Stabilized composition of the tetrahydropyrrolo (1,2-a) pyrazine-4-spiro-3'-pyrrolidine.

A pharmaceutical composition comprising as an active ingredient (R) -2- (4-bromo-2-fluorobenzyl) -1, 2, 3, 4- tetrahydro-pyrrolo [1, 2-a] pyrazine-4-spiro-pyrrolidino-3? - 1 2?, 3, 5?-tetrone and as a stabilizer at least one acidic substance having a more potent than that of said active ingredient acidity.