Which statement must be true to conclude that the mechanism of antipsychotic effects for haloperidol, chlorpromazine, and clozapine is via binding to D2 receptors?

To conclude that the mechanism of antipsychotic effects for haloperidol, chlorpromazine, and clozapine is via binding to D2 receptors, it is essential to establish a relationship between drug affinity for D2 receptors and their antipsychotic potency. A positive correlation implies that as the affinity for D2 receptors increases, the potency in treating psychosis also increases. This connection provides a solid basis for asserting that the therapeutic effects of these antipsychotics are mediated through their action on D2 receptors.

Furthermore, examining the pharmacological profiles of these drugs reinforces this conclusion. Haloperidol and chlorpromazine are known for their dopamine antagonism, and their relative potencies can be understood in the context of their binding affinity to D2 receptors. If empirical data support the notion that increased D2 receptor binding correlates with greater efficacy in alleviating psychotic symptoms, it strengthens the hypothesis that the antipsychotic mechanism is indeed through these receptors.

In contrast, the other statements do not necessarily establish the required correlation between D2 receptor affinity and antipsychotic efficacy. They may suggest alternate pathways or relationships but do not directly affirm the critical link between D2 receptor binding and pharmacological action in a definitive manner.