Hypertension is a risk factor for atherosclerosis, heart failure, coronary artery disease, stroke, renal disease, and peripheral arterial disease, and is the most important risk factor for cardiovascular morbidity and mortality, in industrialized countries. Prior to 1940 approximately 23% of all deaths among persons over age 50 were attributed to hypertension. Severe cases of hypertension were treated by surgery.
Early developments in the field of treating hypertension included quaternary ammonium ion sympathetic nervous system blocking agents, but these compounds were never widely used due to their severe side effects, because the long-term health consequences of high blood pressure had not yet been established, and because they had to be administered by injection.
In 1952 researchers at Ciba discovered the first orally available vasodilator, hydralazine.  A major shortcoming of hydralazine monotherapy was that it lost its effectiveness over time (tachyphylaxis).  In the mid-1950s Karl H. Beyer, James M. Sprague, John E. Baer, and Frederick C. Novello of Merck and Co. discovered and developed chlorothiazide, which remains the most widely used antihypertensive drug today. This development was associated with a substantial decline in the mortality rate among people with hypertension. The inventors were recognized by a Public Health Lasker Award in 1975 for "the saving of untold thousands of lives and the alleviation of the suffering of millions of victims of hypertension".
A 2009 Cochrane review concluded that thiazide antihypertensive drugs reduce the risk of death (RR 0.89), stroke (RR 0.63), coronary heart disease (RR 0.84), and cardiovascular events (RR 0.70) in people with high blood pressure. In the ensuring years other classes of antihypertensive drug were developed and found wide acceptance in combination therapy, including loop diuretics (Lasix/furosemide, Hoechst Pharmaceuticals, 1963), beta blockers (ICI Pharmaceuticals, 1964) ACE inhibitors, and angiotensin receptor blockers. ACE inhibitors reduce the risk of new onset kidney disease [RR 0.71] and death [RR 0.84] in diabetic patients, irrespective of whether they have hypertension.