An atypical antipsychotic drug composition is disclosed, which comprises a mixture of: (i) a drug selected from the group consisting of quetiapine fumarate or quetiapine hydrochloride； (ii) an organic acid selected from the group consisting of succinic acid and a mixture of succinic and fumaric acid； and (iii) at least one pharmaceutically acceptable excipient, wherein the pH of a 1 % weight by volume solution or suspension of the composition in purified water is less than 5 and the ratio of quetiapine fumarate or quetiapine hydrochloride to the organic acid is about 1:3 to about 3:1.
