The Minimal Impact of a Big Hypertension Study.

    The surprising news made headlines in December 2002. Generic pills for high blood pressure, which had been in use since the 1950s and cost only pennies a day, worked better than newer drugs that were up to 20 times as expensive.

    Briana Brough for The New York Times

    "The pharmaceutical industry ganged up and attacked, discredited the findings," said Dr. Curt D. Furberg, public health sciences professor at Wake Forest University and former chairman of the steering committee of the Allhat study.

    The Evidence Gap

    Comparing Remedies

    Articles in this series will explore medical treatments used despite scant proof they work and will consider steps toward medicine based on evidence.

    Lee Celano for The New York Times

    "There was a feeling there was a political and economic agenda as much as a scientific agenda," said Dr. Michael Weber, professor of medicine at the Health Science Center at Brooklyn and a former investigator in the Allhat study.

    The findings,

    The findings, from one of the biggest clinical trials ever organized by the federal government, promised to save the nation billions of dollars in treating the tens of millions of Americans with hypertension — even if the conclusions did seem to threaten pharmaceutical giants like Pfizer that were making big money on blockbuster hypertension drugs.

    Six years later, though, the use of the inexpensive pills, called diuretics, is far smaller than some of the trial’s organizers had hoped.

    “It should have more than doubled,” said Dr. Curt D. Furberg, a public health sciences professor at Wake Forest University who was the first chairman of the steering committee for the study, which was known by the acronym Allhat.

    “The impact was disappointing.”

    The percentage of hypertension patients receiving a diuretic rose to around 40 percent in the year after the Allhat results were announced, up from 30 to 35 percent beforehand, according to some studies. But use of diuretics has since stayed at that plateau. And over all, use of newer hypertension drugs has grown faster than the use of diuretics since 2002, according to Medco Health Solutions, a pharmacy benefits manager.

    The Allhat experience is worth remembering now, as some policy experts and government officials call for more such studies to directly compare drugs or other treatments, as a way to stem runaway medical costs and improve care.

    The aftereffects of the study show how hard it is to change medical practice, even after a government-sanctioned trial costing $130 million produced what appeared to be solid evidence.

    A confluence of factors blunted Allhat’s impact. One was the simple difficulty of persuading doctors to change their habits. Another was scientific disagreement, as many academic medical experts criticized the trial’s design and the government’s interpretation of the results.