Cannabis during pregnancy and breastfeeding: Risks
Cannabis is considered “natural” — and precisely for this reason, some pregnant women underestimate the risk. In fact, cannabis during pregnancy is one of the few topics where scientific…
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Cannabis is considered “natural” — and precisely for this reason, some pregnant women underestimate the risk. In fact, cannabis during pregnancy is one of the few topics where scientific evidence is clear and consistent: THC reaches the fetus directly and can permanently influence brain development.
Why THC is particularly risky for fetuses
The endocannabinoid system (ECS) plays a central role in fetal development — long before birth:
- ECS in fetal development: CB1 and CB2 receptors are already active in early embryonic development (from 5th to 6th week of pregnancy). Endocannabinoids regulate neuron migration, synapse formation, and cortical maturation
- THC as a disruptive factor: THC mimics anandamide and interferes with these developmental signals. In animal models, prenatal application of THC permanently disrupts correct neuron migration and synaptogenesis
- Sensitive window: The first trimester is particularly critical — during this phase, fundamental brain architectures are established. However, the second and third trimesters are also not safe — neuronal pruning and myelination continue well beyond birth
THC Transfer: Placenta and Breast Milk
THC is lipophilic — it crosses biological barriers with particular efficiency:
- Placental transfer: THC crosses the placental barrier. Studies show detection of THC in fetal blood in consuming mothers. The placental concentration is approximately 10–30% of the maternal plasma concentration
- Breast milk: THC accumulates in breast milk — due to its lipophilic nature, resulting in higher concentrations than in plasma. Studies (Eidelman & Baker 2016, Bertrand 2018) show detection of THC in breast milk from consuming mothers even days to weeks after the last consumption
- Infant exposure: A breastfed child takes up about 0.8% of the mother’s THC dose through breast milk — sounds low, but the weight ratio makes the difference: A 5-kg infant receives significantly more THC per kg of body weight than the mother
- CBD: CBD also crosses the placenta and enters breast milk — safety data for CBD during pregnancy are still insufficient, so it is not recommended either
Documented Risks for the Child
Epidemiological studies show consistent findings:
- Birth weight: Prenatal cannabis use is associated with an increased risk of low birth weight (under 2500 g) and preterm birth — several meta-analyses confirm this
- Neurocognitive development: ABCD Study (Adolescent Brain Cognitive Development, n>11,000): Children exposed to cannabis prenatally show significantly worse cognitive test results, more behavioral problems, and higher rates of anxiety disorders and ADHD symptoms at the age of 9–10 years
- Ottawa Prenatal Prospective Study: Long-term follow-up (30+ years): Prenatal cannabis exposure correlates with poorer school performance, attention problems, and increased risk of substance use in adulthood
- Sleep architecture in newborns: Studies show altered sleep patterns in newborns of mothers who use cannabis — ECS dysregulation as a possible mechanism
Common Misconceptions
Why cannabis is consumed during pregnancy despite the risks:
- “Natural = safe”: Natural origin does not mean a safety certificate. Alcohol and nicotine are also “natural” and highly risky during pregnancy
- “Against nausea in pregnancy”: Increasingly common in the US — cannabis for hyperemesis gravidarum. Evidence of effectiveness is lacking, and fetal risk is documented. Medically approved antiemetics (ondansetron, promethazine) are safer
- “Occasional use is okay”: There is no safe threshold for prenatal cannabis use. The first trimester is particularly critical, but no point during pregnancy is “safe”
- “CBD is safe”: CBD safety data during pregnancy are insufficient. The WHO and EMA explicitly do not recommend CBD during pregnancy
Recommendations and Alternatives
- Complete abstinence: All medical societies (WHO, ACOG, DGGG) recommend complete cannabis abstinence during pregnancy and breastfeeding
- Nausea during pregnancy: Ginger (1 g/day, evidence-based), vitamin B6, acupressure wristbands, and approved antiemetics under medical supervision in severe cases
- Anxiety/sleep during pregnancy: Progressive muscle relaxation, pregnancy yoga, cognitive behavioral therapy — without pharmaceutical interventions
- If currently used: Immediate need for a conversation with a gynecologist — no judgment, but support. Many practices have experience with this conversation
How THC enters and is broken down in the body — basics: