Oct. 2, 2012 -- New research suggests that beta-blocker pills don't prevent heart attacks, strokes or cardiac deaths in patients with heart disease, but doctors are torn over whether there's enough in the study to make them want to stop prescribing the drugs. Beta blockers have been a standard heart medication for decades.

The study, published in the Journal of American Medical Association, looked at nearly 45,000 patients with prior heart attacks, coronary artery disease or risk factors for coronary artery disease, and found that those on beta blockers didn't show significantly lower rates of heart attack, stroke or cardiac death than those not on the medication.

"This is a very compelling study that has the potential to shake up the conventional wisdom that exists regarding the role of beta blockers in the management of patients with cardiovascular disease," said Dr. Randal Thomas, a cardiovascular specialist at the Mayo Clinic. "At a minimum, it will lead to new studies that address this issue once again."

Beta blockers work by blocking adrenalin receptors in the brain that become activated when the body is stressed. Beta blockers are used to treat heart disease, high blood pressure, anxiety and other conditions.

Some doctors say they are glad beta blockers are being questioned because their use had been "written in stone" for so many years, but others say using a non-randomized data sample is not as reliable as a randomized drug trial.

While the authors attempted to account for differences between the patient groups that might have had an impact on their health, they did not have access to information on why some patients were prescribed these drugs and some were not, said Dr. Richard Besser, the chief heath and medical editor at ABC News.

Dr. Melvin Rubenfire, who directs cardiovascular medicine at the University of Michigan, said he'd been hoping for a study like this, but it won't change his prescribing habits because he uses beta blockers only in specific cases. Rubenfire also weans patients off the pills 18 months after they have a heart attack if they experience adverse side effects, such as fatigue and erectile dysfunction.

Rubenfire said the existing data wasn't enough to determine which patients would benefit from beta blockers, and what kinds of beta blockers are better than others. Beta blockers include at least six brand names, including Sectral, Tenormin and Zebeta.

Even study coauthor Christopher Cannon, a professor at Harvard Medical School, said he will continue to prescribe beta blockers to his patients, adding "I would not make too much of this" because the study is only observational.

"All it can do is raise up an idea for us researchers to consider for further study," he said.

Cannon said this research shows that it's unclear whether beta blockers add more benefit than the other therapies developed in the decades since beta blockers became a standard of practice for treating patients with heart disease. Since patients are often taking several drugs, it's hard to pinpoint how much one agent helps compared with another.

Dr. Steven Nissen, who chairs the department of cardiovascular medicine at the Cleveland Clinic Foundation, said the medicine might not be ideal for all of the patients it's prescribed to, but a new randomized, controlled trial will be necessary to change guidelines for prescribing beta blockers.

"Abandonment of this type of therapy for post-MI [post-heart attack] patients based upon an observational study is not warranted," he said.

For the time being, the study raises questions, said Dr. Harlan Kumhulz, a professor of medicine, epidemiology and public health at Yale University.

"The question it raises is about how long after having a heart attack should patients remain on beta blockers?" Kumhulz said, noting that beta-blocker patients didn't have better outcomes than the other patients did after the first year. "The study cannot definitively answer that question -- but raises doubts about the need to continue to take them for the rest of a patient's life."

Dr. Lauren Hughes of the ABC News Medical Unit contributed to this report.