WEDNESDAY, Nov. 6 (HealthDay News) -- A new clinical trial appears to have dashed hopes that the most popular drug for treating type 2 diabetes might also be able to reduce the risk of heart attack and stroke in nondiabetics.
Previously, diabetes patients who took metformin, a safe and effective blood sugar-lowering pill, experienced a 39 percent lower risk of heart attack over 10 years in a landmark drug trial in the United Kingdom.
Based on those findings, researchers with the University of Glasgow, in Scotland, set out to see whether metformin would provide similar cardiovascular benefits for people who don't have diabetes.
The new results, published online Nov. 7 in The Lancet Diabetes & Endocrinology, are disappointing, the study authors said.
"We didn't find that any markers of heart risk really looked like they improved in any meaningful way," said study leader Dr. David Preiss, a clinical senior lecturer at the BHF Glasgow Cardiovascular Research Center and the University of Glasgow.
The drug did not have any effect on hardening of the arteries in the neck (the "carotid" arteries), or on the amount of carotid plaque in the blood vessels, the researchers reported. There also were no significant changes in cholesterol or triglyceride (blood fat) levels, or in blood pressure.
However, the drug did prompt weight loss among study participants, opening the door for its potential use as a safe weight-control medication. People taking the drug lost an average of 7 pounds over the course of the 18-month study and had improved blood sugar levels.
"Some people probably use it for that already," Preiss said of metformin's potential as a weight-loss medication. "If you look at the drugs that have been used for weight loss, without exception they've been disastrous and nearly all have been pulled from the market. This drug gave you the kind of weight loss you can get on those medications, and it reduces your risk of diabetes as well."
Metformin has been gaining a reputation as a potential miracle drug. Other studies have shown that it may reduce risk of dementia and cancer of the prostate and pancreas.
The new drug trial involved 173 people who were randomly assigned to take either metformin or an inactive placebo for 18 months. Participants did not have diabetes but already had heart disease and weight problems, and were taking statins to control their cholesterol levels.
After 18 months, the researchers found no improvement in any of their risk factors for heart attack.
"Right now, physicians would not treat patients who are like this with metformin, so this study supports the fact that metformin has no short-term benefit for people with heart disease," said Dr. Robert Eckel, a professor of medicine at the University of Colorado Anschutz Medical Campus. "There were some metabolic benefits, but this study in no way indicates the need to treat patients with heart disease with metformin."
Metformin apparently causes weight loss through appetite suppression, but that weight loss cannot fully account for the improvement in heart attack risk that people with type 2 diabetes enjoy when they take the pill, said Eckel, a past president of the American Heart Association.
"The metformin benefit is in part related to better diabetes control, in part related to weight control and in part due to factors that haven't been identified yet," he said.
The case isn't completely closed on metformin, however. A large trial involving 12,000 patients currently is testing the drug's ability to control blood sugar levels in nondiabetics, but researchers also will look at the data to see if heart attack risk drops.
"We have to be cautious because big trials have surprised us before and will surprise us again," said study author Preiss. "I wouldn't rule it out of having some benefit, but if something fails to improve cholesterol or blood pressure, I for one would be cautious about giving it a big sell-up."
For more about metformin, visit the University of California, San Francisco.
SOURCES: David Preiss, M.R.C.P., clinical senior lecturer, BHF Glasgow Cardiovascular Research Center and the University of Glasgow, Scotland; Robert Eckel, M.D., professor of medicine, Anschutz Medical Campus, University of Colorado, and past president, American Heart Association; Nov. 7, 2013, The Lancet Diabetes & Endocrinology, online