Randomized trials show that half-dose dual combination therapies for hypertension reduce blood pressure (BP) more than full-dose monotherapies, with no more adverse effects (1). Indeed, combining 2 drugs has an additive effect on BP reduction, whereas increasing the dose of a drug is less than additive (2): A half dose is only 25% less potent than a full dose. Under these assumptions, the expected potency of antihypertensive drug combinations can be approximated (Table). For example, the combination of 2 drugs at half dose is expected to be 50% more potent than a single drug at full dose. Using half doses ...