Lysergic acid 2,4-dimethylazetidide (LA-SS-Az, LSZ) is an analog of LSD developed by the team led by David E. Nichols at Purdue University. It was developed as a rigid analog of LSD with the diethylamide group constrained into an azetidine ring in order to map the binding site at the 5-HT2A receptor. There are three possible stereoisomers around the azetidine ring, with the (S,S)-(+) isomer being the most active, slightly more potent than LSD itself in drug discrimination tests using trained rats.