When Dr. C. Michael Gibson, a cardiologist at Harvard Medical School, goes to heart disease meetings, he can’t help noticing a change.

“We will sit around at dinner and halfway through the meal, we will simultaneously push our plates away,” Dr. Gibson said. “We look at each other and laugh and say, ‘You, too?’”

They share what is becoming an open secret: They tried for years to control their weight but are now taking the new obesity drugs manufactured by Eli Lilly and Novo Nordisk.

Dr. Robert Califf, the former chief of the Food and Drug Administration, says he hardly recognizes his colleagues. So many are now so thin.

“Looking good,” he says he tells his fellow cardiologists at conferences and meetings.

There are no studies documenting the percentage of doctors taking the drugs. But physicians “are a good litmus test for drugs that are highly effective,” Dr. Califf said. If doctors who read the papers describing clinical-trial results are rushing to get a new drug, that is an indication that it’s really promising.

His colleagues’ use of Wegovy and Zepbound reminds him of the use of statins, drugs that lower cholesterol, in their early days. Cardiologists, who were most familiar with the consequences of high cholesterol levels, were among the first to take the drugs in large numbers.