Cyclothiazide (Anhydron, Acquirel, Doburil, Fluidil, Renazide, Tensodiural, Valmiran), sometimes abbreviated CTZ, is a benzothiadiazide (thiazide) diuretic and antihypertensive that was originally introduced in the United States in 1963 by Eli Lilly and was subsequently also marketed in Europe and Japan.

[1][2] Related drugs include diazoxide, hydrochlorothiazide, and chlorothiazide.

[3] In 1993, it was discovered that cyclothiazide is a positive allosteric modulator of the AMPA and kainate receptors, capable of reducing or essentially eliminating rapid desensitization of the former receptor, and potentiating AMPA-mediated glutamate currents by as much as 18-fold at the highest concentration tested (100 μM).

[3][4][5][6] Additionally, in 2003, cyclothiazide was also found to act as a GABAA receptor negative allosteric modulator, potently inhibiting GABAA-mediated currents.

[7] In animals it is a powerful convulsant, robustly enhancing epileptiform activity and inducing seizures, but without producing any apparent neuronal death.