Fenadiazole (INNTooltip International Nonproprietary Name), also known as phénadiazole (DCFTooltip Dénomination Commune Française)[1] and sold under the brand names Hypnazol, Eudormil, and Viodor, is a hypnotic and sedative medication which has been used to treat insomnia but is no longer marketed.

[2][3][4][5][6][7] It is described as a non-barbiturate hypnotic with marked or profound hypnotic and sedative properties in animals, variable hypnotic effects in humans (rapidly inducing sleep for 6 to 8 hours), additional anticonvulsant, antithermal, and spasmolytic effects, and a generally well-tolerated profile in humans (at an average dosage of 200 mg/day).

[7][8][9][10] The drug was synthesized, pharmacologically characterized, patented, and marketed by the French pharmaceutical company Laboratoires Jacques Logeais between 1960 and 1962.

[2][9][3][6] As a hypnotic and sedative, fenadiazole has a unique oxadiazole-based chemical structure.

[11] It may be chemically related to certain other hypnotics and sedatives with atypical chemical structures.