Tasimelteon (BMS-214778) has 2.1-4.4 times greater affinity for the MT2 receptor believed to mediate circadian rhythm phase-shifting (K i =0.0692 nM and K i =0.17 nM in NIH-3T3 and CHO-K1 cells, respectively), than for the MT1 receptor (Ki=0.304 nM and Ki=0.35 nM, respectively). Tasimelteon has no appreciable affinity for more than 160 other pharmacologically relevant receptors and several enzymes.