The Medical Research Council Trial.

THE medical literature over the past half dozen or more years has been strewn with reports and commentaries on the treatment of mild hypertension. Those who are particularly influenced by the evidence from the insurance companies point to the well-documented increased mortality in the presence of even a little high blood pressure, cite the efficacy of lowering blood pressure by various nonpharmacological and pharmacological means, and urge public education and individual and mass intervention. Others, though not doubting the actuarial data, have not been reluctant to express different views; they have pointed to the limitations of and uncertainties in the findings from the various clinical trials to date and said, "Go slow." Characteristic of the contrary stands are the comments by Frohlich: "We should still consider that all individuals whose diastolic blood pressure exceeds 90 mm Hg are at increased cardiovascular risk. Moreover, we must still recognize that in these individuals pressure should be reduced in order to minimize that risk." And the comments by Kaplan: "We must not lose sight of the admonition that therapy of asymptomatic hypertension is preventive therapy, not curative. Further, only a minority of hypertensive patients will be saved from disease and death by such therapy. We should do nothing that will add any degree of risk, be it ever so small, to the large majority of mild hypertensive patients who would not suffer if left untreated." It was hoped that the results of the recent Medical Research Council (MRC) Trial might at least partially resolve the controversy. In brief, the MRC Trial was a clinical trial of drug treatment of mild hypertension (baseline systolic pressure less than 100 mm Hg; diastolic pressure, 90-109 mm Hg). The trial included 17,354 subjects aged 35 to 64 years who were observed for an average of 5'/2 years. Nearly all were white, and the division between the sexes was almost equal. Most of these participants were members of general practice clinics mainly located in small towns. Excluded were patients already receiving antihypertensive treatment, those known to have diabetes, gout, asthma, angina pectoris, or intermittent claudication, and those who had experienced a recent myocardial infarction or stroke. The trial, which was single blind, provided for random allocation of the participants to four schedules: treatment with a fixed dose (10 mg daily) of a thiazide diuretic (bendrofluazide) or a similar looking placebo, and treatment with graded daily doses up to 240 mg of a /3-blocking drug (propranolol) or a similar appearing placebo. No specific advice was given regarding salt intake, obesity, exercise, or smoking. Treatment with active drugs resulted in substantial drops in blood pressure that were