Human placenta perfusion studies confirm that P-glycoprotein and BCRP transporters actively pump THC back toward the mother, partially protecting the fetus from cannabis exposure — but some THC still gets through.
Pregnant cannabis users, OB-GYNs, placental biologists, and pharmacologists studying drug-transporter interactions
What the researchers found
A cocktail of P-gp and BCRP inhibitors significantly increased maternal-to-fetal THC transfer in perfused human placentas, confirming these transporters actively efflux THC and partially limit fetal exposure.
Why it matters
Understanding how the placenta handles THC explains why fetal exposure occurs but is limited — and why factors that compromise placental transporter function could increase fetal vulnerability.
The numbers in context
Inhibitor cocktail significantly increased unbound maternal-to-fetal THC clearance index compared to uninhibited controls; previous single-inhibitor (valspodar) failed to block efflux due to multiple transporter binding sites.
How the study worked
Ex vivo human placenta cotyledon perfusion with THC in the absence and presence of a cocktail of P-gp and BCRP inhibitors, measuring unbound maternal-to-fetal THC clearance index.
What this study cannot tell us
Ex vivo perfusion model has limited duration; does not capture chronic exposure effects; individual variation in transporter expression not assessed; does not measure THC metabolite transfer.
How to read the evidence
Direct human tissue experimentation with appropriate controls and building on prior work, but ex vivo model has inherent limitations.
When this study was published
Published in 2026, advancing understanding of placental THC handling with clinical implications.
The bigger picture
This reveals the placenta as an active gatekeeper against THC — but one that can be overwhelmed by high doses, genetic variants, or drug interactions that impair P-gp/BCRP function.
Questions still open
- Do genetic variations in P-gp/BCRP affect fetal THC exposure? Could medications that inhibit these transporters inadvertently increase fetal cannabis exposure?
Common questions
Does the placenta protect the baby from THC?
Can anything affect how much THC reaches the fetus?
Read the original research
Elucidating the role of ABC transporters in the placental efflux of (-)- Δ9-tetrahydrocannabinol (THC) using a cocktail of ABC transport inhibitors.
Placenta, 174, 174-177
Citation
Balhara, Ankit; Chen, Xin; Kumar, Aditya R; Wasickanin, Morgan E; Monson, Joshua W; Damicis, Jennifer R; Kinsman, Hillary J; Ieronimakis, Nicholas; Unadkat, Jashvant D. (2026). Elucidating the role of ABC transporters in the placental efflux of (-)- Δ9-tetrahydrocannabinol (THC) using a cocktail of ABC transport inhibitors.. Placenta, 174, 174-177. https://doi.org/10.1016/j.placenta.2025.12.012
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