But there has been wonderment at Mr. Mann’s fascination and persistence with inhaled insulin. He has given his name to MannKind and spent much of his fortune — once estimated in the billions but recently put at $900 million by Forbes — sustaining it. He owns about 40 percent of MannKind, which has lost $2.3 billion since its inception.

Image The inhaler for Afrezza, an insulin developed by MannKind. An advisory panel endorsed the diabetes drug on Tuesday. Credit... Damion Edwards for Mannkind

Mr. Mann, in a statement, said he was pleased with the committee’s endorsement. “Diabetes is a major health problem in the United States,” he said, “and we are committed to bring Afrezza to the many patients who might benefit from this novel product.”

Trading in MannKind shares was halted on Tuesday.

Even if it wins approval, Afrezza might not be a commercial success. MannKind has yet to find the larger pharmaceutical company partner it has said it will need to market and sell the product.

The reason for the skepticism stems in part from Pfizer’s experience. To much fanfare, it won approval for an inhaled insulin called Exubera in 2006. But Exubera flopped, and less than two years later, Pfizer said it would stop selling the product and take a charge of $2.8 billion. Two insulin giants, Novo Nordisk and Eli Lilly, subsequently abandoned their own efforts to develop inhaled insulin.

But Mr. Mann soldiered on, saying the Afrezza inhaler was easier to use and less conspicuous than Pfizer’s inhaler, which was about the size of a tennis ball can. MannKind’s inhaler resembles a whistle and fits easily in the palm of a hand.

MannKind also claims its insulin is medically better because it takes effect faster than even rapid-acting injected insulins. That, it says, reduces the risk of hypoglycemia, a potentially life-threatening condition in which blood sugar drops too low.

However, the F.D.A. staff was skeptical, saying the lower incidence of hypoglycemia might be because Afrezza reduces blood sugar less than injected rapid-acting insulin.