MannKind Corp. announced Wednesday that the Food and Drug Administration won’t approve the Valencia biotech’s Afrezza insulin inhaler until the company conducts new human studies. The studies could delay the product by two years.

After the Wednesday markets closed, MannKind said that the FDA outlined in a letter two studies that it wants the company to conduct. It also wants more information about proposed labeling and packaging of the whistle-sized device, which is smaller and differs in other ways from the original inhaler described in the company’s initial 2009 application. The studies are likely to take several months to design, conduct and analyze.

“It’s not worst case scenario, but it’s pretty bad,” Jon Lecroy of Hapoalim Securities told Reuters. “You’re looking at at least a year delay before they can refile, would be my expectation. And that would start a new review cycle, so I would say it’s probably delayed two years.”

The rejection is a blow to Chief Executive Alfred Mann, a medical device entrepreneur who has sunk $1 billion of his own money into the company. “While we are disappointed … we are encouraged that the FDA is asking for clinical studies only to confirm the bridging and handling of the next-generation device in order to compare it to the device used in our extensive clinical program,” Mann said in a statement.

MannKind has had to overcome concerns by both regulators and investors that its experimental drug isn’t much better than a failed insulin inhaler called Exubera that Pfizer dropped in 2007. MannKind maintains its powdered insulin has a different composition after being dispensed by its inhaler and is less likely to irritate patients’ lungs, and also is more effective in controlling spikes in blood sugar after meals.

MannKind shares on Thursday closed down $2.94, or 32 percent, to $6.17 on the Nasdaq.