The main question was that if in patients with hypertension, what is the efficacy of a calcium channel blocker, ACE inhibitor, or thiazide diuretic in lowering the incidence of CV events? This trial randomized 33, 357 patients to either get chlorthalidone, amlodipine, or lisinopril for blood pressure control. There were an additional 9061 patients they were randomized to doxazosin but this arm was stopped early due to evidence of increased harm. The primary outcome was combined fatal coronary heart disease or nonfatal myocardial infarction. The main outcome was that there is no significant difference between the primary outcome for Lisinopril, chlorthalidone, or amlodipine. The main question for this study was a pretty timely one. At the time of the study, calcium channel blockers and ACE inhibitors were newer and more expensive than chlorthalidone. Pfizer had patent protection on amlodipine until 2007. Patent protection for Lisinopril lasted until June of 2002. What this study contributes overall to medical knowledge was that the more expensive medications of amlodipine and lisinopril at that time were no better than the more cost-effective chlorthalidone.
The ALLHAT Trial: Furberg, C. D., Wright, J. T., Davis, B. R., Cutler, J. A., Alderman, M., Black, H., ... & Oparil, S. (2002). Major outcomes in high-risk hypertensive patients randomized to angiotensin-converting enzyme inhibitor or calcium channel blocker vs diuretic: the Antihypertensive and Lipid-Lowering Treatment to Prevent Heart Attack Trial (ALLHAT). Journal of the American Medical Association, 288(23), 2981-2997.
ALLHAT PMID: 12479763
Useful summaries of the ALLHAT Trial: Wiki Journal Club