Which of the following terms best describes a drug that blocks the action of adrenaline at its receptors by occupying those receptors without activating them?

* Pharmacological antagonist bind to same receptor and thus blocks the action of the drug e.g. atenolol (a beta receptor antagonist) is pharmacological antagonist of adrenaline. * Physiological antagonist binds to different receptor and produce opposite effect e.g. adrenaline produce bronchodilation by binding to beta 2 receptors whereas histamine cause bronchoconstriction by acting on H1 receptors. Thus adrenaline is physiological antagonist of histamine.