LY-320,135 is a drug used in scientific research which acts as a selective antagonist of the cannabinoid receptor CB1. It was developed by Eli Lilly and Company in the 1990s.

LY-320,135 displays fairly good selectivity, with a binding affinity for CB1 around 70x stronger than for CB2,[1] but both its potency and selectivity are modest compared to newer agents, and at higher doses it also binds to a range of non-cannabinoid receptors. However LY-320,135 is still fairly widely used in research, particularly for elucidating the mechanisms by which many CB1 antagonists act as inverse agonists at higher doses.[2]