Angiotensin-converting-enzyme (ACE) inhibitors have been used for more than a decade to treat high blood pressure, despite the lack of data from randomised intervention trials to show that such treatment affects cardiovascular morbidity and mortality. The Captopril Prevention Project (CAPPP) is a randomised intervention trial to compare the effects of ACE inhibition and conventional therapy on cardiovascular morbidity and mortality in patients with hypertension. CAPPP was a prospective, randomised, open trial with blinded endpoint evaluation. 10 985 patients were enrolled at 536 health centres in Sweden and Finland. Patients aged 25–66 years with a measured diastolic blood pressure of 100 mm Hg or more on two occasions were randomly assigned captopril or conventional antihypertensive treatment (diuretics, β-blockers). Analysis was by intention-to-treat. The primary endpoint was a composite of fatal and non-fatal myocardial infarction, stroke, and other cardiovascular deaths. Of 5492 patients assigned captopril and 5493 assigned conventional therapy, 14 and 13, respectively, were lost to follow-up. Primary endpoint events occurred in 363 patients in the captopril group (11·1 per 1000 patient-years) and 335 in the conventional-treatment group (10·2 per 1000 patient-years; relative risk 1·05 [95% Cl 0·90–1·22], p=0·52). Cardiovascular mortality was lower with captopril than with conventional treatment (76 vs 95 events; relative risk 0·77 [0·57–1·04], p=0·092), the rate of fatal and non-fatal myocardial infarction was similar (162 vs 161), but fatal and non-fatal stroke was more common with captopril (189 vs 148; 1·25 [1·01–1·55]. p=0·044). Captopril and conventional treatment did not differ in efficacy in preventing cardiovascular morbidity and mortality. The difference in stroke risk is probably due to the lower levels of blood pressure obtained initially in previously treated patients randomised to conventional therapy.
