Breastfeeding and Weed: Cannabis, Pregnancy and Breast Milk (2026)

By James Buddsey · Updated October 16, 2026

Major U.S. health bodies, including the CDC, FDA, ACOG and the American Academy of Pediatrics, advise against using cannabis while pregnant or breastfeeding, because THC passes into breast milk and crosses the placenta. Studies have found THC in most breast milk samples from mothers who use cannabis, sometimes up to about 6 days after use. Prenatal use is linked to lower birth weight, preterm birth and later attention and behavior problems, though the evidence is mostly observational.

This page began as a short news item about a striking finding: human breast milk naturally contains cannabinoid-like compounds. That finding is real, but it is often misread as proof that THC is safe for babies. It is not. This guide explains what the natural compounds are, what research shows about THC in milk and during pregnancy, and what doctors recommend, as of October 2026.

Cannabis, Pregnancy and Breastfeeding at a Glance

What “Cannabinoids in Breast Milk” Really Means

The body makes its own cannabinoid-like messengers, called endocannabinoids. The best known are anandamide and 2-AG. They act on the same CB1 receptors that THC activates, and a 2004 review in the European Journal of Pharmacology noted that they have been detected in maternal milk.

The research behind the old headline came from Israeli scientists, including cannabis research pioneer Raphael Mechoulam. In a 2001 study in the European Journal of Pharmacology, newborn mouse pups given a drug that blocks CB1 receptors stopped feeding properly, failed to grow and died within 4 to 8 days. The first 24 hours after birth were the most critical. The authors concluded that the endocannabinoid system plays a vital role in suckling and early growth in mice.

Three points are often lost in retellings:

• This was an animal study. It showed what happens when the system is blocked, not what happens when extra THC is added.
• Breast milk contains the body’s own endocannabinoids in natural amounts. It does not contain THC unless the mother uses cannabis.
• No study has shown that adding THC to milk helps babies feed or grow. The 2004 review floated cannabinoids as a possible future treatment for infant failure to thrive and cystic fibrosis, but more than 20 years later that idea remains unproven.

The finding is a good illustration of why the endocannabinoid system matters in early life. That same sensitivity is one reason researchers worry about outside cannabinoids reaching a developing brain. Our explainer on how THC affects the brain covers the receptor system in more detail.

Does THC Get Into Breast Milk?

Yes. THC is fat-soluble, and breast milk is rich in fat.

• In a 2018 University of California San Diego study of 54 milk samples from 50 breastfeeding women who used cannabis, THC was detectable in 34 samples (63%), up to about 6 days after last use. More daily uses meant higher levels.
• A 2018 pilot study of eight mothers who smoked a measured amount of high-THC cannabis found THC in milk at every time point tested over 4 hours. The authors estimated that an exclusively breastfed infant would take in about 2.5% of the mother’s dose on average, and up to 8.7%.

Those amounts are small, but no one knows what level is safe for a developing brain, and daily use means daily exposure. Because THC is stored in fat and released slowly, “pumping and dumping” after a single session does not reliably clear it, as the multi-day detection in the San Diego study shows.

Cannabis During Pregnancy: What the Research Shows

THC crosses the placenta. The question is what that exposure does. Most of the evidence comes from observational studies, which compare pregnancies with and without cannabis use and try to adjust for tobacco, alcohol, income and other factors. They cannot prove cause and effect.

Birth outcomes

A 2024 systematic review and meta-analysis of 53 studies, led by researchers at Oregon Health and Science University, found cannabis use during pregnancy was associated with higher odds of preterm birth (adjusted odds ratio 1.42), babies small for gestational age (1.76) and perinatal death (1.5), even after accounting for tobacco. The authors rated the certainty as very low to low, mainly because most studies did not record how much or when women used cannabis. The CDC says prenatal cannabis use may cause lower birth weight and abnormal neurological development, and the National Academies found substantial evidence linking maternal cannabis smoking to lower birth weight.

Childhood development

The large U.S. Adolescent Brain Cognitive Development study looked at more than 11,000 children aged 9 to 11. In a 2021 analysis in JAMA Psychiatry, children whose mothers kept using cannabis after learning they were pregnant had more attention, behavior, thought and social problems and more psychotic-like experiences, even after adjusting for many family factors. Use only before the mother knew she was pregnant was not linked to differences after adjustment. The study was cross-sectional and relied on mothers’ recall, so it shows association, not proof.

An older study on infant deaths

A 1997 Detroit study in Pediatrics screened 2,964 newborns for drug exposure using meconium, the baby’s first stool. About 11% tested positive for cannabinoids. Drug-exposed babies were smaller at birth, but the study did not find an overall rise in deaths or SIDS in the first two years. This single study mixed cannabis with cocaine and opioid exposure and was too small to detect modest differences. The newer meta-analysis above, which pools far more births, does find a link between cannabis and perinatal death, though with low certainty.

Morning Sickness and Cannabis

Many pregnant people try cannabis for nausea, and some dispensaries encourage it. When researchers called 400 Colorado dispensaries posing as a woman 8 weeks pregnant with morning sickness, nearly 70% recommended a cannabis product, and 36% said it was safe in pregnancy, mostly based on personal opinion. Few suggested talking to a doctor without being asked.

The American College of Obstetricians and Gynecologists says doctors should not suggest cannabis during preconception, pregnancy or breastfeeding, and that patients using it for medical reasons should switch to treatments with better pregnancy safety data. Safer, studied options for nausea exist. Heavy cannabis use can also cause cannabinoid hyperemesis syndrome, a cycle of severe vomiting that can be mistaken for severe morning sickness.

What About CBD?

CBD is not a safe workaround. The FDA strongly advises against CBD, THC and marijuana in any form during pregnancy and breastfeeding. It notes that high doses of CBD affected reproductive development in male offspring of pregnant test animals, that some CBD is expected to pass into breast milk, and that products may be contaminated or contain THC. The CDC says the effects of CBD during pregnancy are unknown. See our CBD evidence guide for what CBD has and has not been shown to do.

Evidence at a Glance

Risks and Side Effects

• For the baby during pregnancy: associations with lower birth weight, preterm birth, being small for gestational age and later attention and behavior problems.
• For the breastfed baby: repeated exposure to THC of unknown long-term effect, and secondhand smoke if anyone smokes nearby.
• For the parent: impairment while caring for an infant, unsafe sleep if a high parent falls asleep with the baby, cannabis use disorder and hyperemesis.
• Edibles at home: accidental poisoning of toddlers and older siblings. Store all cannabis locked and out of reach.

Hospitals may test newborns or mothers for drugs, and a positive result can lead to a child welfare referral in some states even where cannabis is legal. Policies vary, so ask your provider how yours handles it.

Talk to Your Doctor

If you use cannabis and are pregnant, trying to conceive or breastfeeding, tell your obstetrician, midwife or pediatrician. You will not be judged for being honest, and they need to know to give good advice. Ask about safer treatments for nausea, anxiety, pain or sleep. If you use daily and find it hard to stop, ask about support; our guide to treatment options explains what works. Breastfeeding has well-established benefits, so the goal is usually to stop cannabis, not to give up nursing without talking it through. The American Academy of Pediatrics’ 2018 clinical report covers what pediatricians are advised to tell families.

Breastfeeding and Weed FAQ

More research in our cannabis research section.

For adults 21+ in legal states. General information, not medical advice. Talk to a doctor before using cannabis for a health condition.