AM-2389 is a classical cannabinoid derivative which acts as a potent and reasonably selective agonist for the CB<sub>1</sub> receptor, with a K<sub>i</sub> of 0.16 nM, and 26ÃÂ selectivity over the related CB<sub>2</sub> receptor. It has high potency in animal tests of cannabinoid activity, and a medium duration of action. Replacing the 1',1'-dimethyl substitution of the dimethylheptyl side chain of classical cannabinoids with cyclopropyl or cyclopentyl results in higher potency than cyclobutyl, but only the cyclobutyl derivatives show selectivity for CB<sub>1</sub> over CB<sub>2</sub>. High selectivity for CB<sub>1</sub> over CB<sub>2</sub> is difficult to achieve (cf. AM-906, AM-1235), as almost all commonly used CB<sub>1</sub> agonists have similar or greater affinity for CB<sub>2</sub> than CB<sub>1</sub>, and the only truly highly selective CB<sub>1</sub> agonists known as of 2012 are eicosanoid derivatives such as O-1812.