Published THC Receptor-Affinity Values Varied Across the Same Review’s Table

A cannabinoid review reported multiple receptor-affinity estimates for THC rather than one universal value. Selecting a single number without its experimental source can make a comparison appear more precise than the underlying evidence supports.

The table preserved separate estimates

Heal and colleagues assembled published CB1 and CB2 affinity values for naturally occurring and synthetic cannabinoids. Their table contains several estimates for delta-9 THC and repeated entries for other compounds. They explicitly describe it as a collection illustrating categories and the spread of reported values, rather than an exhaustive or standardized ranking.

Binding and functional response remain different

Affinity estimates describe a compound’s interaction with a receptor in a particular experimental system. The review separately presents functional measures, including concentrations associated with a response and maximal effects. A strong binding interaction does not supply every piece of information about receptor activation, tissue exposure or behavior.

Comparisons need compatible experimental context

A ratio assembled from two different publications may combine differences in preparation and measurement with differences between the compounds themselves. The review’s spread of estimates is a reason to retain that uncertainty. It does not show which laboratory result is wrong, and the table alone cannot quantify how much any particular methodological factor contributed.

What the numbers cannot establish

These in-vitro measurements are not blood or oral-fluid impairment thresholds. They cannot establish that a product is a specified number of times more intoxicating in a person. A defensible interpretation identifies the receptor, measurement and source before making a comparison, then distinguishes that laboratory comparison from the separate questions of exposure, clinical response and individual functioning.

Related analysis: compound-specific cannabinoid risk assessment.

Research cited

This analysis uses the research synthesis in Heal DJ, Gosden J and Smith SL (2024), A critical assessment of the abuse, dependence and associated safety risks of naturally occurring and synthetic cannabinoids, Frontiers in Psychiatry.