What does an antiadrenergic drug do?

An antiadrenergic drug primarily functions by blocking the receptors for norepinephrine or epinephrine, which are key hormones involved in the adrenergic response of the sympathetic nervous system. By inhibiting these receptors—specifically, the alpha and beta adrenergic receptors—antiadrenergic medications result in effects such as decreased heart rate, reduced blood pressure, and diminished energy expenditure. This makes them particularly useful in treating conditions like hypertension and certain cardiac conditions by counteracting the stimulatory effects of adrenaline on the heart and blood vessels.

The other options describe actions related to adrenergic activity rather than the blocking mechanism that characterizes antiadrenergic drugs. For instance, stimulating the fight or flight response refers to the activation of these receptors rather than their blockage. Similarly, increasing blood pressure and enhancing cardiac contractility are outcomes of adrenergic stimulation, opposite to what antiadrenergic drugs achieve.