MRK-409, also known as MK-0343, is a GABAA receptor partial agonist.

[2] It was designed to be a non-sedative anxiolytic, however its development was halted because it produced sedation in humans.

[3] Despite lacking the benzodiazepine chemical structure, MRK-409 acts on the benzodiazepine binding site, it is therefore a nonbenzodiazepine.

MRK-409 binds to the α1, α2, α3 and α5 subunits of the GABAA receptor.

[4] In rats, it produces minimal to no sedation, however it produces sedation in humans at doses above 1 mg.[3][5]