Fig. 6. Three examples of the concentration–effect relation predicted by the pharmacodynamic model f(x) = E⁰(1 − x^γ), where x^γ= U^γ/2 and U = C/C⁵⁰, obtained at three fixed values of γ (0.2, 1, and 4). When γ= 1, the model becomes linear. At all three γ values, negative effects are possible at drug concentrations x > C⁵⁰· 2^1/γ. Note that the values for C⁵⁰and γ were chosen in such a way that the zero crossing for all three examples occurred at the same value of C. As a consequence, the values of C causing 50% of the effect (i.e. , C⁵⁰) occur at different values of C (C¹through C³are the C⁵⁰values for the three different curves). Different values for C⁵⁰and γ would result in the zero crossing at different values of C. E⁰= baseline effect; E⁵⁰= 50% depression of effect.