increase in legalization of marijuana for medical and recreational purposes, she added.
“A growing number of states allow medicinal and recreational use of marijuana within their state. So we really felt that this was a paper that would move that line of inquiry further to be able to understand in the future what kind of exposure babies are getting and how that may affect, or not, their neurodevelopment,” said Chescheir.
The study received no commercial funding. The authors have disclosed no relevant financial relationships.
Obstet Gynecol. Published online April 9, 2018. Abstract