Study explores how cannabis use affects breast milk and lactation

By Dr. Liji Thomas, MDReviewed by Benedette Cuffari, M.Sc.Apr 3 2024

In a recent study published in Advances in Nutrition, researchers explored the impact of cannabis use during pregnancy and lactation. More specifically, they examined the effects of cannabinoids on lipid metabolism in the breast tissue and hormone receptors that regulate breast milk secretion and production.

Study: Maternal cannabis use during lactation and potential effects on human milk composition and production: a narrative review. Image Credit: Dmytro Tyshchenko / Shutterstock.com

Cannabis use

Cannabis or marijuana is used by over 200 million people worldwide. Recently, cannabis use has been legalized for both medicinal and recreational purposes in many regions of the United States, as well as other countries. Current estimates indicate that up to 20% of Americans use cannabis, which is a significant increase from 2021 estimates of 6%, with about 33% of young adults between 18 and 25 years of age reported to be users.

The types and potency of currently available cannabis products have also increased. While Δ-9-tetrahydrocannabinol (THC), the primary psychoactive cannabinoid in cannabis, is present in dried cannabis flowers, the most common form in which cannabis has been smoked in the past, processed products are now widely available.

These processed products include hash, resin, kief (inhaled forms), shatter or wax (inhaled), liquid concentrates and dried herb (for vaping), concentrates infused into edibles like cookies and candies, drinks, or capsules, or into ointments, lotions, skin patches, and gels. Suppositories are also being sold.

The THC content of cannabis products has also increased by over 10%. Likewise, high-dose cannabis flowers exceeding 20% THC by weight have been sold at 50% higher volumes in one U.S. state in 2016 as compared to 2014. The sale of cannabis extracts containing triple the potency of THC than in flowers has also increased.

Cannabis in reproductive-age women

The prevalence of cannabis use during the past month reported among pregnant women in a 2014 National Survey on Drug Use and Health (NSDUH) increased by over 62% as compared to 2002, albeit at a very low frequency.

About 42% of North American cannabis users are women. The use of cannabis among pregnant women doubled from 3.5% to 7% in 2017 and 2002, respectively, with the highest use reported during the first trimester. About 4% of breastfeeding women were currently using cannabis.

Fewer women of reproductive age believe that cannabis use is dangerous, with many considering it medicinal, more effective, and less toxic than many medications, prescription or otherwise, for morning sickness. Lactating women often cite conditions like anxiety, depression, nausea, loss of appetite, chronic pain, and posttraumatic stress disorder as reasons for their cannabis use.

The fetus is exposed to maternally absorbed cannabis and its metabolites. Previous studies have shown a loss of verbal aptitude, attention, and short-term memory in fetuses exposed to cannabis in utero.

Cannabinoids in human milk

The effects of maternal cannabis use on lactation and the infant remain largely unknown. Cannabinoids appear in blood most rapidly after THC inhalation, rather than ingestion, at two to 10 minutes as compared to one hour, respectively.

Between 10-50% of total inhaled THC enters the plasma, most of which is bound to low-density lipoproteins (LDL) and reaches fat cells in multiple parts of the body. The small molecular weight of THC also allows it to enter and concentrate within fatty tissue, wherein it may accumulate at up to 104 times the plasma concentration.

The effect of body composition, which changes markedly during pregnancy and lactation, on circulating THC remains to be established.

The concentration of cannabinoids within milk varies with the time postpartum. During early lactation, drugs and proteins move easily from the blood into the milk through gaps between loosely packed epithelial cells. These gaps eventually narrow and utilize facilitated or passive diffusion to transfer molecules.

THC cannot return from milk into the maternal blood, thus leading to its sevenfold higher concentration in milk as compared to blood. Cannabis metabolites are stored within fat tissue and are slowly released during lactation into the milk.

THC is eventually metabolized in the liver into psychoactive metabolites like 11-OH-THC. The plasma levels of these molecules are higher than that of THC after smoking cannabis. However, both THC and its byproducts are broken down or inactivated, with only 6-7% of the ingested dose available to the body.

Most ingested cannabinoids eventually leave the body through feces, with about 20% being excreted through urine. The mean excretion time is 19 days.

Cannabinoids and breast epithelial cells

Several cannabinoid receptors exist in the endocannabinoid system (ECS), including the central nervous system, peripheral tissues/organs, and immune cells. Mammary epithelial cells (MECs) also contain cannabinoid receptors CB1R and CB2R, though at much lower concentrations than in cancerous cells.

Other receptors include CNR1 and CNR2 genes and peroxisome proliferator-activated receptors (PPARs). The latter regulates the transcription of target genes, which cause changes in cannabinoid metabolism and activate other cellular pathways. PPARA and PPARG are found at high levels in fat tissue and moderate levels in breast tissue, including MECs.

Several other membrane channel proteins can also transport cannabinoids across the cell membrane. Human mammary organoid research may be ideal to determine the effects of cannabinoids on mammary function.

Cannabinoids and milk composition

PPARγ expression rises in mammary tissue during lactation, thereby increasing lipid metabolism. The endocannabinoid AEA stimulates CB1R and PPARγ, ultimately increasing lipoprotein lipase activity. Prior research suggests that cannabinoids change human milk composition; however, no in vivo or clinical studies have corroborated this report.

Cannabinoids and milk production

Cannabinoids may initially increase prolactin (PRL) secretion through CB1R activation in the pituitary gland within the brain and eventually reduce PRL levels through dopamine release. Some rat research has shown that THC reduces PRL levels after lactation is established.

Human studies have been conflicting; however, some reports indicate lower milk production and shorter breastfeeding periods in women who regularly use cannabis.

Endocannabinoids may increase the latency period between suckling and oxytocin release in rats, which may inhibit milk ejection during breastfeeding. Increased dopamine release may also inhibit PRL secretion, whereas activation of the ECS may promote mother-infant bonding.

Conclusions

Cannabis use leads to the presence of cannabinoids in human milk, which may contribute to their long-term accumulation and inhibit milk production. Cannabis use may also alter breast milk composition through its effects on lipid metabolism.

Substantial research is needed utilizing rigorous methods for milk collection and production to demonstrate any of these potential effects.”

Future studies are needed to standardize milk production measurements, maternal adiposity characteristics, medication usage, time of day when milk collection is performed, and time since the last breastfeeding session and ensure accurate analysis.