CBD Crosses the Placenta and Dilates Fetal Blood Vessels While THC Constricts Them | Research

The takeaway

Using ex vivo human placental perfusion, researchers found that CBD transfers to the fetal side and dilates placental arteries via cannabinoid receptors, while THC causes constriction — revealing opposing vascular effects of the two most common cannabinoids during pregnancy.

Pregnant individuals using cannabis or CBD products, obstetricians, perinatal researchers, and pharmacologists studying cannabinoid placental transfer.

What the researchers found

CBD achieved a fetal/maternal ratio of 0.32 ± 0.23 and dilated healthy placental arteries by 36 ± 4% via CB1 and CB2 receptors, while THC induced vasoconstriction in the presence of CB1 receptor blockade — but CBD's rapid oxidation (>80% loss in 30 minutes) complicates in vivo predictions.

Why it matters

Many pregnant women use CBD products assuming safety, but this study shows CBD reaches the fetus and actively dilates fetal blood vessels — with unknown consequences for fetal development.

The numbers in context

CBD maternal concentration dropped >80% in 30 min from oxidation; fetal/maternal ratio 0.32 ± 0.23; 11 ± 4% recovered in tissue; CBD dilated arteries 36 ± 4%; dilation attenuated by AM251 and AM630; THC caused constriction with CB1 blockade

How the study worked

Ex vivo placental perfusion model using healthy term placentas with CBD quantification by LC-MS/MS, plus wire myography of chorionic plate arteries testing vascular reactivity of CBD and THC with CB1 (AM251) and CB2 (AM630) receptor antagonists.

What this study cannot tell us

Ex vivo model may not reflect in vivo conditions; rapid CBD oxidation required adding antioxidants that wouldn't be present naturally; healthy term placentas only; single-dose experiments; vascular effects measured in isolation from other placental functions.

How to read the evidence

Well-designed ex vivo study with receptor-specific pharmacology, but laboratory model may not accurately reflect in vivo placental transfer and oxidation dynamics.

When this study was published

Published 2026; uses current analytical methods for cannabinoid pharmacokinetics.

The bigger picture

The opposite vascular effects of CBD (dilation) and THC (constriction) on placental arteries suggest that different cannabis products may have very different effects on fetal blood supply during pregnancy.

Questions still open

Does CBD's vasodilatory effect benefit or harm the fetus? How much CBD reaches the fetus in real-world use accounting for oxidation? Could THC-induced vasoconstriction explain cannabis-associated fetal growth restriction?

Common questions

Does CBD cross the placenta to the baby?

Yes — this study showed CBD transfers from mother to fetus across the placenta, reaching about one-third of maternal concentration, though rapid oxidation may reduce actual fetal exposure in real-world use.

How do CBD and THC differently affect placental blood flow?

CBD dilated placental blood vessels by 36% through cannabinoid receptors, while THC caused constriction — suggesting these two cannabinoids have opposite effects on blood flow to the fetus.

Read the original research

Placental transfer and vasoactivity of cannabidiol: beware of rapid oxidation.

European journal of pharmacology, 1016, 178653

View on PubMed ↗Publisher’s paper ↗

Citation

Harhangi, M S; Höfert, L; Danser, A H J; Simons, S H P; Reiss, I K M; Baumann, S; Broekhuizen, M. (2026). Placental transfer and vasoactivity of cannabidiol: beware of rapid oxidation.. European journal of pharmacology, 1016, 178653. https://doi.org/10.1016/j.ejphar.2026.178653