Report on progress in the Australian National Blood Pressure Study (NBPS)

1. The National Blood Pressure Study (NBPS) is a single blind trial designed to test the efficacy of active drug treatment in reducing complications from mild hypertension (mean diastolic pressure = 95-109 mmHg). 2. Between 1973 and 1975, four centres screened about 104 000 subjects aged 30-69 years, yielding an estimated prevalence of hypertension (greater than or equal to 95 mmHg diastolic) of 16% and of moderate-to-severe hypertension (greater than of equal to 110 mmHg diastolic) of 1-3%. 3. Some 4000 subjects selected for untreated uncomplicated mild hypertension were randomized to either active treatment (cholorothiazide +alpha-methyldopa and/or a beta-adrenoreceptor antagonist as required) or to matching placebos. 4. At 1 year mean pressures had fallen significantly below entry pressures in both groups but in the active group the fall was greater by a margin of 14-4+/-1-3 (SEM) mmHg systolic and 7-1+/-0-7 mmHg diastolic. At 1 year 5% of subjects in the placebo group had been placed on active treatment on the ethical grounds that pressure had exceeded the mild hypertension limit. 5. Trial end-points (death, morbidity from stroke, hypertensive heart and renal disease, and ischaemic heart disease) number 106 (nine deaths) thus far, of which ischaemic heart disease accounts for 71% and stroke 19%. 6. The duration of trial may need to be extended beyond the original estimate of 5 years.