It was the largest and most important investigation of treatments for high blood pressure ever conducted, with a monumental price tag to match. U.S. doctors enrolled 42,418 patients from 623 offices and clinics, treated participants with one of four commonly prescribed drugs, and followed them for at least five years to see how well the medications controlled their blood pressure and reduced the risk of heart attack, stroke and other cardiovascular problems. It met the highest standards of medical research: neither physicians nor their patients knew who was placed in which treatment group, and patients had an equal chance of being assigned to any of the groups. Such randomized controlled trials have long been unmatched as a way to determine the safety and efficacy of drugs and other treatments. This one, dubbed ALLHAT (Antihypertensive and Lipid-Lowering Treatment to Prevent Heart Attack Trial), cost an estimated $120 million and took eight years to complete.