Long-term plasma monitoring of 38 children on Epidyolex for drug-resistant epilepsy confirmed that THC remained consistently undetectable while CBD levels rose predictably with dose.
Pediatric neurologists, parents of children on CBD therapy, pharmacokinetics researchers
THC was undetectable at every measurement in all 38 children over 5 years of CBD therapy
What the researchers found
THC was undetectable (<0.2 mcg/L) at all timepoints across all 38 patients throughout the study period (2019-2024). CBD plasma levels increased dose-dependently, reaching a median of 89.8 mcg/L at final follow-up, with a significant correlation between dose and concentration (p < 0.0001). Mean CBD dose was 13.6 mg/kg/day.
Why it matters
Parents of children on CBD therapy often worry about THC exposure. This long-term monitoring data provides strong reassurance that pharmaceutical-grade CBD (Epidyolex) produces no detectable THC in the blood, even over years of use, while confirming that dose adjustments reliably change CBD levels.
The numbers in context
THC undetectable (<0.2 mcg/L) at all timepoints; 38 patients; median age 11 years; mean CBD dose 13.6 mg/kg/day; median CBD level 89.8 mcg/L at final follow-up; significant dose-concentration correlation (p < 0.0001); 2019-2024 monitoring period
How the study worked
Retrospective analysis of 38 pediatric patients (median age 11 years) treated with Epidyolex at a single center from 2019 to 2024. Plasma CBD and THC measured using liquid chromatography-tandem mass spectrometry (LC-MS/MS).
What this study cannot tell us
Single center, retrospective design, only pharmaceutical-grade CBD studied (non-pharmaceutical products may differ), no clinical outcome data in this specific analysis, cannot generalize to adult patients
How to read the evidence
Moderate-sized retrospective monitoring study with objective laboratory measurements; strong pharmacokinetic data from a single center
When this study was published
Published 2025
The bigger picture
As CBD-based therapies expand, confirming long-term safety data like zero THC exposure is essential for both regulatory confidence and parental peace of mind. This study supports the case for therapeutic drug monitoring to optimize individual dosing.
Questions still open
- Do non-pharmaceutical CBD products produce similar zero-THC profiles? Would therapeutic drug monitoring improve seizure outcomes? Should plasma CBD monitoring become standard clinical practice?
Common questions
Does pharmaceutical CBD contain THC?
Do CBD blood levels change predictably with dose?
Read the original research
Long-term plasma monitoring of THC and CBD in pediatric drug-resistant epilepsy: Implications for cannabidiol therapy with Epidyolex®.
Epilepsia open, 10(5), 1699-1704
Citation
Cafaro, Alessia; Riva, Antonella; Pigliasco, Federica; Barco, Sebastiano; Manca, Valentina; Stella Vari, Maria; Mancardi, Maria Margherita; Nobili, Lino; Pichini, Simona; Busardò, Francesco Paolo; Striano, Pasquale; Cangemi, Giuliana. (2025). Long-term plasma monitoring of THC and CBD in pediatric drug-resistant epilepsy: Implications for cannabidiol therapy with Epidyolex®.. Epilepsia open, 10(5), 1699-1704. https://doi.org/10.1002/epi4.70112
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