"Most of the biochemical studies employed concentrations of Delta-9-THC that were in excess of physiologically meaningful concentrations that might be found in brain. In addition, the criterion of structure-activity relationship was not met -- that is, the potencies of the various cannabinoids in the in vitro assays did not correlate with their relative potencies in eliciting characteristic behavioral effects. Particularly damaging to the relevance of these in vitro studies was the absence of enantioselectivity."

Herkenham, M. (1992), "Cannabinoid Receptor Localization in Brain: Relationship to Motor and Reward Systems," P.W.Kalivas and H.H. Samson (eds.), The Neurobiology of Drug and Alcohol Addiction, Annals of the American Academy of Sciences. 654:19-32,1992. pg. 19.