CB1 PET Availability in Cannabis Users Was Not a Measure of Individual Impairment
A PET signal reflecting cannabinoid receptor availability is not an impairment score. A small comparison of chronic cannabis users and controls found lower CB1 availability in several brain regions, but did not establish how any individual would drive or perform after cannabis.
The study used a receptor-imaging tracer
Ten chronic cannabis users underwent imaging within the first week after their last reported consumption. Ten age-matched healthy participants served as controls. Researchers used the tracer fluorine-18 MK-9470 and calculated images intended to reflect cerebral CB1 availability.
The results were regional and comparative
The supplied abstract reports a global reduction in availability and significant regional differences in the temporal lobe, cingulate areas and nucleus accumbens. These are group imaging results rather than direct measurements of the amount of THC in blood.
Availability is an operational imaging measure
Tracer-based availability should not automatically be equated with an exact count of receptor proteins or permanent tissue damage. The interpretation depends on the tracer, imaging method, timing and biological factors affecting the signal.
The small observational comparison cannot independently isolate cannabis as the cause of every difference or establish a personal recovery timetable. It also did not validate an imaging cutoff for tolerance or impairment. The research supports investigation of neuroadaptation, while clinical and forensic conclusions still require evidence tied to the function and time period actually in question.
Related: interpreting cannabis tolerance claims.
Research cited
Ceccarini J; Kuepper R; Kemels D; van Os J; Henquet C; Van Laere K. [18F]MK-9470 PET measurement of cannabinoid CB1 receptor availability in chronic cannabis users. Addiction biology (2015). doi:10.1111/adb.12116. Findings discussed from the study abstract.
