Fig. 6.

Time course effects of the highest cumulative dose of each drug in warm-water tail-withdrawal tests, i.e., (1) 32 mg/kg morphine, (2) 1 mg/kg fentanyl, (3) 3.2 mg/kg beta-methylfentanyl, (4) 32 mg/kg para-methylfentanyl, (5) 10 mg/kg para-methoxyfentanyl, (6) 100 mg/kg fentanyl carbamate, (7) 10 mg/kg 3-furanylfentanyl, (8) 100 mg/kg phenylfentanyl, and (9) 100 mg/kg beta′-phenylfentanyl. Data are represented as curves determined by nonlinear regression with n = 8 mice per dose. Data for drugs (5) and (7) were modeled by identical curves and therefore are represented by a single line.