Lilly’s shares rose nearly 7 percent Thursday, to $89.98. Boehringer is privately held.

The Food and Drug Administration approves diabetes drugs if they reduce blood sugar levels. It does not require that the drugs be shown to reduce the risks of the complications of high blood sugar, such as heart attacks, even though that is the real goal of treatment.

“The F.D.A. has given diabetes drugs a bye,” said Dr. David M. Nathan, director of the diabetes center at Massachusetts General Hospital. That is because some studies started decades ago suggested that controlling blood sugar did lower the risk of certain complications, like blindness and kidney disease.

But whether the drugs reduce heart attacks and other cardiovascular problems has been less clear. There was some evidence of benefit in the very long run shown in those early studies. But there have also been counterexamples, including one trial several years ago in which more intensive glucose control raised the risk of death.

In 2007, an analysis by Dr. Nissen suggested that the widely used diabetes drug Avandia increased the risk of heart attacks. While the finding was disputed, the F.D.A. began requiring developers of new diabetes drugs to conduct large trials to rule out the possibility that their drugs increased cardiovascular risk.

Several of those large studies have now been conducted, including one for Merck’s Januvia, and the drugs have generally been found not to raise cardiovascular risk. But they did not decrease the risks, either — until this trial with Jardiance.

The study, paid for by Lilly and Boehringer, involved 7,000 people with Type 2 diabetes who already had cardiovascular disease, so they were at very high risk of heart attacks and strokes. They were randomly assigned to get either Jardiance, which is known generically as empagliflozin, or a placebo. The patients were allowed to take other diabetes drugs as well.

After a median follow-up of about three years, about 10.5 percent of those getting Jardiance had suffered a heart attack or a stroke, or had died from cardiovascular causes, compared with 12.1 percent of those getting a placebo. That works out to about a 14 percent relative reduction in risk.