The Parkinson trial scheduled comprehensive cognitive testing about one and a half hours after the final dose and plasma collection at three hours. Those observations were not simultaneous measurements of concentration and performance.
The protocol used distinct windows
Cannabinoids and metabolites were measured in plasma at initial and final dose visits, with collection three hours after administration. Comprehensive neuropsychological testing was scheduled at baseline and one and a half hours after the final dose.
Both belong to the same trial, but the timing needs to remain attached when discussing a concentration-related cognitive claim. A later plasma value is a sample of exposure at collection, not a direct measurement of an earlier brain concentration.
A time offset limits literal interpretation
Drug concentrations can change between an assessment and a specimen collection. Without an appropriate model or additional observations, the later value cannot simply be assigned to every moment of the earlier test. The offset itself does not establish the magnitude or direction of any resulting error.
What the measurements can support
The study documents exposure and clinical observations under a defined schedule. It does not establish a universal plasma concentration at which cognition changes or a method for back-calculating performance. Preserve the actual collection and task times, formulation and usual Parkinson medication context when comparing its findings with an individual case.
Related reading: exposure evidence and driving impairment.
Research cited
Liu and colleagues (2024). Short-term cannabidiol with delta-9-tetrahydrocannabinol in Parkinson disease: a randomized trial. DOI: 10.1002/mds.29768.
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