Tolerance to behavioral effects of haloperidol

Haloperidol was given daily (3 mg/kg, i.p.) for 5 months. Catalepsy and ptosis in response to a single dose of the neuroleptic were measured weekly. Total scores of both responses gradually decreased, indicating the development of tolerance, but with different time courses. Ptosis and catalepsy responses became half of their initial values by approximately 5 and 10 weeks, respectively. In contrast, the $\text{onset}$ of these behavioral responses gradually became more rapid after each dose of haloperidol over the first 3 to 4 months.