For years, the honest answer to “Is it okay to use cannabis while breastfeeding?” has been a frustrating shrug. Scientists knew THC crosses into breast milk. What they didn’t know was whether the other passengers in cannabis smoke — the harsh, industrial-sounding chemicals that also ride along in a burning joint — end up inside the baby. A new study set out to check the most direct place possible: the diaper.
Researchers at Washington State University, working with the U.S. Centers for Disease Control and Prevention, collected urine from exclusively breastfed infants whose mothers use cannabis and screened it for a family of compounds called volatile organic compounds, or VOCs. The results, published on 15 July 2026 in the International Journal of Environmental Research and Public Health as part of the Lactation and Cannabis (LAC) Study, are the first of their kind — and they’re more nuanced than either the alarmist or the “it’s totally fine” camp will want them to be.
Key Takeaways
Here’s the short version before we dig in. Scientists detected 24 different smoke-related chemical byproducts in the urine of breastfed babies whose mothers use cannabis, and levels of many of them rose after mom used cannabis compared with a baseline taken after twelve hours of not using. Two of those byproducts come from known carcinogens — acrylonitrile and acrylamide, the same compounds found in cigarette smoke — and their levels tracked closely with how much THC was in the mother’s milk. Crucially, babies whose mothers smoked had noticeably higher levels than babies whose mothers only vaped. But before anyone panics, two things matter enormously: the study was tiny (fewer than twenty mother–infant pairs), and the amounts measured in these infants were actually lower than the U.S. average for older children. The researchers are explicit that no conclusions about safety or harm can be drawn yet. This is a first flare fired into a dark room, not a verdict.
What the Researchers Actually Did
The setup was clever in its simplicity. Twenty breastfeeding mothers in Washington and Oregon, all frequent cannabis users with infants under six months old, took part. On a study day, each mother first gave a “clean” baseline: a milk sample and an infant urine sample collected after at least twelve hours without any cannabis. Then she used cannabis exactly the way she normally would — her own product, her own method, no researcher-supplied joints — and over the next eight to twelve hours collected several more milk and urine samples.
Collecting urine from an infant is not glamorous science. Mothers lined fresh diapers with sterile cotton balls, checked them constantly, and squeezed the results into tiny tubes that went straight into the home freezer before being shipped on ice to a CDC lab. In the end, 65 infant urine samples from 19 mother–infant pairs made it through quality control and into the analysis.
The Chemicals Nobody Wants in a Nursery
Using highly sensitive mass spectrometry, the lab found detectable levels of 24 out of 32 VOC metabolites they screened for. Fifteen of them showed up at higher concentrations after the mother used cannabis than in the clean baseline sample. Every single infant had at least one urine sample with detectable VOC byproducts, which tells us that early-life exposure to these compounds is simply a fact of the modern environment.
Two metabolites became the center of attention. The first, nicknamed 2CyEMA, is what your body produces after exposure to acrylonitrile — a carcinogen used to make plastics and synthetic rubber, and a known component of tobacco smoke. The second, 2CaEMA, is the fingerprint of acrylamide, another carcinogen found in cigarette smoke (and, oddly, in browned foods like fries and toast). Both of these rose in the infants’ urine after maternal cannabis use, and both climbed in step with the amount of THC measured in the mother’s milk. In statistical terms, the more THC in the milk, the more of these carcinogen byproducts in the baby.
Smoking Versus Vaping: Where the Difference Shows Up
This is the finding with the clearest real-world takeaway. Infants of mothers who smoked cannabis on the study day had roughly 89% higher average levels of the acrylonitrile byproduct than infants of mothers who only vaped. The acrylamide byproduct followed the same pattern.
The chemistry behind this makes intuitive sense. Combustion — actually burning plant material — reaches much higher temperatures than vaporizing does, and it’s that heat that forges compounds like acrylonitrile and acrylamide in the first place. Vaping heats cannabis below the threshold where a lot of these nasties are created, so less of them end up in the inhaled aerosol, in the bloodstream, and, apparently, in the baby. It’s a pattern researchers have seen before with tobacco, and it fits neatly into the broader picture of how consumers increasingly mix smoking, vaping and other methods, each of which carries its own chemical signature. That said, the vaping group here was tiny — only two mothers vaped exclusively — so this comparison, while striking, rests on thin data.
The Context That the Headlines Will Skip
Now for the part that keeps this study honest. When the researchers compared their infants’ VOC levels against national reference data from the CDC’s exposure survey, they found something reassuring: for the majority of the 32 compounds measured, the U.S. average for children aged three to five was at least 40% higher than in these breastfed infants. In other words, the babies in this study were not swimming in a chemical soup relative to the general population of young children. Their exposure was real but, by this imperfect yardstick, on the low end.
It’s also worth remembering why so many new mothers reach for cannabis in the first place. The postpartum months bring pain, exhaustion, anxiety and sleeplessness, and cannabis has been widely — if not always accurately — perceived as a low-risk way to cope. That perception is part of what’s driving rising use during lactation, and it’s why growing numbers of adults now turn to cannabis for sleep and stress relief. Understanding the trade-offs, rather than just issuing blanket warnings, is exactly what studies like this are meant to enable.
What This Study Does Not Tell Us
The authors deserve credit for how loudly they flag their own limits, and any honest write-up has to echo them. First, the original LAC Study was never designed to measure VOC exposure, so the team couldn’t rule out other sources — household smoke from other people, thirdhand residue on surfaces, or even the infant’s own diet. A baby’s urine can’t say whether a chemical arrived through breast milk, through the air, or off a couch cushion.
Second, there was no comparison group of infants whose mothers don’t use cannabis, which makes it impossible to isolate cannabis as the driver with certainty. Third, the sample was small and the mothers used wildly different products at wildly different doses, so nothing here can be standardized into a neat “X amount of cannabis equals Y risk” formula. And fourth — the big one — nobody knows what these particular doses actually do to a developing infant. Acrylonitrile and acrylamide are linked to cancer in adults after long-term exposure; the health meaning of the trace amounts seen here, at this stage of life, is genuinely unknown.
The distinction between combustion and vaporization that runs through the results also reflects a wider shift in how people consume the plant, from inhaled and vaporized forms to edibles and beverages — a shift that will shape what future exposure studies need to measure.
So What Should Parents Take From This?
Not a scare, and not a green light. What this study offers is a first, credible piece of evidence that the chemicals of cannabis smoke — not just its THC — can reach a breastfed baby, and that the delivery method matters. For a mother weighing her options, the smoking-versus-vaping gap is a concrete, actionable data point, even if the science underneath it is still young.
Major health bodies, including the U.S. FDA, CDC, the American Academy of Pediatrics and the American College of Obstetricians and Gynecologists, currently advise against cannabis use during breastfeeding, citing THC transfer and unknowns exactly like the ones this study probes. That guidance predates this paper and isn’t changed by it. What has changed is that the “unknown VOCs” box on the risk chart now has real numbers in it — small numbers, but numbers — and a clear next step: bigger studies, with control groups, that can finally say whether any of this matters for a child’s long-term health.
Frequently Asked Questions
No, and the authors are emphatic about that. It proves only that measurable smoke-related chemicals can be detected in these infants and that some of them rise after maternal cannabis use. Whether those amounts cause any harm is unknown, and the study had no way to prove cannabis was the sole source. It’s a starting point for research, not a health verdict.
The study found lower levels of two carcinogen byproducts in babies whose mothers vaped rather than smoked, which fits the chemistry of lower-temperature vaporization. But “lower” is not “safe” — THC itself still transfers into milk regardless of method, and the vaping group was extremely small. It’s a meaningful signal, not a clean bill of health for vaping.
Federal agencies and pediatric bodies uniformly advise against any cannabis use — including CBD — during breastfeeding, based on THC transfer and a lack of safety data. Note that this is medical guidance, not a criminal prohibition on nursing; the legal status of cannabis itself varies by state, and possession or use remains regulated differently across the U.S. Anyone making decisions here should talk to their own clinician about their specific situation.
In this study, each infant’s estimated average daily THC intake through breast milk ranged from about 0.002 to 0.196 milligrams per day, with an average near 0.05 milligrams. These are small quantities, but researchers caution that the long-term significance of even low, repeated exposure during early development has not been established.
Disclaimer
This article is provided for general informational and educational purposes only and reflects the findings of a single, early-stage scientific study. It is not medical advice and should not be used to make decisions about cannabis use, breastfeeding, or infant care. The research described involved a small sample and cannot establish cause, effect, or safety. Individuals who are pregnant, breastfeeding, or caring for an infant should consult a qualified healthcare professional about their specific circumstances. Laws governing cannabis differ by jurisdiction and change over time.
